[llvm] r337020 - [Tablegen] Optimize isSubsetOf() in AsmMatcherEmitter.cpp. NFC

[Marcello Maggioni via llvm-commits]

Author: mggm
Date: Fri Jul 13 09:36:14 2018
New Revision: 337020

URL: http://llvm.org/viewvc/llvm-project?rev=337020&view=rev
Log:
[Tablegen] Optimize isSubsetOf() in AsmMatcherEmitter.cpp. NFC

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.

Differential Revision: https://reviews.llvm.org/D49124

Modified:
    llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp

Modified: llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp?rev=337020&r1=337019&r2=337020&view=diff
==============================================================================
--- llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp (original)
+++ llvm/trunk/utils/TableGen/AsmMatcherEmitter.cpp Fri Jul 13 09:36:14 2018
@@ -273,9 +273,17 @@ public:
       return true;
 
     // ... or if any of its super classes are a subset of RHS.
-    for (const ClassInfo *CI : SuperClasses)
-      if (CI->isSubsetOf(RHS))
+    SmallVector<const ClassInfo *, 16> Worklist(SuperClasses.begin(),
+                                                SuperClasses.end());
+    SmallPtrSet<const ClassInfo *, 16> Visited;
+    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;
   }