hack.diff

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index c3e46c1fade..e11cdfa7d16 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -2110,6 +2110,8 @@ void LSRInstance::OptimizeShadowIV() {
     if (!AR) continue;
     if (IsSigned && !AR->hasNoSignedWrap()) continue;
     if (!IsSigned && !AR->hasNoUnsignedWrap()) continue;
+    // FIXME: the above logic may need revisiting; hasNoUnsignedWrap can be used
+    // in conjunction with signed inputs.
 
     Type *SrcTy = PH->getType();
     int Mantissa = DestTy->getFPMantissaWidth();
@@ -3249,6 +3251,19 @@ void LSRInstance::CollectFixupsAndInitialFormulae() {
     User::op_iterator UseI =
         find(UserInst->operands(), U.getOperandValToReplace());
     assert(UseI != UserInst->op_end() && "cannot find IV operand");
+
+    // pnk: This may be where I should add the check if the input uses nsw/nuw
+    if (auto *BinOp = dyn_cast<OverflowingBinaryOperator>(UserInst)) {
+        if (BinOp->hasNoUnsignedWrap() || BinOp->hasNoSignedWrap()) {
+            LLVM_DEBUG(dbgs() << "Use: " << **UseI << " has no-wrap flags; discard\n");
+            continue;
+        } else {
+            LLVM_DEBUG(dbgs() << "Use: " << **UseI << " has no no-wrap flags\n");
+        }
+    } else {
+        LLVM_DEBUG(dbgs() << "Use: " << **UseI << " is not an overflowing binop\n");
+    }
+
     if (IVIncSet.count(UseI)) {
       LLVM_DEBUG(dbgs() << "Use is in profitable chain: " << **UseI << '\n');
       continue;