[RISCV] Move DebugLoc Copy into CompressInstEmitter

[lenary]

Summary

This copy ensures that debug location information is kept for
compressed instructions. There are places where both compressInstruction and
uncompressInstruction are called that were not doing this copy, discarding some
debug info.

This change merely moves the copy into the generated file, so you cannot forget
to copy the location over when compressing or uncompressing.

[lenary]

• Update Location Copy Code

[luismarques]

You could add a test that shows the change; no debug loc before, and debug loc after the patch.

[lenary]

Rebased and added a test to ensure debug info is preserved.

The test doesn't actually fail without this patch, but this ensures it won't
fail in future.

[luismarques]

LGTM

llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

Warning(Parser.getTok().getLoc(),
           "'norelax'");
   Parser.eatToEndOfStatement();
   return false;
 }
 
 void RISCVAsmParser::emitToStreamer(MCStreamer &S, const MCInst &Inst) {
   MCInst CInst;
   bool Res = compressInst(CInst, Inst, getSTI(), S.getContext());
-  CInst.setLoc(Inst.getLoc());
   S.EmitInstruction((Res ? CInst : Inst), getSTI());
 }
 
 void RISCVAsmParser::emitLoadImm(Register DestReg, int64_t Value,
                                  MCStreamer &Out) {
   RISCVMatInt::InstSeq Seq;
   RISCVMatInt::generateInstSeq(Value, isRV64(), Seq);
 

llvm/test/MC/RISCV/compress-debug-info.s

+# RUN: llvm-mc -triple riscv32 -mattr=+c %s -g -o - -riscv-no-aliases \
+# RUN:   | FileCheck %s -check-prefixes=COMPRESS,BOTH
+# RUN: llvm-mc -triple riscv32 %s -g -o - -riscv-no-aliases \
+# RUN:   | FileCheck %s -check-prefixes=UNCOMPRESS,BOTH
+
+
+# This file ensures that compressing an instruction preserves its debug info.
+
+
+# BOTH-LABEL: .text
+
+# BOTH: .file 1
+# BOTH-SAME: "compress-debug-info.s"
+
+# BOTH:            .loc 1 [[# @LINE + 3 ]] 0
+# UNCOMPRESS-NEXT: addi a0, a1, 0
+# COMPRESS-NEXT:   c.mv a0, a1
+addi a0, a1, 0
+
+# BOTH-LABEL: .debug_info

llvm/utils/TableGen/RISCVCompressInstEmitter.cpp

for (const auto &DestOperand : Dest.Operands) {
         Record *Reg = DestOperandMap[OpNo].Data.Reg;
         CodeStream.indent(6) << "OutInst.addOperand(MCOperand::createReg(" +
                                     Namespace + "::" + Reg->getName().str() +
                                     "));\n";
       } break;
       }
       ++OpNo;
     }
+    CodeStream.indent(6) << "OutInst.setLoc(MI.getLoc());\n";
     CaseStream << mergeCondAndCode(CondStream, CodeStream);
     PrevOp = CurOp;
   }
   Func << CaseStream.str() << "\n";
   // Close brace for the last case.
   Func.indent(4) << "} // case " + CurOp + "\n";
   Func.indent(2) << "} // switch\n";
   Func.indent(2) << "return false;\n}\n";