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llvm / llvm-project / 26f97ee9aa413db240c397f96ddd5b0553a57d30
commit26f97ee9aa413db240c397f96ddd5b0553a57d30[log] [tgz]
authorNuko Y. <or@dmc.chat>Mon May 12 22:10:28 2025 +0000
committerGitHub <noreply@github.com>Mon May 12 15:10:28 2025 -0700
treeae7c176eb0141e41c05e17d5eb7f4c998fc7da16
parent64082912a500d004c53ad1b3425098b495572663 [diff]
[AArch64] Stop reserved registers from being saved in prolog/epilog (#138448)

[GCC's
documentation](https://gcc.gnu.org/onlinedocs/gcc-15.1.0/gcc/Code-Gen-Options.html)
is clear on how -ffixed-reg must behave:
```
  Treat the register named reg as a fixed register; generated
  code should never refer to it (except perhaps as a stack pointer,
  frame pointer or in some other fixed role).
```

This implies prolog/epilog code also must not save/restore explicitly
fixed registers, even when it is callee-saved. Some projects rely on
this (GCC's) behavior.

For example,
```
void f() {
  register uint64_t x28 asm("x28") = 0xee;
  asm volatile("" : "+r"(x28)); // avoid mov being eliminated
}
```
should not touch x28 outside of `mov w28,#0xee`.

For riscv64, clang behaves the same as GCC, so I am inclined to believe
this is indeed a bug.

Fixes #111379.
5 files changed
tree: ae7c176eb0141e41c05e17d5eb7f4c998fc7da16
  1. .ci/
  2. .github/
  3. bolt/
  4. clang/
  5. clang-tools-extra/
  6. cmake/
  7. compiler-rt/
  8. cross-project-tests/
  9. flang/
  10. flang-rt/
  11. libc/
  12. libclc/
  13. libcxx/
  14. libcxxabi/
  15. libunwind/
  16. lld/
  17. lldb/
  18. llvm/
  19. llvm-libgcc/
  20. mlir/
  21. offload/
  22. openmp/
  23. polly/
  24. pstl/
  25. runtimes/
  26. third-party/
  27. utils/
  28. .clang-format
  29. .clang-format-ignore
  30. .clang-tidy
  31. .git-blame-ignore-revs
  32. .gitattributes
  33. .gitignore
  34. .mailmap
  35. CODE_OF_CONDUCT.md
  36. CONTRIBUTING.md
  37. LICENSE.TXT
  38. pyproject.toml
  39. README.md
  40. SECURITY.md
README.md

The LLVM Compiler Infrastructure

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Welcome to the LLVM project!

This repository contains the source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and run-time environments.

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