[LoongArch][NFC] Fix the operand constraint of AMCAS instructions

The `rd` operand of AMCAS instructions is both read and written, because
of the nature of compare-and-swap operations, but currently it is not
declared as such. Fix it for upcoming codegen enablement changes. In
order to do that, a piece of LoongArchAsmParser logic that relied on
TableGen-erated enum variants being ordered in a specific way needs
updating; this will be addressed in a following refactor. No functional
change intended.

While at it, restore vertical alignment for the definition lines.

Suggested-by: tangaac <[email protected]>
Link: #114398 (comment)

Author: xen0n

llvm/lib/Target/LoongArch/AsmParser/LoongArchAsmParser.cpp

@@ -1562,7 +1562,13 @@ unsigned LoongArchAsmParser::checkTargetMatchPredicate(MCInst &Inst) {
   unsigned Opc = Inst.getOpcode();
   switch (Opc) {
   default:
-    if (Opc >= LoongArch::AMADD_D && Opc <= LoongArch::AMXOR_W) {
+    if (Opc >= LoongArch::AMCAS_B && Opc <= LoongArch::AMCAS__DB_W) {
+      MCRegister Rd = Inst.getOperand(0).getReg();
+      MCRegister Rk = Inst.getOperand(2).getReg();
+      MCRegister Rj = Inst.getOperand(3).getReg();
+      if ((Rd == Rk || Rd == Rj) && Rd != LoongArch::R0)
+        return Match_RequiresAMORdDifferRkRj;
+    } else if (Opc >= LoongArch::AMADD_D && Opc <= LoongArch::AMXOR_W) {
       MCRegister Rd = Inst.getOperand(0).getReg();
       MCRegister Rk = Inst.getOperand(1).getReg();
       MCRegister Rj = Inst.getOperand(2).getReg();

llvm/lib/Target/LoongArch/LoongArchInstrInfo.td

@@ -715,6 +715,11 @@ class AM_3R<bits<32> op>
     : Fmt3R<op, (outs GPR:$rd), (ins GPR:$rk, GPRMemAtomic:$rj),
             "$rd, $rk, $rj">;
 
+let hasSideEffects = 0, mayLoad = 1, mayStore = 1, Constraints = "$rd = $rd_wb" in
+class AMCAS_3R<bits<32> op>
+    : Fmt3R<op, (outs GPR:$rd_wb), (ins GPR:$rd, GPR:$rk, GPRMemAtomic:$rj),
+            "$rd, $rk, $rj">;
+
 let hasSideEffects = 0, mayLoad = 1, mayStore = 0 in {
 class LLBase<bits<32> op>
     : Fmt2RI14<op, (outs GPR:$rd), (ins GPR:$rj, simm14_lsl2:$imm14),
@@ -1024,14 +1029,14 @@ def AMMAX__DB_WU : AM_3R<0x38700000>;
 def AMMAX__DB_DU : AM_3R<0x38708000>;
 def AMMIN__DB_WU : AM_3R<0x38710000>;
 def AMMIN__DB_DU : AM_3R<0x38718000>;
-def AMCAS_B     : AM_3R<0x38580000>;
-def AMCAS_H     : AM_3R<0x38588000>;
-def AMCAS_W     : AM_3R<0x38590000>;
-def AMCAS_D     : AM_3R<0x38598000>;
-def AMCAS__DB_B     : AM_3R<0x385a0000>;
-def AMCAS__DB_H     : AM_3R<0x385a8000>;
-def AMCAS__DB_W     : AM_3R<0x385b0000>;
-def AMCAS__DB_D     : AM_3R<0x385b8000>;
+def AMCAS_B      : AMCAS_3R<0x38580000>;
+def AMCAS_H      : AMCAS_3R<0x38588000>;
+def AMCAS_W      : AMCAS_3R<0x38590000>;
+def AMCAS_D      : AMCAS_3R<0x38598000>;
+def AMCAS__DB_B  : AMCAS_3R<0x385a0000>;
+def AMCAS__DB_H  : AMCAS_3R<0x385a8000>;
+def AMCAS__DB_W  : AMCAS_3R<0x385b0000>;
+def AMCAS__DB_D  : AMCAS_3R<0x385b8000>;
 def LL_D : LLBase<0x22000000>;
 def SC_D : SCBase<0x23000000>;
 def SC_Q : SCBase_128<0x38570000>;