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@gmail.com>
                         <evgeny.v.stupachenko@intel.com>
llvm-svn: 326861

2 files changed, 22 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/NaryReassociate.cpp b/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
index b026c8d692c..243d7fefb67 100644
--- a/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/NaryReassociate.cpp
@@ -429,6 +429,9 @@ NaryReassociatePass::tryReassociateGEPAtIndex(GetElementPtrInst *GEP,
 
 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))
diff --git a/llvm/test/Transforms/NaryReassociate/pr35710.ll b/llvm/test/Transforms/NaryReassociate/pr35710.ll
new file mode 100644
index 00000000000..f46dd27607e
--- /dev/null
+++ b/llvm/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
+}