[PATCH] D41467: PR35710: Nary reassociation falls into infinite loop

[Evgeny Stupachenko via Phabricator via llvm-commits]

evstupac updated this revision to Diff 133671.
evstupac added a comment.

Leave only zero check and move it to an earlier stage.


Repository:
  rL LLVM

https://reviews.llvm.org/D41467

Files:
  lib/Transforms/Scalar/NaryReassociate.cpp
  test/Transforms/NaryReassociate/pr35710.ll


Index: lib/Transforms/Scalar/NaryReassociate.cpp
===================================================================
--- lib/Transforms/Scalar/NaryReassociate.cpp
+++ lib/Transforms/Scalar/NaryReassociate.cpp
@@ -429,6 +429,9 @@
 
 Instruction *NaryReassociatePass::tryReassociateBinaryOp(BinaryOperator *I) {
   Value *LHS = I->getOperand(0), *RHS = I->getOperand(1);
+  // There is no need to reassociate 0.
+  if (SE->getSCEV(I)->isZero())
+    return nullptr;
   if (auto *NewI = tryReassociateBinaryOp(LHS, RHS, I))
     return NewI;
   if (auto *NewI = tryReassociateBinaryOp(RHS, LHS, I))
Index: test/Transforms/NaryReassociate/pr35710.ll
===================================================================
--- test/Transforms/NaryReassociate/pr35710.ll
+++ test/Transforms/NaryReassociate/pr35710.ll
@@ -0,0 +1,19 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -nary-reassociate -S | FileCheck %s
+
+; The test check that compilation does not fall into infinite loop.
+
+define i8 @foo(i8 %v) local_unnamed_addr #0 {
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:  region.0:
+; CHECK-NEXT:    [[TMP0:%.*]] = mul nsw i8 16, [[V:%.*]]
+; CHECK-NEXT:    [[TMP1:%.*]] = mul nsw i8 0, [[TMP0]]
+; CHECK-NEXT:    [[TMP2:%.*]] = mul nsw i8 1, [[TMP1]]
+; CHECK-NEXT:    ret i8 [[TMP2]]
+;
+region.0:
+  %0 = mul nsw i8 16, %v
+  %1 = mul nsw i8 0, %0
+  %2 = mul nsw i8 1, %1
+  ret i8 %2
+}


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