[all-commits] [llvm/llvm-project] 2a551a: [Multilib] Add -fmultilib-flag command-line option...

[Victor Campos via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2a551ab3002897ba52a27961b766f3741695c816
      https://github.com/llvm/llvm-project/commit/2a551ab3002897ba52a27961b766f3741695c816
  Author: Victor Campos <victor.campos at arm.com>
  Date:   2025-01-13 (Mon, 13 Jan 2025)

  Changed paths:
    M clang/include/clang/Driver/Options.td
    M clang/lib/Driver/ToolChain.cpp
    M clang/test/Driver/print-multi-selection-flags.c

  Log Message:
  -----------
  [Multilib] Add -fmultilib-flag command-line option (#110658)

This patch is the second step to extend the current multilib system to
support the selection of library variants which do not correspond to
existing command-line options.

Proposal can be found in
https://discourse.llvm.org/t/rfc-multilib-custom-flags/81058

The multilib mechanism supports libraries that target code generation or
language options such as --target, -mcpu, -mfpu, -mbranch-protection.
However, some library variants are particular to features that do not
correspond to any command-line options. Examples include variants for
multithreading and semihosting.

This work introduces a way to instruct the multilib system to consider
these features in library selection.

The driver must be informed about the multilib custom flags with a new
command-line option.
```
-fmultilib-flag=C
```
Where the grammar for C is:
```
C -> option
option -> multithreaded | no-multithreaded | io-none | io-semihosting | io-linux-syscalls | ...
```
There must be one option instance for each flag specified:
```
-fmultilib-flag=multithreaded -fmultilib-flag=io-semihosting
```
Contradictory options are untied by *last one wins*.

These options are to be used exclusively by the multilib mechanism in
the Clang driver. Hence they are not forwarded to the compiler frontend.



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