[all-commits] [llvm/llvm-project] 0fdfb6: [Flang] Add support to use LTO specific pipelines

[Usman Nadeem via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0fdfb65e2624aa151cb07a9c842331f7af9a21ca
      https://github.com/llvm/llvm-project/commit/0fdfb65e2624aa151cb07a9c842331f7af9a21ca
  Author: Nadeem, Usman <mnadeem at quicinc.com>
  Date:   2023-03-09 (Thu, 09 Mar 2023)

  Changed paths:
    M clang/include/clang/Driver/Options.td
    M clang/lib/Driver/ToolChains/Flang.cpp
    M flang/include/flang/Frontend/CodeGenOptions.def
    M flang/lib/Frontend/CompilerInvocation.cpp
    M flang/lib/Frontend/FrontendActions.cpp
    M flang/test/Driver/default-optimization-pipelines.f90
    M flang/test/Driver/driver-help-hidden.f90
    M flang/test/Driver/driver-help.f90
    A flang/test/Driver/lto-bc.f90
    A flang/test/Driver/lto-flags.f90

  Log Message:
  -----------
  [Flang] Add support to use LTO specific pipelines

Thin and full LTO modes use different pre-link pipelines compared to
regular compilation. This patch adds support for calling those pipelines.

This patch closely mimics Clang's implementation with the exception that I
changed the codegen option name from `PrepareForLTO` to `PrepareForFullLTO`
to be more precise.

With this patch:
  - Compilation for full LTO should be as we expect (except possibly
  missing optimizations enabled by module summaries which we do not
  produce yet).
  - thinLTO uses the correct prelink pipeline but will use the postlink
  backend for fullLTO due to missing metadata and summary in the llvm
  module. I have added a warning regarding this: `flang-new: warning: the
  option '-flto=thin' is a work in progress`.

Differential Revision: https://reviews.llvm.org/D142420

Change-Id: I6b94b775b5b8e93340e520c5cd4bf60834b2e209