[flang-commits] [flang] Revert "[flang][OpenMP] Implement collapse for imperfectly nested loops" (PR #208456)

Caroline Newcombe via flang-commits flang-commits at lists.llvm.org
Thu Jul 9 06:06:23 PDT 2026


https://github.com/cenewcombe created https://github.com/llvm/llvm-project/pull/208456

Reverts llvm/llvm-project#202435

>From 8673792264d4aa28623a4a1e0434820e64593d36 Mon Sep 17 00:00:00 2001
From: Caroline Newcombe <caroline.newcombe at hpe.com>
Date: Thu, 9 Jul 2026 09:06:03 -0400
Subject: [PATCH] =?UTF-8?q?Revert=20"[flang][OpenMP]=20Implement=20collaps?=
 =?UTF-8?q?e=20for=20imperfectly=20nested=20loops=20(#202=E2=80=A6"?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This reverts commit 290f3bc2d12e5875a0be386fad8f6a5dfce9d6a3.
---
 flang/include/flang/Semantics/openmp-utils.h  |   6 -
 flang/lib/Lower/OpenMP/OpenMP.cpp             | 187 +----
 flang/lib/Lower/OpenMP/Utils.cpp              |  33 +-
 flang/lib/Semantics/check-omp-loop.cpp        |  10 -
 flang/lib/Semantics/openmp-utils.cpp          |  87 +--
 .../Lower/OpenMP/collapse-imperfect-nest.f90  | 648 ------------------
 .../Lower/OpenMP/collapse-loop-transform.f90  |  21 -
 flang/test/Semantics/OpenMP/do-collapse.f90   |   8 +-
 .../OpenMP/do-concurrent-collapse-60.f90      |   4 +-
 .../OpenMP/do-concurrent-collapse.f90         |   4 +-
 flang/test/Semantics/OpenMP/do08.f90          |  15 +
 flang/test/Semantics/OpenMP/do10.f90          |   2 +-
 flang/test/Semantics/OpenMP/do13.f90          |  10 +-
 flang/test/Semantics/OpenMP/do15.f90          |   9 +
 flang/test/Semantics/OpenMP/do16.f90          |   6 +
 flang/test/Semantics/OpenMP/do22.f90          | 127 +---
 .../OpenMP/doacross-nesting-omp60.f90         | 148 ----
 .../OpenMP/ordered-nesting-omp50.f90          |  50 --
 .../OpenMP/ordered-nesting-omp51.f90          |  36 -
 19 files changed, 62 insertions(+), 1349 deletions(-)
 delete mode 100644 flang/test/Lower/OpenMP/collapse-imperfect-nest.f90
 delete mode 100644 flang/test/Lower/OpenMP/collapse-loop-transform.f90
 delete mode 100644 flang/test/Semantics/OpenMP/doacross-nesting-omp60.f90
 delete mode 100644 flang/test/Semantics/OpenMP/ordered-nesting-omp50.f90
 delete mode 100644 flang/test/Semantics/OpenMP/ordered-nesting-omp51.f90

diff --git a/flang/include/flang/Semantics/openmp-utils.h b/flang/include/flang/Semantics/openmp-utils.h
index 0764d6e2b05af..6fc65c5e71765 100644
--- a/flang/include/flang/Semantics/openmp-utils.h
+++ b/flang/include/flang/Semantics/openmp-utils.h
@@ -360,12 +360,6 @@ std::optional<std::vector<const parser::DoConstruct *>> CollectAffectedDoLoops(
     const parser::OpenMPLoopConstruct &x, unsigned version,
     SemanticsContext *semaCtx = nullptr);
 
-/// Returns whether the loop nest associated with `x` is a doacross loop nest,
-/// i.e. its body contains an `ordered` directive carrying a doacross
-/// dependence (the `doacross` clause, or the pre-5.2 `depend(sink/source)`
-/// equivalent) that binds to `x`. Such a nest must be perfectly nested.
-bool IsDoacrossAffected(const parser::OpenMPLoopConstruct &x);
-
 struct LoopSequence {
   LoopSequence(const parser::ExecutionPartConstruct &root, unsigned version,
       bool allowAllLoops = false, SemanticsContext *semaCtx = nullptr);
diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index 7939e0db655e4..9c6352b73a585 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -36,7 +36,6 @@
 #include "flang/Optimizer/Builder/BoxValue.h"
 #include "flang/Optimizer/Builder/FIRBuilder.h"
 #include "flang/Optimizer/Builder/Todo.h"
-#include "flang/Optimizer/Dialect/FIROpsSupport.h"
 #include "flang/Optimizer/Dialect/FIRType.h"
 #include "flang/Optimizer/HLFIR/HLFIROps.h"
 #include "flang/Parser/openmp-utils.h"
@@ -933,167 +932,6 @@ static void genNestedEvaluations(lower::AbstractConverter &converter,
     converter.genEval(e);
 }
 
-static mlir::Operation *setLoopVar(lower::AbstractConverter &converter,
-                                   mlir::Location loc, mlir::Value indexVal,
-                                   const semantics::Symbol *sym);
-
-/// Emit the body of a collapsed loop nest, including any intervening code
-/// from imperfect nesting at intermediate levels (CLN relaxation, applied
-/// retroactively for all OMP versions).
-///
-/// Because omp.loop_nest places its entire body at the innermost nesting
-/// level, intervening code must be guarded so that it only executes on the
-/// iterations where the corresponding inner induction variables are at their
-/// initial (for intervening code before nested loop) or final (for intervening
-/// code after nested loop) values.
-///
-/// \param [in] converter - PFT to MLIR conversion interface.
-/// \param [in] outerEval - the evaluation containing the outermost loop
-///                         (typically the OpenMP construct evaluation).
-/// \param [in] collapseValue - number of loops being collapsed (>= 1).
-static void genCollapsedLoopNestBody(lower::AbstractConverter &converter,
-                                     lower::pft::Evaluation &outerEval,
-                                     int collapseValue) {
-  assert(collapseValue >= 1);
-  if (collapseValue == 1) {
-    genNestedEvaluations(converter, outerEval, /*collapseValue=*/1);
-    return;
-  }
-
-  fir::FirOpBuilder &firOpBuilder = converter.getFirOpBuilder();
-  const mlir::Location loc = converter.getCurrentLocation();
-
-  // Get the enclosing omp.loop_nest to access induction variables and bounds.
-  auto loopNestOp = mlir::dyn_cast<mlir::omp::LoopNestOp>(
-      firOpBuilder.getInsertionBlock()->getParentOp());
-  assert(loopNestOp && "expected to be inside omp.loop_nest");
-
-  // Collect before/after evaluations at each intermediate level.
-  struct LevelInfo {
-    llvm::SmallVector<lower::pft::Evaluation *> before;
-    llvm::SmallVector<lower::pft::Evaluation *> after;
-  };
-  llvm::SmallVector<LevelInfo> levels;
-
-  // DO-variable symbol of each collapsed level (index 0 = outermost). Used to
-  // restore an inner loop's variable to its Fortran terminal value before
-  // emitting "after" intervening code (see below).
-  llvm::SmallVector<const semantics::Symbol *> ivSyms;
-
-  lower::pft::Evaluation *curEval = &outerEval;
-  for (int i = 0; i < collapseValue - 1; ++i) {
-    lower::pft::Evaluation *doEval = getNestedDoConstruct(*curEval);
-    const semantics::Symbol *ivSym = getIterationVariableSymbol(*doEval);
-    assert(ivSym && "expected iteration variable on collapsed DO loop");
-    ivSyms.push_back(ivSym);
-    LevelInfo level;
-    bool pastDo = false;
-    for (lower::pft::Evaluation &e : doEval->getNestedEvaluations()) {
-      if (e.getIf<parser::NonLabelDoStmt>() || e.getIf<parser::EndDoStmt>())
-        continue;
-      // Semantics guarantees the only DoConstruct here is the next associated
-      // loop (non-associated DO loops are rejected as intervening code).
-      if (e.getIf<parser::DoConstruct>()) {
-        pastDo = true;
-        continue;
-      }
-      if (!pastDo)
-        level.before.push_back(&e);
-      else
-        level.after.push_back(&e);
-    }
-    levels.push_back(std::move(level));
-    curEval = doEval;
-  }
-  // DO-variable symbol of the innermost collapsed loop must be restored
-  // inside enclosing "after" regions.
-  const semantics::Symbol *innermostIvSym =
-      getIterationVariableSymbol(*getNestedDoConstruct(*curEval));
-  assert(innermostIvSym && "expected iteration variable on collapsed DO loop");
-  ivSyms.push_back(innermostIvSym);
-
-  // Build a guard condition: all induction variables from
-  // startLevel..endLevel-1 equal their respective bound values.
-  // For "before" guards (useLowerBound=true), compare iv == lb (first iter).
-  // For "after" guards (useLowerBound=false), compare iv == last_iv.
-  const auto lbs = loopNestOp.getLoopLowerBounds();
-  const auto ubs = loopNestOp.getLoopUpperBounds();
-  const auto steps = loopNestOp.getLoopSteps();
-
-  // Last value the induction variable at \p lvl actually takes:
-  // lb + ((ub - lb) / step) * step. For unit steps this is exactly ub.
-  auto computeLastIV = [&](const int lvl) -> mlir::Value {
-    const auto constStep = fir::getIntIfConstant(steps[lvl]);
-    if (constStep && (*constStep == 1 || *constStep == -1))
-      return ubs[lvl];
-    const mlir::Value lb = lbs[lvl];
-    const mlir::Value ub = ubs[lvl];
-    const mlir::Value step = steps[lvl];
-    const mlir::Value range =
-        mlir::arith::SubIOp::create(firOpBuilder, loc, ub, lb);
-    const mlir::Value tripMinus1 =
-        mlir::arith::DivSIOp::create(firOpBuilder, loc, range, step);
-    const mlir::Value lastOffset =
-        mlir::arith::MulIOp::create(firOpBuilder, loc, tripMinus1, step);
-    return mlir::arith::AddIOp::create(firOpBuilder, loc, lb, lastOffset);
-  };
-
-  auto buildGuard = [&](const int startLevel, const int endLevel,
-                        const bool useLowerBound) -> mlir::Value {
-    mlir::Value cond;
-    for (int lvl = startLevel; lvl < endLevel; ++lvl) {
-      const mlir::Value iv = loopNestOp.getRegion().getArgument(lvl);
-      const mlir::Value target = useLowerBound ? lbs[lvl] : computeLastIV(lvl);
-      const mlir::Value cmp = mlir::arith::CmpIOp::create(
-          firOpBuilder, loc, mlir::arith::CmpIPredicate::eq, iv, target);
-      if (!cond)
-        cond = cmp;
-      else
-        cond = mlir::arith::AndIOp::create(firOpBuilder, loc, cond, cmp);
-    }
-    return cond;
-  };
-
-  // Emit "before" code at each level, guarded by inner IVs == lower bounds.
-  for (int i = 0; i < static_cast<int>(levels.size()); ++i) {
-    if (levels[i].before.empty())
-      continue;
-    const mlir::Value guard =
-        buildGuard(i + 1, collapseValue, /*useLowerBound=*/true);
-    auto ifOp = fir::IfOp::create(firOpBuilder, loc, guard, /*else*/ false);
-    firOpBuilder.setInsertionPointToStart(&ifOp.getThenRegion().front());
-    for (auto *e : levels[i].before)
-      converter.genEval(*e);
-    firOpBuilder.setInsertionPointAfter(ifOp);
-  }
-
-  // Emit innermost loop body.
-  genNestedEvaluations(converter, *curEval, /*collapseValue=*/1);
-
-  // Emit "after" code at each level (innermost first), guarded by
-  // inner IVs == last iteration values (accounts for non-unit steps).
-  for (int i = static_cast<int>(levels.size()) - 1; i >= 0; --i) {
-    if (levels[i].after.empty())
-      continue;
-    const mlir::Value guard =
-        buildGuard(i + 1, collapseValue, /*useLowerBound=*/false);
-    auto ifOp = fir::IfOp::create(firOpBuilder, loc, guard, /*else*/ false);
-    firOpBuilder.setInsertionPointToStart(&ifOp.getThenRegion().front());
-    // A normally-terminated Fortran DO loop leaves its variable one step past
-    // the last executed value, but the flattened nest leaves each at its last
-    // executed value. Restore the terminal value before running "after" code
-    // that may read it.
-    for (int lvl = i + 1; lvl < collapseValue; ++lvl) {
-      const mlir::Value terminal = mlir::arith::AddIOp::create(
-          firOpBuilder, loc, computeLastIV(lvl), steps[lvl]);
-      setLoopVar(converter, loc, terminal, ivSyms[lvl]);
-    }
-    for (auto *e : levels[i].after)
-      converter.genEval(*e);
-    firOpBuilder.setInsertionPointAfter(ifOp);
-  }
-}
-
 static fir::GlobalOp globalInitialization(lower::AbstractConverter &converter,
                                           fir::FirOpBuilder &firOpBuilder,
                                           const semantics::Symbol &sym,
@@ -1785,13 +1623,6 @@ struct OpWithBodyGenInfo {
     return *this;
   }
 
-  OpWithBodyGenInfo &setCollapseInfo(int value,
-                                     lower::pft::Evaluation &outerEval) {
-    collapseValue = value;
-    outerCollapseEval = &outerEval;
-    return *this;
-  }
-
   /// [inout] converter to use for the clauses.
   lower::AbstractConverter &converter;
   /// [in] Symbol table
@@ -1820,10 +1651,6 @@ struct OpWithBodyGenInfo {
   bool genSkeletonOnly = false;
   /// [in] enables handling of privatized variable unless set to `false`.
   bool privatize = true;
-  /// [in] if set, outermost evaluation and collapse depth for emitting
-  /// intervening code from imperfect collapsed loop nests.
-  lower::pft::Evaluation *outerCollapseEval = nullptr;
-  int collapseValue = 0;
 };
 
 static mlir::Value getReductionOverrideValue(fir::FirOpBuilder &builder,
@@ -2123,11 +1950,7 @@ static void createBodyOfOp(mlir::Operation &op, const OpWithBodyGenInfo &info,
       firOpBuilder.setInsertionPointToEnd(&op.getRegion(0).back());
       auto *temp = lower::genOpenMPTerminator(firOpBuilder, &op, info.loc);
       firOpBuilder.setInsertionPointAfter(marker);
-      if (info.outerCollapseEval)
-        genCollapsedLoopNestBody(info.converter, *info.outerCollapseEval,
-                                 info.collapseValue);
-      else
-        genNestedEvaluations(info.converter, info.eval);
+      genNestedEvaluations(info.converter, info.eval);
       temp->erase();
     }
 
@@ -2983,8 +2806,7 @@ genLoopNestOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
                         directive)
           .setClauses(&item->clauses)
           .setDataSharingProcessor(&dsp)
-          .setGenRegionEntryCb(ivCallback)
-          .setCollapseInfo(nestValue, eval),
+          .setGenRegionEntryCb(ivCallback),
       queue, item, clauseOps);
   converter.overrideExprValues(oldOverrides);
   return loopNestOp;
@@ -3076,7 +2898,7 @@ static void genCanonicalLoopNest(
   // Step 1: Loop prologues
   // Computing the trip count must happen before entering the outermost loop
   lower::pft::Evaluation *innermostEval = nestedEval;
-  for (std::size_t i = 0; i < ivs.size(); ++i) {
+  for ([[maybe_unused]] auto iv : ivs) {
     if (innermostEval->getIf<parser::DoConstruct>()->IsDoConcurrent()) {
       // OpenMP specifies DO CONCURRENT only with the `!omp loop` construct.
       // Will need to add special cases for this combination.
@@ -3158,8 +2980,7 @@ static void genCanonicalLoopNest(
     mlir::Value cli = newcli.getResult();
     clis.push_back(cli);
 
-    if (i + 1 < ivs.size())
-      innermostEval = getNestedDoConstruct(*innermostEval);
+    innermostEval = &*std::next(innermostEval->getNestedEvaluations().begin());
   }
 
   // Step 2: Create nested canoncial loops
diff --git a/flang/lib/Lower/OpenMP/Utils.cpp b/flang/lib/Lower/OpenMP/Utils.cpp
index fd6e8ee16c3e2..2ecc168f207dc 100644
--- a/flang/lib/Lower/OpenMP/Utils.cpp
+++ b/flang/lib/Lower/OpenMP/Utils.cpp
@@ -698,12 +698,7 @@ static void processTileSizesFromOpenMPConstruct(
   }
 }
 
-// Searches the nested evaluations of \p eval for the next DO construct of a
-// loop nest, returning nullptr when there is none left to descend into. This
-// can happen when COLLAPSE counts loops that a transforming construct such as
-// TILE generates from the source DO loops. getNestedDoConstruct wraps this for
-// callers that require a DO construct and asserts when none is found.
-static pft::Evaluation *tryGetNestedDoConstruct(pft::Evaluation &eval) {
+pft::Evaluation *getNestedDoConstruct(pft::Evaluation &eval) {
   for (pft::Evaluation &nested : eval.getNestedEvaluations()) {
     // In an OpenMPConstruct there can be compiler directives:
     // 1 <<OpenMPConstruct>>
@@ -723,18 +718,10 @@ static pft::Evaluation *tryGetNestedDoConstruct(pft::Evaluation &eval) {
     // Loop transformations can introduce nested OpenMP
     // constructs between the directive and the actual do-loop nest.
     if (nested.getIf<parser::OpenMPConstruct>())
-      return tryGetNestedDoConstruct(nested);
-    // Skip valid intervening code in imperfect loop nests
-    continue;
+      return getNestedDoConstruct(nested);
+    assert(false && "Unexpected construct in the nested evaluations");
   }
-  return nullptr;
-}
-
-pft::Evaluation *getNestedDoConstruct(pft::Evaluation &eval) {
-  pft::Evaluation *doConstruct{tryGetNestedDoConstruct(eval)};
-  if (!doConstruct)
-    llvm_unreachable("Expected do loop to be in the nested evaluations");
-  return doConstruct;
+  llvm_unreachable("Expected do loop to be in the nested evaluations");
 }
 
 /// Populates the sizes vector with values if the given OpenMPConstruct
@@ -859,16 +846,8 @@ void collectLoopRelatedInfo(
     iv.push_back(bounds->Name().thing.symbol);
     loopVarTypeSize = std::max(
         loopVarTypeSize, bounds->Name().thing.symbol->GetUltimate().size());
-    if (--collapseValue) {
-      doConstructEval = tryGetNestedDoConstruct(*doConstructEval);
-      // No DO construct left to descend into: COLLAPSE (or a tile SIZES list)
-      // counts loops generated by a nested loop-transforming construct. Not
-      // yet supported in lowering.
-      if (!doConstructEval)
-        TODO(currentLocation,
-             "Collapsing a loop nest that contains a loop-transforming "
-             "construct");
-    }
+    if (--collapseValue)
+      doConstructEval = getNestedDoConstruct(*doConstructEval);
   } while (collapseValue > 0);
 
   convertLoopBounds(converter, currentLocation, result, loopVarTypeSize);
diff --git a/flang/lib/Semantics/check-omp-loop.cpp b/flang/lib/Semantics/check-omp-loop.cpp
index 7023b44253ea9..38b77157e33b8 100644
--- a/flang/lib/Semantics/check-omp-loop.cpp
+++ b/flang/lib/Semantics/check-omp-loop.cpp
@@ -326,16 +326,6 @@ void OmpStructureChecker::CheckNestedConstruct(
     // Check requirements on nest depth.
     auto [needDepth, needPerfect]{
         GetAffectedNestDepthWithReason(beginSpec, version)};
-
-    // Perfect nesting for doacross loop nests is handled differently across
-    // versions. Only in 6.0+ is the requirement keyed off the body
-    // actually containing an ORDERED directive with a doacross dependence
-    // rather than the ORDERED clause, so the body scan applies only to those
-    // later versions.
-    if (!needPerfect && version > 52 && IsDoacrossAffected(x)) {
-      needPerfect = true;
-    }
-
     auto &[haveSema, havePerf]{sequence.depth()};
 
     auto haveDepth{needPerfect ? havePerf : haveSema};
diff --git a/flang/lib/Semantics/openmp-utils.cpp b/flang/lib/Semantics/openmp-utils.cpp
index 96f774fe34a7b..3503eb0e3a004 100644
--- a/flang/lib/Semantics/openmp-utils.cpp
+++ b/flang/lib/Semantics/openmp-utils.cpp
@@ -1296,33 +1296,11 @@ std::pair<WithReason<int64_t>, bool> GetAffectedNestDepthWithReason(
       ocount = std::nullopt;
       oreason = Reason();
     }
-    bool hasOrdered{parser::omp::FindClause(
-                        spec, llvm::omp::Clause::OMPC_ordered) != nullptr};
-    // Perfect-nesting requirement for the ORDERED clause, by version:
-    //
-    //   5.0:     Any ORDERED clause makes the associated loops a doacross loop
-    //            nest that must be perfectly nested, whether or not the clause
-    //            has an argument.
-    //   5.1/5.2: Only an ORDERED clause *with* an argument requires perfect
-    //            nesting; a bare ORDERED clause does not.
-    //   6.0:     Perfect nesting is required only when the body actually
-    //            contains an ORDERED directive with a doacross dependence;
-    //            that is detected separately by the caller via
-    //            IsDoacrossAffected, so ORDERED(n) alone does not force
-    //            perfect nesting here.
     if (ccount < ocount) {
-      return {{ocount.value_or(1), std::move(oreason)}, version <= 52};
+      // `ocount` cannot be std::nullopt here (C++ std guarantee).
+      return {{ocount.value_or(1), std::move(oreason)}, true};
     }
-    // Same rule as above when COLLAPSE drives the depth: ORDERED(n) requires a
-    // perfect nest through 5.2, while > 5.2 defers to IsDoacrossAffected. In
-    // 5.0, an ORDERED clause without argument also requires perfect nesting.
-    // The CLN relaxation for COLLAPSE is applied retroactively for all
-    // versions.
-    bool needPerfect{false};
-    if (version <= 52) {
-      needPerfect = ocount.has_value() || (version == 50 && hasOrdered);
-    }
-    return {{ccount.value_or(1), std::move(creason)}, needPerfect};
+    return {{ccount.value_or(1), std::move(creason)}, true};
   }
 
   if (IsLoopTransforming(dir)) {
@@ -1540,65 +1518,6 @@ std::optional<int64_t> GetMinimumSequenceCount(
   return GetMinimumSequenceCount(std::nullopt, std::nullopt);
 }
 
-namespace {
-/// Visitor that detects an `ordered` directive carrying a doacross dependence
-/// (the `doacross` clause, or the pre-5.2 `depend(sink/source)` equivalent)
-/// that binds to the loop construct being checked. Prunes nested constructs
-/// that start their own associated loop nest, but descends into
-/// loop-transforming constructs (e.g. tile, unroll), whose generated loops
-/// extend the current nest.
-struct DoacrossFinder {
-  bool found{false};
-  bool inOrdered{false};
-  template <typename T> bool Pre(const T &) { return !found; }
-  template <typename T> void Post(const T &) {}
-
-  // Prune nested constructs that start their own associated loop nest; a
-  // doacross inside them binds there, not here. Loop-transforming constructs
-  // are the exception: their generated loops extend the current nest, so a
-  // doacross inside one still binds to the construct being checked.
-  bool Pre(const parser::OmpBlockConstruct &) { return false; }
-  bool Pre(const parser::OpenMPLoopConstruct &x) {
-    if (IsLoopTransforming(x.BeginDir().DirId())) {
-      return !found;
-    }
-    return false;
-  }
-
-  bool Pre(const parser::OpenMPSimpleStandaloneConstruct &x) {
-    inOrdered = x.v.DirId() == llvm::omp::Directive::OMPD_ordered;
-    return !found;
-  }
-  void Post(const parser::OpenMPSimpleStandaloneConstruct &) {
-    inOrdered = false;
-  }
-
-  bool Pre(const parser::OmpDoacross &) {
-    if (inOrdered) {
-      found = true;
-    }
-    return false;
-  }
-};
-
-static bool ContainsOrderedDoacross(const parser::Block &block) {
-  DoacrossFinder finder;
-  parser::Walk(block, finder);
-  return finder.found;
-}
-} // namespace
-
-bool IsDoacrossAffected(const parser::OpenMPLoopConstruct &x) {
-  // A loop nest is doacross-affected when it has an `ordered` clause and a
-  // stand-alone `ordered` construct carrying a doacross dependence is closely
-  // nested in its body.
-  const parser::OmpDirectiveSpecification &spec{x.BeginDir()};
-  if (!parser::omp::FindClause(spec, llvm::omp::Clause::OMPC_ordered)) {
-    return false;
-  }
-  return ContainsOrderedDoacross(std::get<parser::Block>(x.t));
-}
-
 /// Collect the DO loops that are affected directly by the given loop
 /// transformation. Not all DO loops nested in the associated nest are
 /// affected by the top-level loop transformation, e.g.
diff --git a/flang/test/Lower/OpenMP/collapse-imperfect-nest.f90 b/flang/test/Lower/OpenMP/collapse-imperfect-nest.f90
deleted file mode 100644
index e963049090f49..0000000000000
--- a/flang/test/Lower/OpenMP/collapse-imperfect-nest.f90
+++ /dev/null
@@ -1,648 +0,0 @@
-! Test lowering of imperfectly nested collapse loops (CLN relaxation).
-! Intervening code is guarded by IV comparisons to restore correct
-! execution frequency and ordering within the flat omp.loop_nest body.
-
-! RUN: %flang_fc1 -fopenmp -emit-hlfir %s -o - | FileCheck %s
-
-! CHECK-LABEL: func.func @_QPcollapse2_imperfect
-subroutine collapse2_imperfect(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    x = x + 1
-    do j = 1, n
-      x = x + j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{.*}}, %[[LB_J:.*]]) to
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! Guard: j == lower_bound (before code executes once per i)
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[LB_J]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! Intervening code: x = x + 1
-! CHECK:             %[[X1:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:             %[[C1:.*]] = arith.constant 1 : i32
-! CHECK:             %[[ADD1:.*]] = arith.addi %[[X1]], %[[C1]] : i32
-! CHECK:             hlfir.assign %[[ADD1]] to %{{.*}} : i32, !fir.ref<i32>
-! CHECK:           }
-! Innermost body: x = x + j
-! CHECK:           %[[X2:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:           %[[JVAL:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:           %[[ADD2:.*]] = arith.addi %[[X2]], %[[JVAL]] : i32
-! CHECK:           hlfir.assign %[[ADD2]] to %{{.*}} : i32, !fir.ref<i32>
-! CHECK:           omp.yield
-
-! CHECK-LABEL: func.func @_QPcollapse3_imperfect
-subroutine collapse3_imperfect(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j, k
-
-  !$omp do collapse(3)
-  do i = 1, n
-    x = x + i
-    do j = 1, n
-      x = x + j
-      do k = 1, n
-        x = x + k
-      end do
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I3:.*]], %[[J3:.*]], %[[K3:.*]]) : i32 =
-! CHECK-SAME:      (%{{.*}}, %[[LB_J3:.*]], %[[LB_K3:.*]]) to
-! CHECK:           hlfir.assign %[[I3]]
-! CHECK:           hlfir.assign %[[J3]]
-! CHECK:           hlfir.assign %[[K3]]
-! Guard: j == lb_j AND k == lb_k (level 0 before code, once per i)
-! CHECK:           %[[CMP_J:.*]] = arith.cmpi eq, %[[J3]], %[[LB_J3]] : i32
-! CHECK:           %[[CMP_K1:.*]] = arith.cmpi eq, %[[K3]], %[[LB_K3]] : i32
-! CHECK:           %[[AND1:.*]] = arith.andi %[[CMP_J]], %[[CMP_K1]] : i1
-! CHECK:           fir.if %[[AND1]] {
-! Intervening code at level 0: x = x + i
-! CHECK:             %[[XI:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:             %[[IVAL:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:             %[[ADDI:.*]] = arith.addi %[[XI]], %[[IVAL]] : i32
-! CHECK:             hlfir.assign %[[ADDI]] to %{{.*}} : i32, !fir.ref<i32>
-! CHECK:           }
-! Guard: k == lb_k (level 1 before code, once per (i,j))
-! CHECK:           %[[CMP_K2:.*]] = arith.cmpi eq, %[[K3]], %[[LB_K3]] : i32
-! CHECK:           fir.if %[[CMP_K2]] {
-! Intervening code at level 1: x = x + j
-! CHECK:             %[[XJ:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:             %[[JVAL3:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:             %[[ADDJ:.*]] = arith.addi %[[XJ]], %[[JVAL3]] : i32
-! CHECK:             hlfir.assign %[[ADDJ]] to %{{.*}} : i32, !fir.ref<i32>
-! CHECK:           }
-! Innermost body: x = x + k
-! CHECK:           %[[XK:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:           %[[KVAL:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:           %[[ADDK:.*]] = arith.addi %[[XK]], %[[KVAL]] : i32
-! CHECK:           hlfir.assign %[[ADDK]] to %{{.*}} : i32, !fir.ref<i32>
-! CHECK:           omp.yield
-
-! CHECK-LABEL: func.func @_QPcollapse2_both_sides
-subroutine collapse2_both_sides(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp simd collapse(2)
-  do i = 1, n
-    x = x + 1
-    do j = 1, n
-      x = x + j
-    end do
-    call ext_sub(x)
-  end do
-  !$omp end simd
-end subroutine
-
-! CHECK:       omp.simd
-! CHECK-NEXT:    omp.loop_nest (%[[I4:.*]], %[[J4:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J4:[^)]*]]) to (%{{[^)]*}}, %[[UB_J4:[^)]*]])
-! CHECK:           hlfir.assign %[[I4]]
-! CHECK:           hlfir.assign %[[J4]]
-! Guard: j == lower_bound (before code)
-! CHECK:           %[[CMP_B:.*]] = arith.cmpi eq, %[[J4]], %[[LB_J4]] : i32
-! CHECK:           fir.if %[[CMP_B]] {
-! Intervening code before inner loop: x = x + 1
-! CHECK:             %[[XB:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:             %[[CB:.*]] = arith.constant 1 : i32
-! CHECK:             %[[ADDB:.*]] = arith.addi %[[XB]], %[[CB]] : i32
-! CHECK:             hlfir.assign %[[ADDB]] to %{{.*}} : i32, !fir.ref<i32>
-! CHECK:           }
-! Innermost body: x = x + j
-! CHECK:           %[[XIN:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:           %[[JIN:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:           %[[ADDIN:.*]] = arith.addi %[[XIN]], %[[JIN]] : i32
-! CHECK:           hlfir.assign %[[ADDIN]] to %{{.*}} : i32, !fir.ref<i32>
-! Guard: j == upper_bound (after code)
-! CHECK:           %[[CMP_A:.*]] = arith.cmpi eq, %[[J4]], %[[UB_J4]] : i32
-! CHECK:           fir.if %[[CMP_A]] {
-! Intervening code after inner loop: call ext_sub(x)
-! CHECK:             fir.call @_QPext_sub
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(3) with both before and after code at multiple levels.
-! CHECK-LABEL: func.func @_QPcollapse3_both_sides
-subroutine collapse3_both_sides(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j, k
-
-  !$omp do collapse(3)
-  do i = 1, n
-    x = x + i
-    do j = 1, n
-      x = x + j
-      do k = 1, n
-        x = x + k
-      end do
-      x = x - j
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]], %[[K:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]], %[[LB_K:[^)]*]]) to (%{{[^)]*}}, %[[UB_J:[^)]*]], %[[UB_K:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! CHECK:           hlfir.assign %[[K]]
-!
-! --- "before" guards (outermost level first) ---
-!
-! Guard level 0 before: j == lb_j AND k == lb_k (once per i)
-! CHECK:           %[[CJ1:.*]] = arith.cmpi eq, %[[J]], %[[LB_J]] : i32
-! CHECK:           %[[CK1:.*]] = arith.cmpi eq, %[[K]], %[[LB_K]] : i32
-! CHECK:           %[[AND1:.*]] = arith.andi %[[CJ1]], %[[CK1]] : i1
-! CHECK:           fir.if %[[AND1]] {
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Guard level 1 before: k == lb_k (once per (i,j))
-! CHECK:           %[[CK2:.*]] = arith.cmpi eq, %[[K]], %[[LB_K]] : i32
-! CHECK:           fir.if %[[CK2]] {
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-!
-! --- innermost body: x = x + k ---
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-!
-! --- "after" guards (innermost level first) ---
-!
-! Guard level 1 after: k == ub_k (once per (i,j))
-! CHECK:           %[[CK3:.*]] = arith.cmpi eq, %[[K]], %[[UB_K]] : i32
-! CHECK:           fir.if %[[CK3]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Guard level 0 after: j == ub_j AND k == ub_k (once per i)
-! CHECK:           %[[CJ2:.*]] = arith.cmpi eq, %[[J]], %[[UB_J]] : i32
-! CHECK:           %[[CK4:.*]] = arith.cmpi eq, %[[K]], %[[UB_K]] : i32
-! CHECK:           %[[AND2:.*]] = arith.andi %[[CJ2]], %[[CK4]] : i1
-! CHECK:           fir.if %[[AND2]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(4) with imperfect nesting at some levels and perfectly nested
-! innermost loops. Level 0 (i->j) has before+after, level 1 (j->k) has before
-! only, level 2 (k->l) is perfectly nested. This exercises skipping empty levels.
-! CHECK-LABEL: func.func @_QPcollapse4_mixed
-subroutine collapse4_mixed(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j, k, l
-
-  !$omp do collapse(4)
-  do i = 1, n
-    x = x + i
-    do j = 1, n
-      x = x + j
-      do k = 1, n
-        do l = 1, n
-          x = x + l
-        end do
-      end do
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]], %[[K:.*]], %[[L:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]], %[[LB_K:[^)]*]], %[[LB_L:[^)]*]]) to (%{{[^)]*}}, %[[UB_J:[^)]*]], %[[UB_K:[^)]*]], %[[UB_L:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! CHECK:           hlfir.assign %[[K]]
-! CHECK:           hlfir.assign %[[L]]
-!
-! --- "before" guards ---
-!
-! Guard level 0 before: j == lb_j AND k == lb_k AND l == lb_l (once per i)
-! CHECK:           %[[CJ1:.*]] = arith.cmpi eq, %[[J]], %[[LB_J]] : i32
-! CHECK:           %[[CK1:.*]] = arith.cmpi eq, %[[K]], %[[LB_K]] : i32
-! CHECK:           %[[A1:.*]] = arith.andi %[[CJ1]], %[[CK1]] : i1
-! CHECK:           %[[CL1:.*]] = arith.cmpi eq, %[[L]], %[[LB_L]] : i32
-! CHECK:           %[[A2:.*]] = arith.andi %[[A1]], %[[CL1]] : i1
-! CHECK:           fir.if %[[A2]] {
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Guard level 1 before: k == lb_k AND l == lb_l (once per (i,j))
-! CHECK:           %[[CK2:.*]] = arith.cmpi eq, %[[K]], %[[LB_K]] : i32
-! CHECK:           %[[CL2:.*]] = arith.cmpi eq, %[[L]], %[[LB_L]] : i32
-! CHECK:           %[[A3:.*]] = arith.andi %[[CK2]], %[[CL2]] : i1
-! CHECK:           fir.if %[[A3]] {
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Level 2 (k->l) is perfectly nested: no guard emitted.
-!
-! --- innermost body: x = x + l ---
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-!
-! --- "after" guards (innermost first) ---
-!
-! Level 2 after: empty (perfectly nested), no guard emitted.
-! Level 1 after: empty, no guard emitted.
-! Guard level 0 after: j == ub_j AND k == ub_k AND l == ub_l (once per i)
-! CHECK:           %[[CJ2:.*]] = arith.cmpi eq, %[[J]], %[[UB_J]] : i32
-! CHECK:           %[[CK3:.*]] = arith.cmpi eq, %[[K]], %[[UB_K]] : i32
-! CHECK:           %[[A4:.*]] = arith.andi %[[CJ2]], %[[CK3]] : i1
-! CHECK:           %[[CL3:.*]] = arith.cmpi eq, %[[L]], %[[UB_L]] : i32
-! CHECK:           %[[A5:.*]] = arith.andi %[[A4]], %[[CL3]] : i1
-! CHECK:           fir.if %[[A5]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(2) with only after-code (no before-code). Exercises the path
-! where levels[i].before.empty() is true and the "before" loop is entirely skipped.
-! CHECK-LABEL: func.func @_QPcollapse2_after_only
-subroutine collapse2_after_only(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    do j = 1, n
-      x = x + j
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %{{[^)]*}}) to (%{{[^)]*}}, %[[UB_J:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! No "before" guard emitted (level 0 before is empty).
-! Innermost body: x = x + j
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! Guard: j == upper_bound (after code)
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[UB_J]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(2) with multiple statements inside a single guard. Verifies
-! that all evals in level.before land inside the same fir.if block.
-! CHECK-LABEL: func.func @_QPcollapse2_multi_stmt
-subroutine collapse2_multi_stmt(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    x = x + 1
-    x = x + i
-    do j = 1, n
-      x = x + j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]]) to
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! Guard: j == lower_bound (before code, multiple statements in one guard)
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[LB_J]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! First intervening statement: x = x + 1
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! Second intervening statement: x = x + i
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Innermost body: x = x + j
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! CHECK:           omp.yield
-
-! Test collapse(2) with non-unit lower bound on inner loop. Verifies the guard
-! compares against the actual loop lower bound operand (3, not 1).
-! CHECK-LABEL: func.func @_QPcollapse2_nonunit_lb
-subroutine collapse2_nonunit_lb(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    x = x + i
-    do j = 3, n
-      x = x + j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]]) to
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! Guard: j == lb_j (lb_j is 3, not 1)
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[LB_J]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Innermost body: x = x + j
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! CHECK:           omp.yield
-
-! Test collapse(3) with after-only at level 0 and before-only at level 1.
-! Exercises the independent skip logic at each level in both emission loops.
-! CHECK-LABEL: func.func @_QPcollapse3_mixed_sides
-subroutine collapse3_mixed_sides(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j, k
-
-  !$omp do collapse(3)
-  do i = 1, n
-    do j = 1, n
-      x = x + j
-      do k = 1, n
-        x = x + k
-      end do
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]], %[[K:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %{{[^)]*}}, %[[LB_K:[^)]*]]) to (%{{[^)]*}}, %[[UB_J:[^)]*]], %[[UB_K:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! CHECK:           hlfir.assign %[[K]]
-! Level 0 before: empty (skipped).
-! Guard level 1 before: k == lb_k (once per (i,j))
-! CHECK:           %[[CK:.*]] = arith.cmpi eq, %[[K]], %[[LB_K]] : i32
-! CHECK:           fir.if %[[CK]] {
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Innermost body: x = x + k
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! Level 1 after: empty (skipped).
-! Guard level 0 after: j == ub_j AND k == ub_k (once per i)
-! CHECK:           %[[CJ:.*]] = arith.cmpi eq, %[[J]], %[[UB_J]] : i32
-! CHECK:           %[[CK2:.*]] = arith.cmpi eq, %[[K]], %[[UB_K]] : i32
-! CHECK:           %[[AND:.*]] = arith.andi %[[CJ]], %[[CK2]] : i1
-! CHECK:           fir.if %[[AND]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(2) with non-unit positive step and after-code.
-! The after guard must compare iv against the last executed value
-! (lb + ((ub - lb) / step) * step), not the upper bound directly.
-! For do j = 1, 10, 4: last_iv = 1 + ((10-1)/4)*4 = 1 + 8 = 9.
-! CHECK-LABEL: func.func @_QPcollapse2_nonunit_step_after
-subroutine collapse2_nonunit_step_after(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    do j = 1, 10, 4
-      x = x + j
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]]) to (%{{[^)]*}}, %[[UB_J:[^)]*]]) inclusive step (%{{[^)]*}}, %[[STEP_J:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! Innermost body: x = x + j
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! After guard: compute last_iv = lb + ((ub - lb) / step) * step
-! CHECK:           %[[RANGE:.*]] = arith.subi %[[UB_J]], %[[LB_J]] : i32
-! CHECK:           %[[DIV:.*]] = arith.divsi %[[RANGE]], %[[STEP_J]] : i32
-! CHECK:           %[[MUL:.*]] = arith.muli %[[DIV]], %[[STEP_J]] : i32
-! CHECK:           %[[LAST:.*]] = arith.addi %[[LB_J]], %[[MUL]] : i32
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[LAST]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(2) with negative step and after-code.
-! For do j = 10, 1, -4: last_iv = 10 + ((1-10)/(-4))*(-4) = 10 + (2*-4) = 2.
-! CHECK-LABEL: func.func @_QPcollapse2_negative_step_after
-subroutine collapse2_negative_step_after(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    do j = 10, 1, -4
-      x = x + j
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]]) to (%{{[^)]*}}, %[[UB_J:[^)]*]]) inclusive step (%{{[^)]*}}, %[[STEP_J:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! Innermost body: x = x + j
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! After guard: compute last_iv for negative step
-! CHECK:           %[[RANGE:.*]] = arith.subi %[[UB_J]], %[[LB_J]] : i32
-! CHECK:           %[[DIV:.*]] = arith.divsi %[[RANGE]], %[[STEP_J]] : i32
-! CHECK:           %[[MUL:.*]] = arith.muli %[[DIV]], %[[STEP_J]] : i32
-! CHECK:           %[[LAST:.*]] = arith.addi %[[LB_J]], %[[MUL]] : i32
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[LAST]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(3) with non-unit step on the middle loop (not innermost).
-! For do j = 1, n, 3: last_iv = lb + ((ub - lb) / step) * step (runtime).
-! CHECK-LABEL: func.func @_QPcollapse3_nonunit_step_middle
-subroutine collapse3_nonunit_step_middle(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j, k
-
-  !$omp do collapse(3)
-  do i = 1, n
-    do j = 1, n, 3
-      x = x + j
-      do k = 1, n
-        x = x + k
-      end do
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]], %[[K:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]], %[[LB_K:[^)]*]]) to (%{{[^)]*}}, %[[UB_J:[^)]*]], %[[UB_K:[^)]*]]) inclusive step (%{{[^)]*}}, %[[STEP_J:[^)]*]], %{{[^)]*}})
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! CHECK:           hlfir.assign %[[K]]
-! Guard level 1 before: k == lb_k (once per (i,j))
-! CHECK:           %[[CK1:.*]] = arith.cmpi eq, %[[K]], %[[LB_K]] : i32
-! CHECK:           fir.if %[[CK1]] {
-! CHECK:             arith.addi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! Innermost body: x = x + k
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! Guard level 0 after: must compute last_iv for j (non-unit step) AND k == ub_k
-! CHECK:           %[[RANGE:.*]] = arith.subi %[[UB_J]], %[[LB_J]] : i32
-! CHECK:           %[[DIV:.*]] = arith.divsi %[[RANGE]], %[[STEP_J]] : i32
-! CHECK:           %[[MUL:.*]] = arith.muli %[[DIV]], %[[STEP_J]] : i32
-! CHECK:           %[[LASTJ:.*]] = arith.addi %[[LB_J]], %[[MUL]] : i32
-! CHECK:           %[[CJ:.*]] = arith.cmpi eq, %[[J]], %[[LASTJ]] : i32
-! CHECK:           %[[CK2:.*]] = arith.cmpi eq, %[[K]], %[[UB_K]] : i32
-! CHECK:           %[[AND:.*]] = arith.andi %[[CJ]], %[[CK2]] : i1
-! CHECK:           fir.if %[[AND]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test collapse(2) with a dynamic (runtime) step value.
-! The step is not a compile-time constant, so the last_iv computation
-! cannot be folded away and must remain as arith ops in the IR.
-! CHECK-LABEL: func.func @_QPcollapse2_dynamic_step_after
-subroutine collapse2_dynamic_step_after(n, s, x)
-  integer, intent(in) :: n, s
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    do j = 1, n, s
-      x = x + j
-    end do
-    x = x - i
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %[[LB_J:[^)]*]]) to (%{{[^)]*}}, %[[UB_J:[^)]*]]) inclusive step (%{{[^)]*}}, %[[STEP_J:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! CHECK:           hlfir.assign %[[J]]
-! Innermost body: x = x + j
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! After guard: dynamic step forces last_iv computation to stay in IR
-! CHECK:           %[[RANGE:.*]] = arith.subi %[[UB_J]], %[[LB_J]] : i32
-! CHECK:           %[[DIV:.*]] = arith.divsi %[[RANGE]], %[[STEP_J]] : i32
-! CHECK:           %[[MUL:.*]] = arith.muli %[[DIV]], %[[STEP_J]] : i32
-! CHECK:           %[[LAST:.*]] = arith.addi %[[LB_J]], %[[MUL]] : i32
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[LAST]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! CHECK:             arith.subi
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
-
-! Test that "after" code reading an inner DO variable sees the Fortran
-! terminal value (lb + tripcount*step, i.e. one past the last executed
-! value), not the last executed value the flattened nest leaves it at.
-! The after guard must restore j to ub + step before the after code runs.
-! CHECK-LABEL: func.func @_QPcollapse2_after_reads_inner
-subroutine collapse2_after_reads_inner(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(2)
-  do i = 1, n
-    do j = 1, n
-      x = x + 1
-    end do
-    x = x + j
-  end do
-  !$omp end do
-end subroutine
-
-! CHECK:       omp.wsloop
-! CHECK-NEXT:    omp.loop_nest (%[[I:.*]], %[[J:.*]]) : i32 =
-! CHECK-SAME:      (%{{[^)]*}}, %{{[^)]*}}) to (%{{[^)]*}}, %[[UB_J:[^)]*]]) inclusive step (%{{[^)]*}}, %[[STEP_J:[^)]*]])
-! CHECK:           hlfir.assign %[[I]]
-! Capture j's storage from the loop-variable store so the restore and the
-! after-code read can be tied to the same address.
-! CHECK:           hlfir.assign %[[J]] to %[[J_ADDR:.*]] : i32, !fir.ref<i32>
-! Innermost body: x = x + 1
-! CHECK:           arith.addi
-! CHECK:           hlfir.assign
-! Guard: j == ub_j (unit-step fast path compares against the upper bound)
-! CHECK:           %[[CMP:.*]] = arith.cmpi eq, %[[J]], %[[UB_J]] : i32
-! CHECK:           fir.if %[[CMP]] {
-! Restore j's storage to its Fortran terminal value (ub + step).
-! CHECK:             %[[TERM:.*]] = arith.addi %[[UB_J]], %[[STEP_J]] : i32
-! CHECK:             hlfir.assign %[[TERM]] to %[[J_ADDR]] : i32, !fir.ref<i32>
-! After code reads the restored j: x = x + j.
-! CHECK:             %[[XLD:.*]] = fir.load %{{.*}} : !fir.ref<i32>
-! CHECK:             %[[JLD:.*]] = fir.load %[[J_ADDR]] : !fir.ref<i32>
-! CHECK:             arith.addi %[[XLD]], %[[JLD]] : i32
-! CHECK:             hlfir.assign
-! CHECK:           }
-! CHECK:           omp.yield
diff --git a/flang/test/Lower/OpenMP/collapse-loop-transform.f90 b/flang/test/Lower/OpenMP/collapse-loop-transform.f90
deleted file mode 100644
index c394ed9f53d21..0000000000000
--- a/flang/test/Lower/OpenMP/collapse-loop-transform.f90
+++ /dev/null
@@ -1,21 +0,0 @@
-! COLLAPSE over a nested loop-transforming construct (e.g. TILE) is accepted by
-! semantics but not yet supported in lowering. Check for a "not yet
-! implemented" message instead of a compiler crash.
-
-! RUN: not %flang_fc1 -emit-hlfir -fopenmp -fopenmp-version=60 -o - %s 2>&1 | FileCheck %s
-
-subroutine collapse_tile(n, x)
-  integer, intent(in) :: n
-  integer, intent(inout) :: x
-  integer :: i, j
-
-  !$omp do collapse(4)
-  !$omp tile sizes(2, 2)
-  do i = 1, n
-    do j = 1, n
-      x = x + i + j
-    end do
-  end do
-end subroutine
-
-! CHECK: not yet implemented: Collapsing a loop nest that contains a loop-transforming construct
diff --git a/flang/test/Semantics/OpenMP/do-collapse.f90 b/flang/test/Semantics/OpenMP/do-collapse.f90
index 9148f6558b000..2804ae00ad7be 100644
--- a/flang/test/Semantics/OpenMP/do-collapse.f90
+++ b/flang/test/Semantics/OpenMP/do-collapse.f90
@@ -3,7 +3,7 @@
 ! 2.7.1 Collapse Clause
 program omp_doCollapse
   integer:: i,j
-  !ERROR: This construct requires a nest of depth 3, but the associated nest is a nest of depth 2
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
   !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do collapse(3)
   do i = 1,10
@@ -15,7 +15,7 @@ program omp_doCollapse
 
   do i = 1,10
     do j = 1, 10
-      !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+      !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
       !BECAUSE: COLLAPSE clause was specified with argument 2
       !$omp do collapse(2)
       do k = 1, 10
@@ -25,7 +25,7 @@ program omp_doCollapse
     end do
   end do
 
-  !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp parallel do collapse(2)
     do i = 1, 3
@@ -35,7 +35,7 @@ program omp_doCollapse
       end do
     end do
 
-  !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 2
   !ERROR: At most one COLLAPSE clause can appear on SIMD directive
   !$omp simd collapse(2) collapse(1)
diff --git a/flang/test/Semantics/OpenMP/do-concurrent-collapse-60.f90 b/flang/test/Semantics/OpenMP/do-concurrent-collapse-60.f90
index 75351cdf7190c..4ba8e71a26323 100644
--- a/flang/test/Semantics/OpenMP/do-concurrent-collapse-60.f90
+++ b/flang/test/Semantics/OpenMP/do-concurrent-collapse-60.f90
@@ -3,7 +3,7 @@
 subroutine f
   integer :: i
 
-  !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp parallel do collapse(2)
   do i = 1, 1
@@ -42,7 +42,7 @@ subroutine f
     print *, j
   end do
 
-  !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp loop collapse(2)
   do i = 1, 1
diff --git a/flang/test/Semantics/OpenMP/do-concurrent-collapse.f90 b/flang/test/Semantics/OpenMP/do-concurrent-collapse.f90
index 0a6906b0e2e63..7cd10518d845a 100644
--- a/flang/test/Semantics/OpenMP/do-concurrent-collapse.f90
+++ b/flang/test/Semantics/OpenMP/do-concurrent-collapse.f90
@@ -1,7 +1,7 @@
 !RUN: %python %S/../test_errors.py %s %flang -fopenmp
 
 integer :: i, j
-! ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+! ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
 ! BECAUSE: COLLAPSE clause was specified with argument 2
 !$omp parallel do collapse(2)
 do i = 1, 1
@@ -33,7 +33,7 @@
   print *, j
 end do
 
-! ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+! ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
 ! BECAUSE: COLLAPSE clause was specified with argument 2
 !$omp loop collapse(2)
 do i = 1, 1
diff --git a/flang/test/Semantics/OpenMP/do08.f90 b/flang/test/Semantics/OpenMP/do08.f90
index 24755022f0296..300485f067b1d 100644
--- a/flang/test/Semantics/OpenMP/do08.f90
+++ b/flang/test/Semantics/OpenMP/do08.f90
@@ -7,8 +7,11 @@ program omp
   logical cond(10,10,10)
   cond = .false.
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 1
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
+    !BECAUSE: This code prevents perfect nesting
     !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
     if (i .lt. 1) cycle
     do j = 0, 10
@@ -19,9 +22,12 @@ program omp
   end do
   !$omp end do
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
     do j = 0, 10
+      !BECAUSE: This code prevents perfect nesting
       !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
       if (i .lt. 1) cycle
       do k  = 0, 10
@@ -31,8 +37,11 @@ program omp
   end do
   !$omp end do
 
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
+  !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp do  collapse(2)
   do i = 0, 10
+    !BECAUSE: This code prevents perfect nesting
     !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
     if (i .lt. 1) cycle
     do j = 0, 10
@@ -44,8 +53,11 @@ program omp
   !$omp end do
 
 
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
+  !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp do  collapse(2)
   foo: do i = 0, 10
+    !BECAUSE: This code prevents perfect nesting
     !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
     if (i .lt. 1) cycle foo
     do j = 0, 10
@@ -57,9 +69,12 @@ program omp
   !$omp end do
 
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do collapse(3)
   do 60 i=2,200,2
     do j=1,10
+      !BECAUSE: This code prevents perfect nesting
       !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
       if (i == 100) cycle
       do k = 1, 10
diff --git a/flang/test/Semantics/OpenMP/do10.f90 b/flang/test/Semantics/OpenMP/do10.f90
index 1fae5e098dc56..1878864a4a5db 100644
--- a/flang/test/Semantics/OpenMP/do10.f90
+++ b/flang/test/Semantics/OpenMP/do10.f90
@@ -14,7 +14,7 @@ program omp_do
   end do
   !$omp end do
 
-  !ERROR: This construct requires a nest of depth 3, but the associated nest is a nest of depth 2
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
   !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do collapse(3)
   do i = 1, 10
diff --git a/flang/test/Semantics/OpenMP/do13.f90 b/flang/test/Semantics/OpenMP/do13.f90
index dd9f4be03e7e1..6d5e799e951b0 100644
--- a/flang/test/Semantics/OpenMP/do13.f90
+++ b/flang/test/Semantics/OpenMP/do13.f90
@@ -5,7 +5,7 @@
 program omp
   integer i, j, k
 
-  !ERROR: This construct requires a nest of depth 3, but the associated nest is a nest of depth 1
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
@@ -20,7 +20,7 @@ program omp
   end do
   !$omp end do
 
-  !ERROR: This construct requires a nest of depth 3, but the associated nest is a nest of depth 2
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
   !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
@@ -35,7 +35,7 @@ program omp
   end do
   !$omp end do
 
-  !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp do  collapse(2)
   do i = 0, 10
@@ -51,7 +51,7 @@ program omp
   !$omp end do
 
 
-  !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp do  collapse(2)
   foo: do i = 0, 10
@@ -67,7 +67,7 @@ program omp
   !$omp end do
 
 
-  !ERROR: This construct requires a nest of depth 3, but the associated nest is a nest of depth 2
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
   !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do collapse(3)
   do 60 i=1,10
diff --git a/flang/test/Semantics/OpenMP/do15.f90 b/flang/test/Semantics/OpenMP/do15.f90
index 96c195b2d1306..00baa0c431c5f 100644
--- a/flang/test/Semantics/OpenMP/do15.f90
+++ b/flang/test/Semantics/OpenMP/do15.f90
@@ -5,8 +5,11 @@
 program omp
   integer i, j, k
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 1
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
+    !BECAUSE: This code prevents perfect nesting
     if (i .lt. 1) then
       !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
       cycle
@@ -19,9 +22,12 @@ program omp
   end do
   !$omp end do
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
     do j = 0, 10
+      !BECAUSE: This code prevents perfect nesting
       if (i .lt. 1) then
         !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
         cycle
@@ -50,9 +56,12 @@ program omp
   !$omp end do
 
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   foo: do i = 0, 10
     foo1: do j = 0, 10
+      !BECAUSE: This code prevents perfect nesting
       if (i .lt. 1) then
         !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
         cycle foo
diff --git a/flang/test/Semantics/OpenMP/do16.f90 b/flang/test/Semantics/OpenMP/do16.f90
index 2a871156de75f..35d94b17f3c68 100644
--- a/flang/test/Semantics/OpenMP/do16.f90
+++ b/flang/test/Semantics/OpenMP/do16.f90
@@ -5,8 +5,11 @@
 program omp
   integer i, j, k
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 1
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
+    !BECAUSE: This code prevents perfect nesting
     select case (i)
     case(1)
       !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
@@ -20,9 +23,12 @@ program omp
   end do
   !$omp end do
 
+  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 2
+  !BECAUSE: COLLAPSE clause was specified with argument 3
   !$omp do  collapse(3)
   do i = 0, 10
     do j = 0, 10
+      !BECAUSE: This code prevents perfect nesting
       select case (i)
       case(1)
         !ERROR: CYCLE statement to non-innermost associated loop of an OpenMP DO construct
diff --git a/flang/test/Semantics/OpenMP/do22.f90 b/flang/test/Semantics/OpenMP/do22.f90
index 818de56aa1093..2ced881a2af8b 100644
--- a/flang/test/Semantics/OpenMP/do22.f90
+++ b/flang/test/Semantics/OpenMP/do22.f90
@@ -4,9 +4,11 @@
 subroutine do_imperfectly_nested_before
   integer i, j
 
-  ! Valid: print is allowed as CLN intervening code with collapse
+  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
+  !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp do collapse(2)
   do i = 1, 10
+    !BECAUSE: This code prevents perfect nesting
     print *, i
     do j = 1, 10
       print *, i, j
@@ -19,134 +21,15 @@ subroutine do_imperfectly_nested_before
 subroutine do_imperfectly_nested_behind
   integer i, j
 
-  ! Valid: print is allowed as CLN intervening code with collapse
-  !$omp do collapse(2)
-  do i = 1, 10
-    do j = 1, 10
-      print *, i, j
-    end do
-    print *, i
-  end do
-  !$omp end do
-end subroutine
-
-
-subroutine do_imperfectly_nested_scalar_assign
-  integer i, j, x
-
-  ! Valid: scalar assignment is allowed as CLN intervening code with collapse
-  !$omp do collapse(2)
-  do i = 1, 10
-    x = i + 1
-    do j = 1, 10
-      print *, i, j, x
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-
-subroutine do_imperfectly_nested_call
-  integer i, j
-
-  ! Valid: subroutine call is allowed as CLN intervening code with collapse
-  !$omp do collapse(2)
-  do i = 1, 10
-    call sub(i)
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-
-subroutine do_imperfectly_nested_multiple
-  integer i, j, x
-
-  ! Valid: multiple scalar statements are allowed as CLN intervening code
-  !$omp do collapse(2)
-  do i = 1, 10
-    x = i * 2
-    print *, x
-    call sub(x)
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-
-subroutine do_imperfect_collapse_bare_ordered
-  integer i, j, x
-
-  ! Valid: bare ORDERED does not require a perfect nest.
-  !$omp do collapse(2) ordered
-  do i = 1, 10
-    x = 0
-    do j = 1, 10
-      !$omp ordered
-      print *, i, j, x
-      !$omp end ordered
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-
-subroutine do_imperfect_ordered_requires_perfect
-  integer i, j
-
-  ! ordered(2) still requires perfect nesting at default OpenMP version
   !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
-  !BECAUSE: ORDERED clause was specified with argument 2
-  !$omp do ordered(2)
-  do i = 1, 10
-    !BECAUSE: This code prevents perfect nesting
-    print *, i
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-
-subroutine do_imperfect_collapse_ordered_requires_perfect
-  integer i, j, k
-
-  ! collapse(2) ordered(3) requires perfect nesting at default OpenMP version because ordered(3) > collapse(2)
-  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 1
-  !BECAUSE: ORDERED clause was specified with argument 3
-  !$omp do collapse(2) ordered(3)
-  do i = 1, 10
-    !BECAUSE: This code prevents perfect nesting
-    print *, i
-    do j = 1, 10
-      do k = 1, 10
-        print *, i, j, k
-      end do
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-
-subroutine do_imperfect_array_assign_invalid
-  integer i, j
-  integer :: a(10)
-
-  ! Array assignment is invalid CLN intervening code
-  !ERROR: This construct requires a nest of depth 2, but the associated nest is a nest of depth 1
   !BECAUSE: COLLAPSE clause was specified with argument 2
   !$omp do collapse(2)
   do i = 1, 10
-    !BECAUSE: The nest contains code that prevents it from being canonical at this nesting level
-    a(:) = 0
     do j = 1, 10
       print *, i, j
     end do
+    !BECAUSE: This code prevents perfect nesting
+    print *, i
   end do
   !$omp end do
 end subroutine
diff --git a/flang/test/Semantics/OpenMP/doacross-nesting-omp60.f90 b/flang/test/Semantics/OpenMP/doacross-nesting-omp60.f90
deleted file mode 100644
index d11be5a60e072..0000000000000
--- a/flang/test/Semantics/OpenMP/doacross-nesting-omp60.f90
+++ /dev/null
@@ -1,148 +0,0 @@
-! RUN: %python %S/../test_errors.py %s %flang -fopenmp -fopenmp-version=60
-! OpenMP 6.0: doacross loop nests (those with ordered doacross(sink/source)
-! constructs) require perfect nesting.
-
-! ordered(2) without doacross directives: imperfect nesting is valid in 6.0.
-subroutine ordered_no_doacross_imperfect
-  integer i, j
-
-  !$omp do ordered(2)
-  do i = 1, 10
-    print *, i
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! Bare ORDERED (no argument) carries no doacross intent and does not require
-! perfect nesting.
-subroutine bare_ordered_no_doacross
-  integer i, j, x
-
-  !$omp do ordered
-  do i = 1, 10
-    x = 0
-    do j = 1, 10
-      !$omp ordered
-      print *, i, j, x
-      !$omp end ordered
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! Perfectly nested doacross: valid.
-subroutine doacross_perfect
-  integer i, j
-
-  !$omp do ordered(2)
-  do i = 1, 10
-    do j = 1, 10
-      !$omp ordered doacross(sink: i-1, j)
-      print *, i, j
-      !$omp ordered doacross(source)
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! Imperfectly nested doacross: invalid in 6.0.
-subroutine doacross_imperfect
-  integer i, j
-
-  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
-  !BECAUSE: ORDERED clause was specified with argument 2
-  !$omp do ordered(2)
-  do i = 1, 10
-    !BECAUSE: This code prevents perfect nesting
-    print *, i
-    do j = 1, 10
-      !$omp ordered doacross(sink: i-1, j)
-      print *, i, j
-      !$omp ordered doacross(source)
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! collapse(2) ordered(3) without doacross: imperfect nesting is valid.
-subroutine collapse_ordered_no_doacross_imperfect
-  integer i, j, k
-
-  !$omp do collapse(2) ordered(3)
-  do i = 1, 10
-    print *, i
-    do j = 1, 10
-      do k = 1, 10
-        print *, i, j, k
-      end do
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! Doacross with collapse: ordered(N) controls depth when N > collapse.
-subroutine doacross_collapse
-  integer i, j, k
-
-  !ERROR: This construct requires a perfect nest of depth 3, but the associated nest is a perfect nest of depth 1
-  !BECAUSE: ORDERED clause was specified with argument 3
-  !$omp do collapse(2) ordered(3)
-  do i = 1, 10
-    !BECAUSE: This code prevents perfect nesting
-    print *, i
-    do j = 1, 10
-      do k = 1, 10
-        !$omp ordered doacross(sink: i-1, j, k)
-        print *, i, j, k
-        !$omp ordered doacross(source)
-      end do
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! ORDERED with no argument: the number of doacross-affected loops defaults to
-! the COLLAPSE value (2 here). An imperfectly nested doacross is therefore
-! invalid, and the diagnostic is keyed off COLLAPSE rather than ORDERED.
-subroutine doacross_collapse_ordered_default
-  integer i, j
-
-  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
-  !BECAUSE: COLLAPSE clause was specified with argument 2
-  !$omp do collapse(2) ordered
-  do i = 1, 10
-    !BECAUSE: This code prevents perfect nesting
-    print *, i
-    do j = 1, 10
-      !$omp ordered doacross(sink: i-1, j)
-      print *, i, j
-      !$omp ordered doacross(source)
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! Doacross inside a nested OpenMP region should not force perfect nesting on
-! the outer loop. The doacross binds to the inner loop, not the outer one.
-subroutine doacross_in_nested_region
-  integer i, j, k
-
-  !$omp do collapse(2)
-  do i = 1, 10
-    print *, i
-    do j = 1, 10
-      !$omp parallel
-      !$omp do ordered(1)
-      do k = 1, 10
-        !$omp ordered doacross(source)
-        print *, k
-      end do
-      !$omp end do
-      !$omp end parallel
-    end do
-  end do
-  !$omp end do
-end subroutine
diff --git a/flang/test/Semantics/OpenMP/ordered-nesting-omp50.f90 b/flang/test/Semantics/OpenMP/ordered-nesting-omp50.f90
deleted file mode 100644
index f2b82c343cf9c..0000000000000
--- a/flang/test/Semantics/OpenMP/ordered-nesting-omp50.f90
+++ /dev/null
@@ -1,50 +0,0 @@
-! RUN: %python %S/../test_errors.py %s %flang -fopenmp -fopenmp-version=50
-! OpenMP 5.0: an ORDERED clause requires perfect nesting, whether or not the
-! clause has an argument. This is stricter than 5.1/5.2, where only ORDERED(n)
-! (with an argument) requires perfect nesting (see ordered-nesting-omp51.f90).
-
-! Bare ORDERED with COLLAPSE(2): the two associated loops must be perfectly
-! nested in 5.0, so intervening code between them is an error.
-subroutine bare_ordered_collapse_imperfect
-  integer i, j
-
-  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
-  !BECAUSE: COLLAPSE clause was specified with argument 2
-  !$omp do collapse(2) ordered
-  do i = 1, 10
-    !BECAUSE: This code prevents perfect nesting
-    print *, i
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! Bare ORDERED with COLLAPSE(2), perfectly nested: valid.
-subroutine bare_ordered_collapse_perfect
-  integer i, j
-
-  !$omp do collapse(2) ordered
-  do i = 1, 10
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! Bare ORDERED with no COLLAPSE: only one loop is associated (depth 1), so
-! perfect nesting is trivially satisfied and intervening code is allowed.
-subroutine bare_ordered_no_collapse
-  integer i, j
-
-  !$omp do ordered
-  do i = 1, 10
-    print *, i
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
diff --git a/flang/test/Semantics/OpenMP/ordered-nesting-omp51.f90 b/flang/test/Semantics/OpenMP/ordered-nesting-omp51.f90
deleted file mode 100644
index a5f282dbdcd24..0000000000000
--- a/flang/test/Semantics/OpenMP/ordered-nesting-omp51.f90
+++ /dev/null
@@ -1,36 +0,0 @@
-! RUN: %python %S/../test_errors.py %s %flang -fopenmp -fopenmp-version=51
-! OpenMP 5.1/5.2: only an ORDERED clause *with* an argument requires perfect
-! nesting. A bare ORDERED clause does not, unlike in 5.0 (see
-! ordered-nesting-omp50.f90).
-
-! Bare ORDERED with COLLAPSE(2), imperfectly nested: valid in 5.1, since the
-! bare ORDERED clause does not impose perfect nesting.
-subroutine bare_ordered_collapse_imperfect
-  integer i, j
-
-  !$omp do collapse(2) ordered
-  do i = 1, 10
-    print *, i
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine
-
-! ORDERED(2) with an argument still requires perfect nesting.
-subroutine ordered_arg_imperfect
-  integer i, j
-
-  !ERROR: This construct requires a perfect nest of depth 2, but the associated nest is a perfect nest of depth 1
-  !BECAUSE: ORDERED clause was specified with argument 2
-  !$omp do ordered(2)
-  do i = 1, 10
-    !BECAUSE: This code prevents perfect nesting
-    print *, i
-    do j = 1, 10
-      print *, i, j
-    end do
-  end do
-  !$omp end do
-end subroutine



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