[llvm] 8f553da - [instsimplify] Add a comment and test for a highly confusing case

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2022-01-11T09:24:10-08:00
New Revision: 8f553da4926146e9ed64adebdc360c00b1076770

URL: https://github.com/llvm/llvm-project/commit/8f553da4926146e9ed64adebdc360c00b1076770
DIFF: https://github.com/llvm/llvm-project/commit/8f553da4926146e9ed64adebdc360c00b1076770.diff

LOG: [instsimplify] Add a comment and test for a highly confusing case

Added: 
    

Modified: 
    llvm/lib/Analysis/InstructionSimplify.cpp
    llvm/test/Transforms/InstSimplify/call.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 1ec5c4e9f6b54..0a3855f219275 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -2696,7 +2696,9 @@ computePointerICmp(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
 
     // Fold comparisons for non-escaping pointer even if the allocation call
     // cannot be elided. We cannot fold malloc comparison to null. Also, the
-    // dynamic allocation call could be either of the operands.
+    // dynamic allocation call could be either of the operands.  Note that
+    // the other operand can not be based on the alloc - if it were, then
+    // the cmp itself would be a capture.
     Value *MI = nullptr;
     if (isAllocLikeFn(LHS, TLI) &&
         llvm::isKnownNonZero(RHS, DL, 0, nullptr, CxtI, DT))

diff  --git a/llvm/test/Transforms/InstSimplify/call.ll b/llvm/test/Transforms/InstSimplify/call.ll
index a4560f84b6c7b..7aad90759d49d 100644
--- a/llvm/test/Transforms/InstSimplify/call.ll
+++ b/llvm/test/Transforms/InstSimplify/call.ll
@@ -1546,4 +1546,20 @@ define <3 x i33> @ctlz_ashr_sign_bit_vec(<3 x i33> %x) {
   ret <3 x i33> %r
 }
 
+declare i8* @llvm.ptrmask.p0i8.i64(i8* , i64)
+
+define i1 @capture_vs_recurse(i64 %mask) {
+; CHECK-LABEL: @capture_vs_recurse(
+; CHECK-NEXT:    [[A:%.*]] = call noalias i8* @malloc(i64 8)
+; CHECK-NEXT:    [[B:%.*]] = call nonnull i8* @llvm.ptrmask.p0i8.i64(i8* [[A]], i64 [[MASK:%.*]])
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8* [[A]], [[B]]
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %a = call noalias i8* @malloc(i64 8)
+  %b = call nonnull i8* @llvm.ptrmask.p0i8.i64(i8* %a, i64 %mask)
+  %cmp = icmp eq i8* %a, %b
+  ret i1 %cmp
+}
+
+
 attributes #0 = { nobuiltin readnone }