[RISCV] Specify MaxAtomicInlineWidth for RISC-V

[lewis-revill]

Summary

This prevents Clang from generating libcalls which are not necessary when the target has atomic support.

[asb]

Thanks Lewis, I actually had a patch for this which I forgot to clean up and submit. I've done so now: D57450. That adds tests, and sets MaxAtomicInlineWidth and MaxAtomicPromoteWidth conditionally based on whether the target has the atomics extension or not.

[lewis-revill]

Abandoned in favour of D57450

lib/Basic/Targets/RISCV.h

 };
 class LLVM_LIBRARY_VISIBILITY RISCV32TargetInfo : public RISCVTargetInfo {
 public:
   RISCV32TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : RISCVTargetInfo(Triple, Opts) {
     IntPtrType = SignedInt;
     PtrDiffType = SignedInt;
     SizeType = UnsignedInt;
+    MaxAtomicInlineWidth = 32;
     resetDataLayout("e-m:e-p:32:32-i64:64-n32-S128");
   }
 
   bool setABI(const std::string &Name) override {
     // TODO: support ilp32f and ilp32d ABIs.
     if (Name == "ilp32") {
       ABI = Name;
       return true;
     }
     return false;
   }
 };
 class LLVM_LIBRARY_VISIBILITY RISCV64TargetInfo : public RISCVTargetInfo {
 public:
   RISCV64TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : RISCVTargetInfo(Triple, Opts) {
     LongWidth = LongAlign = PointerWidth = PointerAlign = 64;
     IntMaxType = Int64Type = SignedLong;
+    MaxAtomicInlineWidth = 64;
     resetDataLayout("e-m:e-p:64:64-i64:64-i128:128-n64-S128");
   }
 
   bool setABI(const std::string &Name) override {
     // TODO: support lp64f and lp64d ABIs.
     if (Name == "lp64") {
       ABI = Name;
       return true;
     }
     return false;
   }
 };
 } // namespace targets
 } // namespace clang
 
 #endif // LLVM_CLANG_LIB_BASIC_TARGETS_RISCV_H