[clang] [clang][Driver] Support passing arbitrary args to -cc1as with -Xclangas. (PR #100714)

[Alex Rønne Petersen via cfe-commits]

https://github.com/alexrp created https://github.com/llvm/llvm-project/pull/100714

This is one of the ideas I gave in #97517. I opted to propose this one first as introducing a new `-Xclangas` option comes with no concerns about GCC compatibility as with `-Xassembler`.

I am not sure where would be an appropriate place to test this, or how it would make sense to do so. I would appreciate any guidance on this. I tested manually like this:

```console
❯ ./bin/clang -target arm-linux-gnueabi -c test.s
test.s:1:1: error: instruction requires: armv5t
blx lr
^
❯ make -j
❯ ./bin/clang -target arm-linux-gnueabi -c test.s -Xclangas -target-feature -Xclangas +v5t
❯ file test.o
test.o: ELF 32-bit LSB relocatable, ARM, EABI5 version 1 (SYSV), not stripped
```

>From c1da400d71a9b479e012362cb581b5fd7c95bfbe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex at alexrp.com>
Date: Fri, 26 Jul 2024 09:40:42 +0200
Subject: [PATCH] [clang][Driver] Support passing arbitrary args to -cc1as with
 -Xclangas.

Closes #97517.
---
 clang/docs/UsersManual.rst            | 1 +
 clang/include/clang/Driver/Options.td | 8 ++++++++
 clang/lib/Driver/ToolChains/Clang.cpp | 6 ++++++
 3 files changed, 15 insertions(+)

diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index e9b95739ea2ab..7f55080321fea 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -4876,6 +4876,7 @@ Execute ``clang-cl /?`` to see a list of supported options:
       -v                      Show commands to run and use verbose output
       -W<warning>             Enable the specified warning
       -Xclang <arg>           Pass <arg> to the clang compiler
+      -Xclangas <arg>         Pass <arg> to the clang assembler
 
 The /clang: Option
 ^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 26811bf948ae5..c7839c3941eb9 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1028,10 +1028,18 @@ def Xclang : Separate<["-"], "Xclang">,
   HelpText<"Pass <arg> to clang -cc1">, MetaVarName<"<arg>">,
   Flags<[NoXarchOption]>, Visibility<[ClangOption, CLOption, DXCOption]>,
   Group<CompileOnly_Group>;
+def Xclangas : Separate<["-"], "Xclangas">,
+  HelpText<"Pass <arg> to clang -cc1as">, MetaVarName<"<arg>">,
+  Flags<[NoXarchOption]>, Visibility<[ClangOption, CLOption, DXCOption]>,
+  Group<CompileOnly_Group>;
 def : Joined<["-"], "Xclang=">, Group<CompileOnly_Group>,
   Flags<[NoXarchOption]>, Visibility<[ClangOption, CLOption, DXCOption]>,
   Alias<Xclang>,
   HelpText<"Alias for -Xclang">, MetaVarName<"<arg>">;
+def : Joined<["-"], "Xclangas=">, Group<CompileOnly_Group>,
+  Flags<[NoXarchOption]>, Visibility<[ClangOption, CLOption, DXCOption]>,
+  Alias<Xclangas>,
+  HelpText<"Alias for -Xclangas">, MetaVarName<"<arg>">;
 def Xcuda_fatbinary : Separate<["-"], "Xcuda-fatbinary">,
   HelpText<"Pass <arg> to fatbinary invocation">, MetaVarName<"<arg>">;
 def Xcuda_ptxas : Separate<["-"], "Xcuda-ptxas">,
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 4a94df7d5f42e..90b8db11c46c6 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -8711,6 +8711,12 @@ void ClangAs::ConstructJob(Compilation &C, const JobAction &JA,
   CollectArgsForIntegratedAssembler(C, Args, CmdArgs,
                                     getToolChain().getDriver());
 
+  // Forward -Xclangas arguments to -cc1as
+  for (auto Arg : Args.filtered(options::OPT_Xclangas)) {
+    Arg->claim();
+    CmdArgs.push_back(Arg->getValue());
+  }
+
   Args.AddAllArgs(CmdArgs, options::OPT_mllvm);
 
   if (DebugInfoKind > llvm::codegenoptions::NoDebugInfo && Output.isFilename())