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

llvm-svn: 222620

2 files changed, 16 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 010625a7157..2befe1934f4 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;
+      }
     }
   }
 
diff --git a/llvm/test/Transforms/InstCombine/div.ll b/llvm/test/Transforms/InstCombine/div.ll
index 5af86680697..585b04a4d5d 100644
--- a/llvm/test/Transforms/InstCombine/div.ll
+++ b/llvm/test/Transforms/InstCombine/div.ll
@@ -286,3 +286,12 @@ define i32 @test32(i32 %a, i32 %b) {
 ; CHECK-NEXT: %[[div:.*]] = udiv i32 %a, %[[shr]]
 ; CHECK-NEXT: ret i32
 }
+
+define <2 x i64> @test33(<2 x i64> %x) nounwind {
+  %shr = lshr exact <2 x i64> %x, <i64 5, i64 5>
+  %div = udiv exact <2 x i64> %shr, <i64 6, i64 6>
+  ret <2 x i64> %div
+; CHECK-LABEL: @test33(
+; CHECK-NEXT: udiv exact <2 x i64> %x, <i64 192, i64 192>
+; CHECK-NEXT: ret <2 x i64>
+}