[PATCH] D49124: [Tablegen] Optimize isSubsetOf() in AsmMatcherEmitter.cpp

[Marcello Maggioni via Phabricator via llvm-commits]

kariddi created this revision.
kariddi added reviewers: dblaikie, craig.topper, ddunbar.
Herald added a subscriber: llvm-commits.

isSubsetOf() could be very slow if the hierarchy of the RegisterClasses of the target is very complicated.

This is mainly caused by the fact that isSubset() is called multiple times over the same SuperClass of a register class if this ends up being the super class of a register class from multiple paths.


Repository:
  rL LLVM

https://reviews.llvm.org/D49124

Files:
  utils/TableGen/AsmMatcherEmitter.cpp


Index: utils/TableGen/AsmMatcherEmitter.cpp
===================================================================
--- utils/TableGen/AsmMatcherEmitter.cpp
+++ utils/TableGen/AsmMatcherEmitter.cpp
@@ -272,10 +272,18 @@
     if (this == &RHS)
       return true;
 
+    SmallVector<const ClassInfo *, 16> Worklist(SuperClasses.begin(),
+                                                SuperClasses.end());
+    SmallPtrSet<const ClassInfo *, 16> Visited;
     // ... or if any of its super classes are a subset of RHS.
-    for (const ClassInfo *CI : SuperClasses)
-      if (CI->isSubsetOf(RHS))
+    while (!Worklist.empty()) {
+      auto *CI = Worklist.pop_back_val();
+      if (CI == &RHS)
         return true;
+      for (auto *Super : CI->SuperClasses)
+        if (Visited.insert(Super).second)
+          Worklist.push_back(Super);
+    }
 
     return false;
   }


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