[clang] [llvm] [AMDGPU][WIP] Extend readlane, writelane and readfirstlane intrinsic lowering for generic types (PR #89217)

[Matt Arsenault via cfe-commits]

================
@@ -5387,6 +5387,212 @@ bool 
AMDGPULegalizerInfo::legalizeDSAtomicFPIntrinsic(LegalizerHelper &Helper,
   return true;
 }
 
+bool AMDGPULegalizerInfo::legalizeLaneOp(LegalizerHelper &Helper,
+                                         MachineInstr &MI,
+                                         Intrinsic::ID IID) const {
+
+  MachineIRBuilder &B = Helper.MIRBuilder;
+  MachineRegisterInfo &MRI = *B.getMRI();
+
+  Register DstReg = MI.getOperand(0).getReg();
+  Register Src0 = MI.getOperand(2).getReg();
+
+  auto createLaneOp = [&](Register Src0, Register Src1,
+                          Register Src2) -> Register {
+    auto LaneOp = B.buildIntrinsic(IID, {S32}).addUse(Src0);
+    switch (IID) {
+    case Intrinsic::amdgcn_readfirstlane:
+      return LaneOp.getReg(0);
+    case Intrinsic::amdgcn_readlane:
+      return LaneOp.addUse(Src1).getReg(0);
+    case Intrinsic::amdgcn_writelane:
+      return LaneOp.addUse(Src1).addUse(Src2).getReg(0);
+    default:
+      llvm_unreachable("unhandled lane op");
+    }
+  };
+
+  Register Src1, Src2;
+  if (IID == Intrinsic::amdgcn_readlane || IID == Intrinsic::amdgcn_writelane) 
{
+    Src1 = MI.getOperand(3).getReg();
+    if (IID == Intrinsic::amdgcn_writelane) {
+      Src2 = MI.getOperand(4).getReg();
+    }
+  }
+
+  LLT Ty = MRI.getType(DstReg);
+  unsigned Size = Ty.getSizeInBits();
+
+  if (Size == 32) {
+    if (Ty.isScalar())
+      // Already legal
+      return true;
+
+    auto IsPtr = Ty.isPointer();
+    Src0 = IsPtr ? B.buildPtrToInt(S32, Src0).getReg(0)
+                 : B.buildBitcast(S32, Src0).getReg(0);
----------------
arsenm wrote:

You should not need these casts. Any legal type should be directly accepted 
without these 

https://github.com/llvm/llvm-project/pull/89217
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