https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120903
Bug ID: 120903
Summary: Alias information not used to optimize out
hand-written buffer aliasing checks
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: alias, missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: sjames at gcc dot gnu.org
Target Milestone: ---
Created attachment 61771
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61771&action=edit
test.c
Mirror version of https://github.com/llvm/llvm-project/issues/146401
"""
Clang (and GCC) don't seem to recognize the __fh_overlap macro in
godbolt.org/z/EqjKe716r as a buffer aliasing check.
The sample was adapted from jvoisin/fortify-headers@master/include/string.h,
which is reportedly used in Musl-based Linux distributions like Alpine.
In this case, since r was just allocated, the compiler should be able to reason
that r cannot overlap with a and delete the __fh_overlap check. It's also
important to be able to optimize this because memcpy is the usual pattern to
load memory without tripping strict aliasing issues.
"""
