[PATCH] D68706: [InstCombine] don't assume 'inbounds' for bitcast deref or null pointer in non-default address space

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: lebedev.ri, nlopes, jdoerfert.
Herald added subscribers: hiraditya, mcrosier.
Herald added a project: LLVM.

Follow-up to D68244 <https://reviews.llvm.org/D68244> to account for a corner case discussed in:
https://bugs.llvm.org/show_bug.cgi?id=43501

Add one more restriction: if the pointer is deref-or-null and in a non-default (non-zero) address space, we can't assume inbounds.


https://reviews.llvm.org/D68706

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/load-bitcast-vec.ll


Index: llvm/test/Transforms/InstCombine/load-bitcast-vec.ll
===================================================================
--- llvm/test/Transforms/InstCombine/load-bitcast-vec.ll
+++ llvm/test/Transforms/InstCombine/load-bitcast-vec.ll
@@ -89,11 +89,11 @@
   ret float %r
 }
 
-; TODO: Is a null pointer inbounds in any address space?
+; A null pointer can't be assumed inbounds in a non-default address space.
 
 define float @matching_scalar_smallest_deref_or_null_addrspace(<4 x float> addrspace(4)* dereferenceable_or_null(1) %p) {
 ; CHECK-LABEL: @matching_scalar_smallest_deref_or_null_addrspace(
-; CHECK-NEXT:    [[BC:%.*]] = getelementptr inbounds <4 x float>, <4 x float> addrspace(4)* [[P:%.*]], i64 0, i64 0
+; CHECK-NEXT:    [[BC:%.*]] = getelementptr <4 x float>, <4 x float> addrspace(4)* [[P:%.*]], i64 0, i64 0
 ; CHECK-NEXT:    [[R:%.*]] = load float, float addrspace(4)* [[BC]], align 16
 ; CHECK-NEXT:    ret float [[R]]
 ;
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2344,8 +2344,12 @@
       // If the source pointer is dereferenceable, then assume it points to an
       // allocated object and apply "inbounds" to the GEP.
       bool CanBeNull;
-      if (Src->getPointerDereferenceableBytes(DL, CanBeNull))
-        GEP->setIsInBounds();
+      if (Src->getPointerDereferenceableBytes(DL, CanBeNull)) {
+        // In a non-default address space (not 0), a null pointer can not be
+        // assumed inbounds, so ignore that case (dereferenceable_or_null).
+        if (SrcPTy->getAddressSpace() == 0 || !CanBeNull)
+          GEP->setIsInBounds();
+      }
       return GEP;
     }
   }


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