[llvm] [RISCV] Support Global Dynamic TLSDESC in the RISC-V backend (PR #66915)

[Craig Topper via llvm-commits]

================
@@ -3107,6 +3136,41 @@ void RISCVAsmParser::emitLoadTLSGDAddress(MCInst &Inst, SMLoc IDLoc,
                     RISCV::ADDI, IDLoc, Out);
 }
 
+void RISCVAsmParser::emitLoadTLSDescAddress(MCInst &Inst, SMLoc IDLoc,
+                                            MCStreamer &Out) {
+  // The load TLS GD address pseudo-instruction "la.tlsdesc" is used in
+  // global-dynamic TLS model addressing of global symbols:
+  //   la.tlsdesc rdest, symbol
+  // expands to
+  //   TmpLabel: AUIPC rdest, %tlsdesc_hi(symbol)
+  //             ADDI rdest, rdest, %pcrel_lo(TmpLabel)
+  MCOperand DestReg = Inst.getOperand(0);
+  const MCExpr *Symbol = Inst.getOperand(1).getExpr();
+
+  MCContext &Ctx = getContext();
+
+  MCSymbol *TmpLabel = Ctx.createNamedTempSymbol("pcrel_hi");
+  Out.emitLabel(TmpLabel);
+
+  const RISCVMCExpr *SymbolHi =
+      RISCVMCExpr::create(Symbol, RISCVMCExpr::VK_RISCV_TLSDESC_HI, Ctx);
+  emitToStreamer(
+      Out, MCInstBuilder(RISCV::AUIPC).addOperand(DestReg).addExpr(SymbolHi));
+
+  const MCExpr *RefToLinkTmpLabel =
+      RISCVMCExpr::create(MCSymbolRefExpr::create(TmpLabel, Ctx),
+                          RISCVMCExpr::VK_RISCV_TLSDESC_LOAD_LO, Ctx);
+
+  emitToStreamer(Out, MCInstBuilder(RISCV::ADDI)
+                          .addOperand(DestReg)
+                          .addOperand(DestReg)
+                          .addExpr(RefToLinkTmpLabel));
+
+  emitToStreamer(
+      Out,
+      MCInstBuilder(RISCV::JALR).addReg(RISCV::X5).addReg(RISCV::X5).addImm(0));
----------------
topperc wrote:

Should this use DestReg instead of X5?

https://github.com/llvm/llvm-project/pull/66915