[llvm] r326861 - Add early exit on reassociation of 0 expression.

[Evgeny Stupachenko via llvm-commits]

Author: evstupac
Date: Tue Mar  6 18:17:08 2018
New Revision: 326861

URL: http://llvm.org/viewvc/llvm-project?rev=326861&view=rev
Log:
Add early exit on reassociation of 0 expression.

Summary:

Before the patch a try to reassociate ((v * 16) * 0) * 1 fall into infinite loop

Reviewers: pankajchawla

Differential Revision: http://reviews.llvm.org/D41467

From: Evgeny Stupachenko <evstupac at gmail.com>
                         <evgeny.v.stupachenko at intel.com>

Added:
    llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp?rev=326861&r1=326860&r2=326861&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/NaryReassociate.cpp Tue Mar  6 18:17:08 2018
@@ -429,6 +429,9 @@ NaryReassociatePass::tryReassociateGEPAt
 
 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))

Added: llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll?rev=326861&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll (added)
+++ llvm/trunk/test/Transforms/NaryReassociate/pr35710.ll Tue Mar  6 18:17:08 2018
@@ -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
+}