[CSKY] AsmBackend: Make Inst.dump() debug-only

[kees]

Summary

Production builds of CSKY will fail to link with an bare call to
Inst.dump(), which was introduced in commit 582836faafcb:

ld.lld: error: undefined symbol: llvm::MCInst::dump() const

referenced by CSKYAsmBackend.cpp

/home/kees/src/built-compilers/llvm/stage2-prof-gen/lto.cache/llvmcache-0656FC38C728A7FE0F767D10CD84C7F820114C46:(llvm::CSKYAsmBackend::relaxInstruction(llvm::MCInst&, llvm::MCSubtargetInfo const&) const)

Wrap it in LLVM_DEBUG().

Fixes https://github.com/llvm/llvm-project/issues/54684

[MaskRay]

s/production /-DLLVM_ENABLE_ASSERTIONS=OFF /

[zixuan-wu]

Is CSKY target enabled as default in lld building even it's an experimental target?

[MaskRay]

In D122854#3420995, @zixuan-wu wrote:

Is CSKY target enabled as default in lld building even it's an experimental target?

lld is irrelevant here. The gist here is that in -DLLVM_ENABLE_ASSERTIONS=OFF builds MCInst::dump is not defined. Any linker will report an error.

The description may not convey the idea clearly. I updated the commit message.

llvm/lib/Target/CSKY/MCTargetDesc/CSKYAsmBackend.cpp

 }
 
 void CSKYAsmBackend::relaxInstruction(MCInst &Inst,
                                       const MCSubtargetInfo &STI) const {
   MCInst Res;
 
   switch (Inst.getOpcode()) {
   default:
-    Inst.dump();
+    LLVM_DEBUG(Inst.dump());
     llvm_unreachable("Opcode not expected!");
   case CSKY::LRW16:
     Res.setOpcode(CSKY::LRW32);
     Res.addOperand(Inst.getOperand(0));
     Res.addOperand(Inst.getOperand(1));
     break;
   case CSKY::BR16:
     Res.setOpcode(CSKY::BR32);