[llvm] [MC][SystemZ] Introduce Target Specific HLASM Streamer for z/OS (PR #130535)

[via llvm-commits]

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@@ -34,12 +35,27 @@ void SystemZHLASMInstPrinter::printInst(const MCInst *MI, uint64_t Address,
   raw_string_ostream RSO(Str);
   printInstruction(MI, Address, RSO);
   // Eat the first tab character and replace it with a space since it is
-  // hardcoded in AsmWriterEmitter::EmitPrintInstruction
-  // TODO: introduce a line prefix member to AsmWriter to avoid this problem
+  // hardcoded in AsmWriterEmitter::EmitPrintInstruction.
+  // TODO Introduce a line prefix member to AsmWriter to avoid this problem.
   if (!Str.empty() && Str.front() == '\t')
     O << " " << Str.substr(1, Str.length());
   else
     O << Str;
 
   printAnnotation(O, Annot);
 }
+
+void SystemZHLASMInstPrinter::printPCRelOperand(const MCInst *MI, int OpNum,
+                                                raw_ostream &O) {
+  const MCOperand &MO = MI->getOperand(OpNum);
+  if (MO.isImm()) {
+    WithMarkup M = markup(O, Markup::Immediate);
+    O << "0x";
+    O.write_hex(MO.getImm());
+  } else {
+    // Don't print @PLT.
+    // TODO May need to do something more here.
+    const MCSymbolRefExpr &SRE = cast<MCSymbolRefExpr>(*(MO.getExpr()));
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tltao wrote:

Correct me if I'm wrong, but this looks to be the only way to access the `MCSymbol` referenced by a `MCExpr`. Looking at some AArch64/RISC-V examples from `AArch64MCExpr.cpp`/`RISCVMCExpr.cpp`, they are still forced to cast to `MCSymbolRefExpr` sometimes:
```
const MCSymbolRefExpr &SymRef = *cast<MCSymbolRefExpr>(Expr);
cast<MCSymbolELF>(SymRef.getSymbol()).setType(ELF::STT_TLS);
```
I'm not sure this is a case of using `MCSymbolRefExpr::VariantKind`? 

https://github.com/llvm/llvm-project/pull/130535