[llvm] [PowerPC] Add a set of extended mnemonics that are missing from Power 10. (PR #73003)

[Amy Kwan via llvm-commits]

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@@ -3437,6 +3437,23 @@ def crnot : OutPatFrag<(ops node:$in),
 def       : Pat<(not i1:$in),
                 (crnot $in)>;
 
+// Pseudo-instructions for alternate assembly syntax (never used by codegen).
+// These are aliases that require C++ handling to convert to the target
+// instruction, while InstAliases can be handled directly by tblgen.
+class PPCAsmPseudo<string asm, dag iops>
+  : Instruction {
+  let Namespace = "PPC";
+  bit PPC64 = 0;  // Default value, override with isPPC64
+
+  let OutOperandList = (outs);
+  let InOperandList = iops;
+  let Pattern = [];
+  let AsmString = asm;
+  let isAsmParserOnly = 1;
+  let isPseudo = 1;
+  let hasNoSchedulingInfo = 1;
+}
+
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amy-kwan wrote:

Is it because we need access to stuff like `isAsmParserOnly` and `hasNoSchedulingInfo` inside `PPCInstrP10.td`, as well?

https://github.com/llvm/llvm-project/pull/73003