[llvm] [TableGen] New tblgen Pattern bit to disable DAGISel pattern imports (PR #88382)

[Pierre van Houtryve via llvm-commits]

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@@ -1901,7 +1901,12 @@ std::optional<CodeGenSubRegIndex *> GlobalISelEmitter::inferSubRegIndexForNode(
   return CGRegs.getSubRegIdx(SubRegInit->getDef());
 }
 
-Expected<RuleMatcher> GlobalISelEmitter::runOnPattern(const PatternToMatch &P) {
+std::optional<Expected<RuleMatcher>>
+GlobalISelEmitter::runOnPattern(const PatternToMatch &P) {
+  if (P.getISelShouldIgnore()) {
+    return {};
+  }
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Pierre-vh wrote:

You can just check this in `run` before calling `runOnPattern`, then you don't need to change `runOnPattern` signature at all.

https://github.com/llvm/llvm-project/pull/88382