[LSR] Check for signed overflow in NarrowSearchSpaceByDetectingSupersets.

We are adding a sign extended IR value to an int64_t, which can cause
signed overflows, as in the attached test case, where we have a formula
with BaseOffset = -1 and a constant with numeric_limits<int64_t>::min().

If the addition would overflow, skip the simplification for this
formula. Note that the target triple is required to trigger the failure.

Reviewers: qcolombet, gilr, kparzysz, efriedma

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D59211

llvm-svn: 356256

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index e4b9c44ea84..340f5db4bdb 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -4423,7 +4423,9 @@ void LSRInstance::NarrowSearchSpaceByDetectingSupersets() {
              I = F.BaseRegs.begin(), E = F.BaseRegs.end(); I != E; ++I) {
           if (const SCEVConstant *C = dyn_cast<SCEVConstant>(*I)) {
             Formula NewF = F;
-            NewF.BaseOffset += C->getValue()->getSExtValue();
+            //FIXME: Formulas should store bitwidth to do wrapping properly.
+            //       See PR41034.
+            NewF.BaseOffset += (uint64_t)C->getValue()->getSExtValue();
             NewF.BaseRegs.erase(NewF.BaseRegs.begin() +
                                 (I - F.BaseRegs.begin()));
             if (LU.HasFormulaWithSameRegs(NewF)) {