https://bugs.llvm.org/show_bug.cgi?id=48209
Bug ID: 48209
Summary: Incorrect propagation of noalias metadata in
InlineFunction.
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Transformation Utilities
Assignee: unassignedb...@nondot.org
Reporter: x...@google.com
CC: llvm-bugs@lists.llvm.org, x...@google.com
Created attachment 24177
--> https://bugs.llvm.org/attachment.cgi?id=24177&action=edit
A test that shows we get undef code
commit 27f647d117087ca11959e232e6443f4aee31e966
[Inliner] Consistently apply callsite noalias metadata
seg-faults one of the our programs.
I'm not sure if the patch is correct -- it propagates the noalias metadata
from the callsite to the argument definition.
In our program, the argument definition defines the same alias.scope. The patch
will append !noalias metadata to the instruction with the same set of
!alias.scope.
We get:
%27 = load %"class.std::__cfi::__shared_weak_count"*,
%"class.std::__cfi::__shared_weak_count"** %26, align 8, !alias.scope !46635,
!noalias !46635
This is problematic. For this particular case, this load depends on a memset
which has the same alias group. With the noalias metadata added, alias query
skips the memory, and the dependent instruction becomes the memory allocation.
GVN has a rule that simplifies direct load the memory allocation to undef. The
generated code seg-faults.
I'm attaching a simplified test here.
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