[all-commits] [llvm/llvm-project] fcb7b3: [clang] Don't add DWARF debug info when assembling...

[Martin Storsjö via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: fcb7b390ccd5b4cfc71f13b5e16a846f3f400c10
      https://github.com/llvm/llvm-project/commit/fcb7b390ccd5b4cfc71f13b5e16a846f3f400c10
  Author: Martin Storsjö <martin at martin.st>
  Date:   2024-09-03 (Tue, 03 Sep 2024)

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

  Log Message:
  -----------
  [clang] Don't add DWARF debug info when assembling .s with clang-cl /Z7 (#106686)

This fixes a regression from f58330cbe44598eb2de0cca3b812f67fea0a71ca.

That commit changed the clang-cl options /Zi and /Z7 to be implemented
as aliases of -g rather than having separate handling.

This had the unintended effect, that when assembling .s files with
clang-cl, the /Z7 option (which implies using CodeView debug info) was
treated as a -g option, which causes `ClangAs::ConstructJob` to pick up
the option as part of `Args.getLastArg(options::OPT_g_Group)`, which
sets the `WantDebug` variable.

Within `Clang::ConstructJob`, we check for whether explicit `-gdwarf` or
`-gcodeview` options have been set, and if not, we pick the default
debug format for the current toolchain. However, in `ClangAs`, if debug
info has been enabled, it always adds DWARF debug info.

Add similar logic in `ClangAs` - check if the user has explicitly
requested either DWARF or CodeView, otherwise look up the toolchain
default. If we (either implicitly or explicitly) should be producing
CodeView, don't enable the default `ClangAs` DWARF generation.

This fixes the issue, where assembling a single `.s` file with clang-cl,
with the /Z7 option, causes the file to contain some DWARF sections.
This causes the output executable to contain DWARF, in addition to the
separate intended main PDB file.

By having the output executable contain DWARF sections, LLDB only looks
at the (very little) DWARF info in the executable, rather than looking
for a separate standalone PDB file. This caused an issue with LLDB's
tests, https://github.com/llvm/llvm-project/issues/101710.



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