[llvm] [TableGen] Extend direct lookup to instruction values in generic tables. (PR #80486)

[Jason Eckhardt via llvm-commits]

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@@ -646,11 +671,23 @@ void SearchableTableEmitter::collectTableEntries(
     if (auto RecordTy = dyn_cast<RecordRecTy>(Field.RecType)) {
       if (IntrinsicClass && RecordTy->isSubClassOf(IntrinsicClass))
         Field.IsIntrinsic = true;
-      else if (InstructionClass && RecordTy->isSubClassOf(InstructionClass))
+      else if (InstructionClass && RecordTy->isSubClassOf(InstructionClass)) {
         Field.IsInstruction = true;
+        SawInstructionField = true;
+      }
     }
   }
 
+  // Build instruction-to-int map to check for contiguous instruction values.
+  // These are the same values emitted by InstrInfoEmitter. Do this on demand
+  // only after it is known that there are definitely instruction fields.
+  if (SawInstructionField && InstrEnumValueMap.empty()) {
+    CodeGenTarget Target(Records);
+    unsigned Num = 0;
+    for (const CodeGenInstruction *Inst : Target.getInstructionsByEnumValue())
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nvjle wrote:

As you suggested, I have moved this map into `CodeGenTarget::InstrToIntMap` and added a lookup method `CodeGenTarget::getInstrIntValue`. The map is now populated in `CodeGenTarget::computeInstrsByEnum` right after the sort that creates the order in the first place. 

Overall this is cleaner and simplified the patch as well. Thanks again for the suggestions.

In a follow-up patch, as you alluded to, I could use the new query in `InstrInfoEmitter::emitEnums` (and elsewhere if applicable) to reuse/sync the logic.

https://github.com/llvm/llvm-project/pull/80486