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

[Jay Foad via llvm-commits]

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@@ -2873,6 +2876,32 @@ bool MIParser::parseCustomRegisterMaskOperand(MachineOperand &Dest) {
   return false;
 }
 
+bool MIParser::parseLaneMaskOperand(MachineOperand &Dest) {
+  assert(Token.is(MIToken::kw_lanemask));
+
+  lex();
+  if (expectAndConsume(MIToken::lparen))
+    return true;
+
+  LaneBitmask LaneMask = LaneBitmask::getAll();
+  // Parse lanemask.
+  if (Token.isNot(MIToken::IntegerLiteral) && Token.isNot(MIToken::HexLiteral))
+    return error("expected a valid lane mask value");
+  static_assert(sizeof(LaneBitmask::Type) == sizeof(uint64_t),
+                "Use correct get-function for lane mask.");
+  LaneBitmask::Type V;
+  if (getUint64(V))
+    return true;
+  LaneMask = LaneBitmask(V);
----------------
jayfoad wrote:

No need for the earlier declaration, you can just initialize it here.
```suggestion
  LaneBitmask LaneMask(V);
```

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