[Driver] Add -Wa, options --crel and --allow-experimental-crel

The two options are discussed in a few comments around
https://github.com/llvm/llvm-project/pull/91280#issuecomment-2099344079

* -Wa,--crel: error "-Wa,--allow-experimental-crel must be specified to use -Wa,--crel..."
* -Wa,--allow-experimental-crel: no-op
* -Wa,--crel,--allow-experimental-crel: enable CREL in the integrated assembler (#91280)

MIPS's little-endian n64 ABI messed up the `r_info` field in
relocations. While this could be fixed with CREL, my intention is to
avoid complication in assembler/linker. The implementation simply
doesn't allow CREL for MIPS.

Link: https://discourse.llvm.org/t/rfc-crel-a-compact-relocation-format-for-elf/77600

Pull Request: https://github.com/llvm/llvm-project/pull/97378

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/tools/driver/cc1as_main.cpp b/clang/tools/driver/cc1as_main.cpp
index ce1e181..4e0aa14 100644
--- a/clang/tools/driver/cc1as_main.cpp
+++ b/clang/tools/driver/cc1as_main.cpp
@@ -164,6 +164,9 @@ struct AssemblerInvocation {
   LLVM_PREFERRED_TYPE(bool)
   unsigned EmitCompactUnwindNonCanonical : 1;
 
+  LLVM_PREFERRED_TYPE(bool)
+  unsigned Crel : 1;
+
   /// The name of the relocation model to use.
   std::string RelocationModel;
 
@@ -204,6 +207,7 @@ public:
     EmbedBitcode = 0;
     EmitDwarfUnwind = EmitDwarfUnwindType::Default;
     EmitCompactUnwindNonCanonical = false;
+    Crel = false;
   }
 
   static bool CreateFromArgs(AssemblerInvocation &Res,
@@ -373,6 +377,7 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
 
   Opts.EmitCompactUnwindNonCanonical =
       Args.hasArg(OPT_femit_compact_unwind_non_canonical);
+  Opts.Crel = Args.hasArg(OPT_crel);
 
   Opts.AsSecureLogFile = Args.getLastArgValue(OPT_as_secure_log_file);
 
@@ -430,6 +435,7 @@ static bool ExecuteAssemblerImpl(AssemblerInvocation &Opts,
   MCOptions.EmitDwarfUnwind = Opts.EmitDwarfUnwind;
   MCOptions.EmitCompactUnwindNonCanonical = Opts.EmitCompactUnwindNonCanonical;
   MCOptions.MCSaveTempLabels = Opts.SaveTemporaryLabels;
+  MCOptions.Crel = Opts.Crel;
   MCOptions.X86RelaxRelocations = Opts.RelaxELFRelocations;
   MCOptions.CompressDebugSections = Opts.CompressDebugSections;
   MCOptions.AsSecureLogFile = Opts.AsSecureLogFile;