InstCombine: Propagate exact in (udiv (lshr X,C1),C2) -> (udiv x,C1<<C2)

llvm-svn: 222620

1 files changed, 7 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 010625a..2befe19 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -997,9 +997,14 @@ Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
         match(Op1, m_APInt(C2))) {
       bool Overflow;
       APInt C2ShlC1 = C2->ushl_ov(*C1, Overflow);
-      if (!Overflow)
-        return BinaryOperator::CreateUDiv(
+      if (!Overflow) {
+        bool IsExact = I.isExact() && match(Op0, m_Exact(m_Value()));
+        BinaryOperator *BO = BinaryOperator::CreateUDiv(
             X, ConstantInt::get(X->getType(), C2ShlC1));
+        if (IsExact)
+          BO->setIsExact();
+        return BO;
+      }
     }
   }