[llvm] [CodeGen] Add MO_LaneMask type and a new COPY_LANEMASK instruction (PR #151944)

[Jay Foad via llvm-commits]

================
@@ -2428,6 +2428,46 @@ void MachineVerifier::visitMachineInstrBefore(const MachineInstr *MI) {
     }
     break;
   }
+  case TargetOpcode::COPY_LANEMASK: {
+    const MachineOperand &DstOp = MI->getOperand(0);
+    const MachineOperand &SrcOp = MI->getOperand(1);
+    const MachineOperand &LaneMaskOp = MI->getOperand(2);
+    const Register SrcReg = SrcOp.getReg();
+    const LaneBitmask LaneMask = LaneMaskOp.getLaneMask();
+    LaneBitmask SrcMaxLaneMask = LaneBitmask::getAll();
+
+    if (DstOp.getSubReg())
+      report("COPY_LANEMASK must not use a subregister index", &DstOp, 0);
+
+    if (SrcOp.getSubReg())
+      report("COPY_LANEMASK must not use a subregister index", &SrcOp, 1);
+
+    if (LaneMask.none())
+      report("COPY_LANEMASK must read at least one lane", MI);
+
+    if (SrcReg.isPhysical()) {
+      const TargetRegisterClass *SrcRC = TRI->getMinimalPhysRegClass(SrcReg);
+      if (SrcRC)
+        SrcMaxLaneMask = SrcRC->getLaneMask();
+    } else {
+      SrcMaxLaneMask = MRI->getMaxLaneMaskForVReg(SrcReg);
+    }
+
+    // COPY_LANEMASK should be used only for partial copy. For full
+    // copy, one should strictly use the COPY instruction.
+    if (SrcMaxLaneMask == LaneMask)
+      report("COPY_LANEMASK cannot be used to do full copy", MI);
+
+    // If LaneMask is equal to OR greater than the SrcMaxLaneMask, it
----------------
jayfoad wrote:

```suggestion
    // If LaneMask is greater than the SrcMaxLaneMask, it
```

https://github.com/llvm/llvm-project/pull/151944