[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, 1 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 4195bb8..e765bbf 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -470,6 +470,7 @@ static bool initTargetOptions(DiagnosticsEngine &Diags,
   Options.MCOptions.AsmVerbose = CodeGenOpts.AsmVerbose;
   Options.MCOptions.Dwarf64 = CodeGenOpts.Dwarf64;
   Options.MCOptions.PreserveAsmComments = CodeGenOpts.PreserveAsmComments;
+  Options.MCOptions.Crel = CodeGenOpts.Crel;
   Options.MCOptions.X86RelaxRelocations = CodeGenOpts.RelaxELFRelocations;
   Options.MCOptions.CompressDebugSections =
       CodeGenOpts.getCompressDebugSections();