[PATCH] D144859: [LoopPredication] Account for critical edges when inserting assumes. PR26496

[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 rGa18ce47a3e00: [LoopPredication] Account for critical edges when inserting assumes. PR26496 (authored by mkazantsev).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D144859/new/

https://reviews.llvm.org/D144859

Files:
  llvm/lib/Transforms/Scalar/LoopPredication.cpp
  llvm/test/Transforms/LoopPredication/pr61022.ll


Index: llvm/test/Transforms/LoopPredication/pr61022.ll
===================================================================
--- llvm/test/Transforms/LoopPredication/pr61022.ll
+++ llvm/test/Transforms/LoopPredication/pr61022.ll
@@ -1,13 +1,36 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -S -passes=loop-predication < %s 2>&1 | FileCheck %s
-; REQUIRES: asserts
-; XFAIL: *
 
 declare void @llvm.experimental.deoptimize.isVoid(...)
 
-; FIXME: Loop predication here inserts assume across the critical edge, and
-; it leads to malformed IR (assume's condition does not dominate it).
 define void @test_01(i1 %cond) {
-; CHECK-LABEL: test
+; CHECK-LABEL: @test_01(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[INST:%.*]] = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    [[TMP0:%.*]] = and i1 true, [[INST]]
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       unreached:
+; CHECK-NEXT:    unreachable
+; CHECK:       loop:
+; CHECK-NEXT:    [[INST3:%.*]] = phi i32 [ 0, [[BB:%.*]] ], [ [[INST4:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    [[INST4]] = add nsw i32 [[INST3]], 1
+; CHECK-NEXT:    br i1 [[COND:%.*]], label [[BACKEDGE]], label [[GUARD_BLOCK:%.*]]
+; CHECK:       normal_ret:
+; CHECK-NEXT:    ret void
+; CHECK:       backedge:
+; CHECK-NEXT:    [[ASSUME_COND:%.*]] = phi i1 [ [[INST9:%.*]], [[GUARD_BLOCK]] ], [ true, [[LOOP]] ]
+; CHECK-NEXT:    call void @llvm.assume(i1 [[ASSUME_COND]])
+; CHECK-NEXT:    [[INST7:%.*]] = icmp sgt i32 [[INST3]], 137
+; CHECK-NEXT:    br i1 [[INST7]], label [[UNREACHED:%.*]], label [[LOOP]]
+; CHECK:       guard_block:
+; CHECK-NEXT:    [[INST9]] = icmp ult i32 [[INST4]], 10000
+; CHECK-NEXT:    br i1 [[TMP0]], label [[BACKEDGE]], label [[DEOPT:%.*]]
+; CHECK:       deopt:
+; CHECK-NEXT:    call void (...) @llvm.experimental.deoptimize.isVoid(i32 13) [ "deopt"() ]
+; CHECK-NEXT:    ret void
+; CHECK:       done:
+; CHECK-NEXT:    ret void
+;
 bb:
   %inst = call i1 @llvm.experimental.widenable.condition()
   br label %loop
Index: llvm/lib/Transforms/Scalar/LoopPredication.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopPredication.cpp
+++ llvm/lib/Transforms/Scalar/LoopPredication.cpp
@@ -863,7 +863,19 @@
   BI->setCondition(AllChecks);
   if (InsertAssumesOfPredicatedGuardsConditions) {
     Builder.SetInsertPoint(IfTrueBB, IfTrueBB->getFirstInsertionPt());
-    Builder.CreateAssumption(Cond);
+    // If this block has other predecessors, we might not be able to use Cond.
+    // In this case, create a Phi where every other input is `true` and input
+    // from guard block is Cond.
+    Value *AssumeCond = Cond;
+    if (!IfTrueBB->getUniquePredecessor()) {
+      auto *GuardBB = BI->getParent();
+      auto *PN = Builder.CreatePHI(Cond->getType(), pred_size(IfTrueBB),
+                                   "assume.cond");
+      for (auto *Pred : predecessors(IfTrueBB))
+        PN->addIncoming(Pred == GuardBB ? Cond : Builder.getTrue(), Pred);
+      AssumeCond = PN;
+    }
+    Builder.CreateAssumption(AssumeCond);
   }
   RecursivelyDeleteTriviallyDeadInstructions(OldCond, nullptr /* TLI */, MSSAU);
   assert(isGuardAsWidenableBranch(BI) &&


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