[all-commits] [llvm/llvm-project] 6d6779: X86MCCodeEmitter: Work around gcc/value-range.cc b...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 6d67794d164ebeedbd287816e1541964fb5d6c99
      https://github.com/llvm/llvm-project/commit/6d67794d164ebeedbd287816e1541964fb5d6c99
  Author: Fangrui Song <i at maskray.me>
  Date:   2025-07-06 (Sun, 06 Jul 2025)

  Changed paths:
    M llvm/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp

  Log Message:
  -----------
  X86MCCodeEmitter: Work around gcc/value-range.cc bug in GCC 13.3.0

GCC 13.3.0 -O3 miscompiles the `getImmFixupKind` after commit
c20379198c7fb66b9514d21ae1e07b0705e3e6fa (-O2 is good), leading to spurious
unreachable failure.

```
% ninja -C /tmp/out/custom-gcc-13 llc && /tmp/out/custom-gcc-13/bin/llc llvm/test/CodeGen/X86/2008-08-06-RewriterBug.ll -mtriple=i686
ninja: Entering directory `/tmp/out/custom-gcc-13'
ninja: no work to do.
Unknown immediate size
UNREACHABLE executed at /home/ray/llvm/llvm/lib/Target/X86/MCTargetDesc/X86BaseInfo.h:904!
```

The latest releases/gcc-13 branch contains the fix
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109934#c6 , resolving this
miscompile.

`Desc.TSFlags` works around the bug.



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