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

[Paul Kirth via llvm-commits]

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@@ -539,6 +545,53 @@ bool RISCVPreRAExpandPseudo::expandLoadTLSGDAddress(
                              RISCV::ADDI);
 }
 
+bool RISCVPreRAExpandPseudo::expandLoadTLSDescAddress(
+    MachineBasicBlock &MBB, MachineBasicBlock::iterator MBBI,
+    MachineBasicBlock::iterator &NextMBBI) {
+  MachineFunction *MF = MBB.getParent();
+  MachineInstr &MI = *MBBI;
+  DebugLoc DL = MI.getDebugLoc();
+
+  const auto &STI = MF->getSubtarget<RISCVSubtarget>();
+  unsigned SecondOpcode = STI.is64Bit() ? RISCV::LD : RISCV::LW;
+
+  Register FinalReg = MI.getOperand(0).getReg();
+  Register DestReg =
+      MF->getRegInfo().createVirtualRegister(&RISCV::GPRRegClass);
+  Register ScratchReg =
+      MF->getRegInfo().createVirtualRegister(&RISCV::GPRRegClass);
+
+  MachineOperand &Symbol = MI.getOperand(1);
+  Symbol.setTargetFlags(RISCVII::MO_TLSDESC_HI);
+  MCSymbol *AUIPCSymbol = MF->getContext().createNamedTempSymbol("tlsdesc_hi");
+
+  MachineInstr *MIAUIPC =
+      BuildMI(MBB, MBBI, DL, TII->get(RISCV::AUIPC), ScratchReg).add(Symbol);
+  MIAUIPC->setPreInstrSymbol(*MF, AUIPCSymbol);
+
+  BuildMI(MBB, MBBI, DL, TII->get(SecondOpcode), DestReg)
+      .addReg(ScratchReg)
+      .addSym(AUIPCSymbol, RISCVII::MO_TLSDESC_LOAD_LO);
+
+  BuildMI(MBB, MBBI, DL, TII->get(RISCV::ADDI), RISCV::X10)
+      .addReg(ScratchReg)
+      .addSym(AUIPCSymbol, RISCVII::MO_TLSDESC_ADD_LO);
+
+  BuildMI(MBB, MBBI, DL, TII->get(RISCV::PseudoTLSDESCCall), RISCV::X5)
+      .addReg(DestReg)
+      .addImm(0)
+      .addSym(AUIPCSymbol, RISCVII::MO_TLSDESC_CALL);
+
+  MachineInstr *TPAdd = BuildMI(MBB, MBBI, DL, TII->get(RISCV::ADD), FinalReg)
+                            .addReg(RISCV::X10)
+                            .addReg(RISCV::X4);
+
+  if (MI.hasOneMemOperand())
+    TPAdd->addMemOperand(*MF, *MI.memoperands_begin());
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ilovepi wrote:

That's a good point.  I'll update the patch to reflect that.

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