[all-commits] [llvm/llvm-project] 9d117e: Define __GCC_HAVE_DWARF2_CFI_ASM if applicable

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 9d117e7b2a399a9b2bcf53fb9b9c0946e82dc75c
      https://github.com/llvm/llvm-project/commit/9d117e7b2a399a9b2bcf53fb9b9c0946e82dc75c
  Author: Fangrui Song <i at maskray.me>
  Date:   2021-03-09 (Tue, 09 Mar 2021)

  Changed paths:
    M clang/lib/Driver/ToolChains/Clang.cpp
    A clang/test/Preprocessor/unwind-tables.c

  Log Message:
  -----------
  Define __GCC_HAVE_DWARF2_CFI_ASM if applicable

In -fno-exceptions -fno-asynchronous-unwind-tables -g0 mode,
GCC does not emit `.cfi_*` directives.

```
% diff <(gcc -fno-asynchronous-unwind-tables -dM -E a.c) <(gcc -dM -E a.c)
130a131
> #define __GCC_HAVE_DWARF2_CFI_ASM 1
```

This macro is useful because code can decide whether inline asm should include `.cfi_*` directives.
`.cfi_*` directives without `.cfi_startproc` can cause assembler errors
(integrated assembler: `this directive must appear between .cfi_startproc and .cfi_endproc directives`).

Differential Revision: https://reviews.llvm.org/D97743