[InstCombine] Handle GEP inbounds in select op replacement (PR47730)

When retrying the "simplify with operand replaced" select
optimization without poison flags, also handle inbounds on GEPs.

Of course, this particular example would also be safe to transform
while keeping inbounds, but the underlying machinery does not
know this (yet).

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 087586e..2501c56 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1200,7 +1200,7 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
   // InstSimplify already performed this fold if it was possible subject to
   // current poison-generating flags. Try the transform again with
   // poison-generating flags temporarily dropped.
-  bool WasNUW = false, WasNSW = false, WasExact = false;
+  bool WasNUW = false, WasNSW = false, WasExact = false, WasInBounds = false;
   if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(FalseVal)) {
     WasNUW = OBO->hasNoUnsignedWrap();
     WasNSW = OBO->hasNoSignedWrap();
@@ -1211,6 +1211,10 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
     WasExact = PEO->isExact();
     FalseInst->setIsExact(false);
   }
+  if (auto *GEP = dyn_cast<GetElementPtrInst>(FalseVal)) {
+    WasInBounds = GEP->isInBounds();
+    GEP->setIsInBounds(false);
+  }
 
   // Try each equivalence substitution possibility.
   // We have an 'EQ' comparison, so the select's false value will propagate.
@@ -1230,6 +1234,8 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
     FalseInst->setHasNoSignedWrap();
   if (WasExact)
     FalseInst->setIsExact();
+  if (WasInBounds)
+    cast<GetElementPtrInst>(FalseInst)->setIsInBounds();
 
   return nullptr;
 }

diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 326050c..987f34e 100644 (file)
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -2725,12 +2725,11 @@ define i32 @select_replacement_loop2(i32 %arg, i32 %arg2) {
   ret i32 %sel
 }
 
+; TODO: Dropping the inbounds flag should not be necessary for this fold.
 define i8* @select_replacement_gep_inbounds(i8* %base, i64 %offset) {
 ; CHECK-LABEL: @select_replacement_gep_inbounds(
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[OFFSET:%.*]], 0
-; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, i8* [[BASE:%.*]], i64 [[OFFSET]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i8* [[BASE]], i8* [[GEP]]
-; CHECK-NEXT:    ret i8* [[SEL]]
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i8, i8* [[BASE:%.*]], i64 [[OFFSET:%.*]]
+; CHECK-NEXT:    ret i8* [[GEP]]
 ;
   %cmp = icmp eq i64 %offset, 0
   %gep = getelementptr inbounds i8, i8* %base, i64 %offset