[llvm] [SPARC] Implement L and H inline asm argument modifiers (PR #87259)

[Jessica Clarke via llvm-commits]

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@@ -434,6 +434,50 @@ bool SparcAsmPrinter::PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
     default:
       // See if this is a generic print operand
       return AsmPrinter::PrintAsmOperand(MI, OpNo, ExtraCode, O);
+    case 'L': // Low order register of a twin word register operand
+    case 'H': // High order register of a twin word register operand
+    {
+      const SparcSubtarget &Subtarget = MF->getSubtarget<SparcSubtarget>();
+      const MachineOperand &MO = MI->getOperand(OpNo);
+      const SparcRegisterInfo *RegisterInfo = Subtarget.getRegisterInfo();
+      Register MOReg = MO.getReg();
+
+      Register HiReg, LoReg;
+      if (!SP::IntPairRegClass.contains(MOReg)) {
+        // If we aren't given a register pair already, find out which pair it
+        // belongs to. Note that here, the specified register operand, which
+        // refers to the high part of the twinword, needs to be an even-numbered
+        // register.
+        MOReg = RegisterInfo->getMatchingSuperReg(MOReg, SP::sub_even,
+                                                  &SP::IntPairRegClass);
+        if (!MOReg) {
+          SMLoc Loc;
+          OutContext.reportError(
+              Loc, "Hi part of pair should point to an even-numbered register");
+          OutContext.reportError(
+              Loc, "(note that in some cases it might be necessary to manually "
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jrtc27 wrote:

No, the fact that it can just fail arbitrarily rather than the compiler ensuring it's in the right register class

https://github.com/llvm/llvm-project/pull/87259