InstCombine: Propagate exact for (sdiv -X, C) -> (sdiv X, -C)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222623 91177308-0d34-0410-b5e6-96231b3b80d8
bgamari · Nov 22, 2014 · 91349ee · 91349ee
1 parent 53a43d3
commit 91349ee
Show file tree

Hide file tree

Showing 2 changed files with 15 additions and 4 deletions.
diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1082,10 +1082,12 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
       return new ZExtInst(Builder->CreateICmpEQ(Op0, Op1), I.getType());
 
     // -X/C  -->  X/-C  provided the negation doesn't overflow.
-    if (SubOperator *Sub = dyn_cast<SubOperator>(Op0))
-      if (match(Sub->getOperand(0), m_Zero()) && Sub->hasNoSignedWrap())
-        return BinaryOperator::CreateSDiv(Sub->getOperand(1),
-                                          ConstantExpr::getNeg(RHS));
+    Value *X;
+    if (match(Op0, m_NSWSub(m_Zero(), m_Value(X)))) {
+      auto *BO = BinaryOperator::CreateSDiv(X, ConstantExpr::getNeg(RHS));
+      BO->setIsExact(I.isExact());
+      return BO;
+    }
   }
 
   // If the sign bits of both operands are zero (i.e. we can prove they are

diff --git a/test/Transforms/InstCombine/div.ll b/test/Transforms/InstCombine/div.ll
@@ -295,3 +295,12 @@ define <2 x i64> @test33(<2 x i64> %x) nounwind {
 ; CHECK-NEXT: udiv exact <2 x i64> %x, <i64 192, i64 192>
 ; CHECK-NEXT: ret <2 x i64>
 }
+
+define <2 x i64> @test34(<2 x i64> %x) nounwind {
+  %neg = sub nsw <2 x i64> zeroinitializer, %x
+  %div = sdiv exact <2 x i64> %neg, <i64 3, i64 4>
+  ret <2 x i64> %div
+; CHECK-LABEL: @test34(
+; CHECK-NEXT: sdiv exact <2 x i64> %x, <i64 -3, i64 -4>
+; CHECK-NEXT: ret <2 x i64>
+}