Fix an overly general check in SimplifyIndvar to handle useless phi cycles.

The right way to check for a binary operation is
cast<BinaryOperator>. The original check: cast<Instruction> &&
numOperands() == 2 would match phi "instructions", leading to an
infinite loop in extreme corner case: a useless phi with operands
[self, constant] that prior optimization passes failed to remove,
being used in the loop by another useless phi, in turn being used by an
lshr or udiv.

Fixes PR11350: runaway iteration assertion.

llvm-svn: 144935

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 76289c055b9..6732a789d5f 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -107,8 +107,8 @@ Value *SimplifyIndvar::foldIVUser(Instruction *UseInst, Instruction *IVOperand)
 
     // Attempt to fold a binary operator with constant operand.
     // e.g. ((I + 1) >> 2) => I >> 2
-    if (IVOperand->getNumOperands() != 2 ||
-        !isa<ConstantInt>(IVOperand->getOperand(1)))
+    if (!isa<BinaryOperator>(IVOperand)
+        || !isa<ConstantInt>(IVOperand->getOperand(1)))
       return 0;
 
     IVSrc = IVOperand->getOperand(0);