[clang][Driver] Support passing arbitrary args to -cc1as with -Xclangas.

Closes #97517.

Author: alexrp

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
 ^^^^^^^^^^^^^^^^^^

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">,

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())

clang/test/Driver/Xclangas.s

@@ -0,0 +1,6 @@
+// Check that -Xclangas passes args to -cc1as.
+// RUN: %clang -### -Xclangas -target-feature -Xclangas +v5t %s 2>&1 | \
+// RUN:   FileCheck -check-prefix=ARGS %s
+// ARGS: -cc1as
+// ARGS: -target-feature
+// ARGS: +v5t