[all-commits] [llvm/llvm-project] 53b346: [Driver] -gsplit-dwarf: Produce .dwo regardless of...

[Fangrui Song via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 53b34601abf1d48e8df210ab8127b16fd35e275a
      https://github.com/llvm/llvm-project/commit/53b34601abf1d48e8df210ab8127b16fd35e275a
  Author: Fangrui Song <i at maskray.me>
  Date:   2021-01-13 (Wed, 13 Jan 2021)

  Changed paths:
    M clang/lib/Driver/ToolChains/Clang.cpp
    M clang/test/Driver/split-debug.c

  Log Message:
  -----------
  [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

-g is an IR generation option while -gsplit-dwarf is an object file generation option.
For -gsplit-dwarf in the backend phase of a distributed ThinLTO (-fthinlto-index=) which does object file generation and no IR generation, -g should not be needed.

This patch makes `-fthinlto-index= -gsplit-dwarf` emit .dwo even in the absence of -g.
This should fix https://crbug.com/1158215 after D80391.

```
// Distributed ThinLTO usage
clang -g -O2 -c -flto=thin -fthin-link-bitcode=a.indexing.o a.c
clang -g -O2 -c -flto=thin -fthin-link-bitcode=b.indexing.o b.c
clang -fuse-ld=lld -Wl,--thinlto-index-only=a.rsp -Wl,--thinlto-prefix-replace=';lto/' -Wl,--thinlto-object-suffix-replace='.indexing.o;.o' a.indexing.o b.indexing.o
clang -gsplit-dwarf -O2 -c -fthinlto-index=lto/a.o.thinlto.bc a.o -o lto/a.o
clang -gsplit-dwarf -O2 -c -fthinlto-index=lto/b.o.thinlto.bc b.o -o lto/b.o
clang -fuse-ld=lld @a.rsp -o exe
```

Note: for implicit regular/Thin LTO, .dwo emission works without this patch:
`clang -flto=thin -gsplit-dwarf a.o b.o` passes `-plugin-opt=dwo_dir=` to the linker.
The linker forwards the option to LTO. LTOBackend.cpp emits `$dwo_dir/[01234].dwo`.

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D94647