InstCombine: Defensively avoid undefined shifts by limiting the amount to the bit...

No test case, undefined shifts get folded early, but can occur when other
transforms generate a constant. Thanks to Duncan for bringing this up.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162755 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 65a64b8..2119115 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -467,7 +467,7 @@ Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
     Value *X;
     ConstantInt *C1;
     if (match(Op0, m_LShr(m_Value(X), m_ConstantInt(C1)))) {
-      APInt NC = C2->getValue().shl(C1->getZExtValue());
+      APInt NC = C2->getValue().shl(C1->getLimitedValue(C1->getBitWidth()-1));
       return BinaryOperator::CreateUDiv(X, Builder->getInt(NC));
     }
   }
@@ -548,7 +548,7 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
     Value *X;
     ConstantInt *C1;
     if (match(Op0, m_AShr(m_Value(X), m_ConstantInt(C1)))) {
-      APInt NC = C2->getValue().shl(C1->getZExtValue());
+      APInt NC = C2->getValue().shl(C1->getLimitedValue(C1->getBitWidth()-1));
       return BinaryOperator::CreateSDiv(X, Builder->getInt(NC));
     }
   }