[llvm] [ARM][TableGen][MC] Change the ARM mnemonic operands to be optional for ASM parsing (PR #83436)

[Ivan Kosarev via llvm-commits]

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@@ -608,12 +627,19 @@ struct MatchableInfo {
   void buildInstructionResultOperands();
   void buildAliasResultOperands(bool AliasConstraintsAreChecked);
 
-  /// operator< - Compare two matchables.
-  bool operator<(const MatchableInfo &RHS) const {
+  /// comp - Compare two matchables.
+  bool comp(const MatchableInfo &RHS, const CodeGenTarget &Target) const {
     // The primary comparator is the instruction mnemonic.
     if (int Cmp = Mnemonic.compare_insensitive(RHS.Mnemonic))
       return Cmp == -1;
 
+    // Sort by the resultant instuctions size, eg. for ARM instructions
+    // we must choose the smallest matching instruction.
+    if (Target.getSortBySize()) {
+      if (ResInstSize != RHS.ResInstSize)
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kosarev wrote:

Can be a single `if`. +Same below.

https://github.com/llvm/llvm-project/pull/83436