InstCombine: Respect recursion depth in visitUDivOperand

[oota-llvm.git] / lib / Transforms / InstCombine / InstCombineSimplifyDemanded.cpp

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 1b42d3d504a3d57dbceb54729c0c59b9e6eac159..f0c96bdf76838b9db3c52b196f784286fb8c6971 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -43,6 +43,20 @@ static bool ShrinkDemandedConstant(Instruction *I, unsigned OpNo,
   // This instruction is producing bits that are not demanded. Shrink the RHS.
   Demanded &= OpC->getValue();
   I->setOperand(OpNo, ConstantInt::get(OpC->getType(), Demanded));
+
+  // If either 'nsw' or 'nuw' is set and the constant is negative,
+  // removing *any* bits from the constant could make overflow occur.
+  // Remove 'nsw' and 'nuw' from the instruction in this case.
+  if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(I)) {
+    assert(OBO->getOpcode() == Instruction::Add);
+    if (OBO->hasNoSignedWrap() || OBO->hasNoUnsignedWrap()) {
+      if (OpC->getValue().isNegative()) {
+        cast<BinaryOperator>(OBO)->setHasNoSignedWrap(false);
+        cast<BinaryOperator>(OBO)->setHasNoUnsignedWrap(false);
+      }
+    }
+  }
+
   return true;
 }