[all-commits] [llvm/llvm-project] da9ca9: [flang][driver] Support Makefile dependency genera...

[Thirumalai Shaktivel via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: da9ca9c5aeb29e5c1f1bfc27c746d03da1e1974d
      https://github.com/llvm/llvm-project/commit/da9ca9c5aeb29e5c1f1bfc27c746d03da1e1974d
  Author: Thirumalai Shaktivel <74826228+Thirumalai-Shaktivel at users.noreply.github.com>
  Date:   2026-08-05 (Wed, 05 Aug 2026)

  Changed paths:
    M clang/include/clang/Basic/MakeSupport.h
    M clang/include/clang/Frontend/DependencyOutputOptions.h
    M clang/include/clang/Options/Options.td
    M clang/lib/Basic/MakeSupport.cpp
    M clang/lib/Driver/ToolChains/Flang.cpp
    M clang/lib/Frontend/DependencyFile.cpp
    M flang/docs/FlangDriver.md
    M flang/include/flang/Frontend/FrontendAction.h
    M flang/include/flang/Frontend/FrontendOptions.h
    M flang/include/flang/Parser/provenance.h
    M flang/lib/Frontend/CompilerInvocation.cpp
    M flang/lib/Frontend/FrontendAction.cpp
    M flang/lib/Parser/provenance.cpp
    A flang/test/Driver/dependency-file-gen-mod.f90
    A flang/test/Driver/dependency-file-gen.f90
    A flang/test/Driver/dependency-file.f90

  Log Message:
  -----------
  [flang][driver] Support Makefile dependency generation (#209379)

Implement the GCC/Clang dependency-file flags for flang, which it
previously rejected as unknown arguments: -M, -MM, -MD, -MMD, -MF,
-MT and -MQ.

Feature:
 -  -MD/-MMD : write a .d file alongside a normal compile
 -  -M/-MM   : run through semantics; emit deps to stdout by default
 -  -MF      : dependency-file path
 -  -MT/-MQ  : target name (verbatim / Make-quoted)
  (-M==-MM and -MD==-MMD; Fortran has no system/user header split.)

Design:
- `-M`/`-MM`: driver passes `-fsyntax-only -dependency-file - -MT
  <target>` to `-fc1`. Running through semantics resolves USE
  statements so module file dependencies are captured in the output.
  This deviates from clang's prescan-only behaviour for -M, but is
  intentional: unlike C/C++ #include, Fortran's USE statement is
  resolved at the semantic stage, not during preprocessing.

- `-MD`/`-MMD`: driver passes `-dependency-file foo.d -MT <target>`
  alongside the normal compile action. The object file is produced as
  usual, and the dependency file is written as a side effect.

- `-MF <path>` overrides where the dependency file is written.
  `-MT <target>` sets the target name (the part before the colon in
  the Make rule) verbatim. `-MQ` does the same but additionally
  quotes characters that are special to Make.

- In `-fc1`, `-dependency-file` and `-MT` are stored in the frontend
  options. After the action, `writeDependencyFile()` is called
  unconditionally. It collects every file opened during the action —
  the source plus all INCLUDE/#include/USE module files — via
  `GetIncludedFilePaths()`, then writes the
  `target: source includes...` Make rule to the specified file, or
  stdout if the path is `-`.



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