[RISC-V][GlobaISel] Legalize G_ATOMIC_CMPXCHG and G_ATOMIC_CMPXCHG_WITH_SUCCESS (#157634)

This change introduces legalization for `G_ATOMIC_CMPXCHG` and
`G_ATOMIC_CMPXCHG_WITH_SUCCESS`. Additionally, support for the
`riscv_masked_cmpxchg intrinsic` is added to legalizeIntrinsic, ensuring
that masked compare-and-exchange operations are recognized during
legalization.

---------

Co-authored-by: Kane Wang <[email protected]>

Author: ReVe1uv

llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp

@@ -702,7 +702,10 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
       .customIf(all(typeIsLegalIntOrFPVec(0, IntOrFPVecTys, ST),
                     typeIsLegalIntOrFPVec(1, IntOrFPVecTys, ST)));
 
-  getActionDefinitionsBuilder(G_ATOMICRMW_ADD)
+  getActionDefinitionsBuilder(G_ATOMIC_CMPXCHG_WITH_SUCCESS)
+      .lowerIf(all(typeInSet(0, {s8, s16, s32, s64}), typeIs(2, p0)));
+
+  getActionDefinitionsBuilder({G_ATOMIC_CMPXCHG, G_ATOMICRMW_ADD})
       .legalFor(ST.hasStdExtA(), {{sXLen, p0}})
       .libcallFor(!ST.hasStdExtA(), {{s8, p0}, {s16, p0}, {s32, p0}, {s64, p0}})
       .clampScalar(0, sXLen, sXLen);
@@ -751,6 +754,7 @@ bool RISCVLegalizerInfo::legalizeIntrinsic(LegalizerHelper &Helper,
   }
   case Intrinsic::riscv_masked_atomicrmw_add:
   case Intrinsic::riscv_masked_atomicrmw_sub:
+  case Intrinsic::riscv_masked_cmpxchg:
     return true;
   }
 }