[PATCH] D95088: [InstCombine] avoid crashing on attribute propagation

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: jdoerfert, zequanwu, fhahn.
Herald added subscribers: hiraditya, mcrosier.
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In https://llvm.org/PR48810 , we are crashing while trying to propagate attributes from `mempcpy` (returns void*)  to `memcpy` (returns nothing - void).
We can avoid the crash by removing known incompatible attributes for the void return type.
I'm not sure if this goes far enough (should we just drop all attributes since this isn't the same function?). We also need to audit other transforms in LibCallSimplifier to make sure there are no other cases that have the same problem.


https://reviews.llvm.org/D95088

Files:
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/mempcpy.ll


Index: llvm/test/Transforms/InstCombine/mempcpy.ll
===================================================================
--- llvm/test/Transforms/InstCombine/mempcpy.ll
+++ llvm/test/Transforms/InstCombine/mempcpy.ll
@@ -53,4 +53,15 @@
   ret i8* %r
 }
 
+; The original call may have attributes that can not propagate to memcpy.
+
+define i32 @PR48810() {
+; CHECK-LABEL: @PR48810(
+; CHECK-NEXT:    call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 1 undef, i8* align 536870912 null, i64 undef, i1 false)
+; CHECK-NEXT:    ret i32 undef
+;
+  %r = call dereferenceable(1) i8* @mempcpy(i8* undef, i8* null, i64 undef)
+  ret i32 undef
+}
+
 declare i8* @mempcpy(i8*, i8* nocapture readonly, i64)
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1150,7 +1150,11 @@
   // mempcpy(x, y, n) -> llvm.memcpy(align 1 x, align 1 y, n), x + n
   CallInst *NewCI =
       B.CreateMemCpy(Dst, Align(1), CI->getArgOperand(1), Align(1), N);
+  // Propagate attributes, but memcpy has no return value, so make sure that
+  // any return attributes are compliant.
   NewCI->setAttributes(CI->getAttributes());
+  NewCI->removeAttributes(AttributeList::ReturnIndex,
+                          AttributeFuncs::typeIncompatible(NewCI->getType()));
   return B.CreateInBoundsGEP(B.getInt8Ty(), Dst, N);
 }
 


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