[PATCH] D140456: [SCEV] Help getLoopInvariantExitCondDuringFirstIterations deal with complex `umin` exit counts. PR59615

[Max Kazantsev via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG9a7286b61f61: [SCEV] Help getLoopInvariantExitCondDuringFirstIterations deal with complex… (authored by mkazantsev).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140456/new/

https://reviews.llvm.org/D140456

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Transforms/IndVarSimplify/X86/pr59615.ll


Index: llvm/test/Transforms/IndVarSimplify/X86/pr59615.ll
===================================================================
--- llvm/test/Transforms/IndVarSimplify/X86/pr59615.ll
+++ llvm/test/Transforms/IndVarSimplify/X86/pr59615.ll
@@ -8,35 +8,30 @@
 ; CHECK-LABEL: @test(
 ; CHECK-NEXT:  bb:
 ; CHECK-NEXT:    [[VAR:%.*]] = load atomic i32, ptr addrspace(1) poison unordered, align 8, !range [[RNG0:![0-9]+]], !invariant.load !1, !noundef !1
-; CHECK-NEXT:    [[VAR1:%.*]] = add nsw i32 [[VAR]], -1
 ; CHECK-NEXT:    [[VAR2:%.*]] = icmp eq i32 [[VAR]], 0
 ; CHECK-NEXT:    br i1 [[VAR2]], label [[BB18:%.*]], label [[BB19:%.*]]
 ; CHECK:       bb3:
 ; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ 0, [[BB19]] ], [ [[INDVARS_IV_NEXT:%.*]], [[BB12:%.*]] ]
-; CHECK-NEXT:    [[TMP0:%.*]] = sub nsw i64 [[TMP3:%.*]], [[INDVARS_IV]]
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[TMP0]] to i32
-; CHECK-NEXT:    [[VAR6:%.*]] = icmp ult i32 [[TMP1]], [[VAR]]
-; CHECK-NEXT:    br i1 [[VAR6]], label [[BB8:%.*]], label [[BB7:%.*]]
+; CHECK-NEXT:    br i1 true, label [[BB8:%.*]], label [[BB7:%.*]]
 ; CHECK:       bb7:
 ; CHECK-NEXT:    ret void
 ; CHECK:       bb8:
 ; CHECK-NEXT:    [[VAR9:%.*]] = load atomic i32, ptr addrspace(1) poison unordered, align 8, !range [[RNG0]], !invariant.load !1, !noundef !1
-; CHECK-NEXT:    [[TMP2:%.*]] = zext i32 [[VAR9]] to i64
-; CHECK-NEXT:    [[VAR10:%.*]] = icmp ult i64 [[INDVARS_IV]], [[TMP2]]
+; CHECK-NEXT:    [[TMP0:%.*]] = zext i32 [[VAR9]] to i64
+; CHECK-NEXT:    [[VAR10:%.*]] = icmp ult i64 [[INDVARS_IV]], [[TMP0]]
 ; CHECK-NEXT:    br i1 [[VAR10]], label [[BB12]], label [[BB11:%.*]]
 ; CHECK:       bb11:
 ; CHECK-NEXT:    ret void
 ; CHECK:       bb12:
 ; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
-; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[WIDE_TRIP_COUNT:%.*]]
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[TMP1:%.*]]
 ; CHECK-NEXT:    br i1 [[EXITCOND]], label [[BB3:%.*]], label [[BB17:%.*]]
 ; CHECK:       bb17:
 ; CHECK-NEXT:    unreachable
 ; CHECK:       bb18:
 ; CHECK-NEXT:    ret void
 ; CHECK:       bb19:
-; CHECK-NEXT:    [[TMP3]] = sext i32 [[VAR1]] to i64
-; CHECK-NEXT:    [[WIDE_TRIP_COUNT]] = zext i32 [[VAR]] to i64
+; CHECK-NEXT:    [[TMP1]] = zext i32 [[VAR]] to i64
 ; CHECK-NEXT:    br label [[BB3]]
 ;
 bb:
Index: llvm/lib/Analysis/ScalarEvolution.cpp
===================================================================
--- llvm/lib/Analysis/ScalarEvolution.cpp
+++ llvm/lib/Analysis/ScalarEvolution.cpp
@@ -11046,6 +11046,26 @@
 ScalarEvolution::getLoopInvariantExitCondDuringFirstIterations(
     ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
     const Instruction *CtxI, const SCEV *MaxIter) {
+  if (auto LIP = getLoopInvariantExitCondDuringFirstIterationsImpl(
+          Pred, LHS, RHS, L, CtxI, MaxIter))
+    return LIP;
+  if (auto *UMin = dyn_cast<SCEVUMinExpr>(MaxIter))
+    // Number of iterations expressed as UMIN isn't always great for expressing
+    // the value on the last iteration. If the straightforward approach didn't
+    // work, try the following trick: if the a predicate is invariant for X, it
+    // is also invariant for umin(X, ...). So try to find something that works
+    // among subexpressions of MaxIter expressed as umin.
+    for (auto *Op : UMin->operands())
+      if (auto LIP = getLoopInvariantExitCondDuringFirstIterationsImpl(
+              Pred, LHS, RHS, L, CtxI, Op))
+        return LIP;
+  return std::nullopt;
+}
+
+std::optional<ScalarEvolution::LoopInvariantPredicate>
+ScalarEvolution::getLoopInvariantExitCondDuringFirstIterationsImpl(
+    ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
+    const Instruction *CtxI, const SCEV *MaxIter) {
   // Try to prove the following set of facts:
   // - The predicate is monotonic in the iteration space.
   // - If the check does not fail on the 1st iteration:
Index: llvm/include/llvm/Analysis/ScalarEvolution.h
===================================================================
--- llvm/include/llvm/Analysis/ScalarEvolution.h
+++ llvm/include/llvm/Analysis/ScalarEvolution.h
@@ -1122,6 +1122,11 @@
                                                 const Instruction *CtxI,
                                                 const SCEV *MaxIter);
 
+  std::optional<LoopInvariantPredicate>
+  getLoopInvariantExitCondDuringFirstIterationsImpl(
+      ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
+      const Instruction *CtxI, const SCEV *MaxIter);
+
   /// Simplify LHS and RHS in a comparison with predicate Pred. Return true
   /// iff any changes were made. If the operands are provably equal or
   /// unequal, LHS and RHS are set to the same value and Pred is set to either


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