[all-commits] [llvm/llvm-project] 171199: [Clang][CodeGen] Do not set inbounds flag for stru...

[Yingwei Zheng via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1711996805c506f5717193aaeedf3752dfdd900d
      https://github.com/llvm/llvm-project/commit/1711996805c506f5717193aaeedf3752dfdd900d
  Author: Yingwei Zheng <dtcxzyw2333 at gmail.com>
  Date:   2025-04-11 (Fri, 11 Apr 2025)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/CodeGen/CGExpr.cpp
    M clang/lib/CodeGen/CodeGenFunction.h
    M clang/test/CodeGen/catch-nullptr-and-nonzero-offset-in-offsetof-idiom.c
    M clang/test/CodeGenCXX/catch-nullptr-and-nonzero-offset-in-offsetof-idiom.cpp

  Log Message:
  -----------
  [Clang][CodeGen] Do not set inbounds flag for struct GEP with null base pointers (#130734)

In the LLVM middle-end we want to fold `gep inbounds null, idx -> null`:
https://alive2.llvm.org/ce/z/5ZkPx-
This pattern is common in real-world programs
(https://github.com/dtcxzyw/llvm-opt-benchmark/pull/55#issuecomment-1870963906).
Generally, it exists in some (actually) unreachable blocks, which is
introduced by JumpThreading.

However, some old-style offsetof macros are still widely used in
real-world C/C++ code (e.g., hwloc/slurm/luajit). To avoid breaking
existing code and inconvenience to downstream users, this patch removes
the inbounds flag from the struct gep if the base pointer is null.



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