[llvm] r339890 - [TableGen] TypeSetByHwMode::operator== optimization

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Thu Aug 16 09:16:28 2018
New Revision: 339890

URL: http://llvm.org/viewvc/llvm-project?rev=339890&view=rev
Log:
[TableGen] TypeSetByHwMode::operator== optimization

This operator is called a great deal, by checking for the cheap isSimple equality cases first (a common occurrence) we can improve performance as we avoid a lot of std::map find/iteration in hasDefault.

isSimple also means that a default value is present, so we can avoid some hasDefault calls.

This also avoids a rather dodgy piece of logic that was checking for isSimple() && !VTS.isSimple() but not the inverse - it now uses the general hasDefault mode comparison test instead.

Saves around 15secs in debug builds of x86 -gen-dag-isel.

Differential Revision: https://reviews.llvm.org/D50841

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

Modified: llvm/trunk/utils/TableGen/CodeGenDAGPatterns.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/TableGen/CodeGenDAGPatterns.cpp?rev=339890&r1=339889&r2=339890&view=diff
==============================================================================
--- llvm/trunk/utils/TableGen/CodeGenDAGPatterns.cpp (original)
+++ llvm/trunk/utils/TableGen/CodeGenDAGPatterns.cpp Thu Aug 16 09:16:28 2018
@@ -198,15 +198,17 @@ void TypeSetByHwMode::writeToStream(cons
 }
 
 bool TypeSetByHwMode::operator==(const TypeSetByHwMode &VTS) const {
-  bool HaveDefault = hasDefault();
-  if (HaveDefault != VTS.hasDefault())
-    return false;
+  // The isSimple call is much quicker than hasDefault - check this first.
+  bool IsSimple = isSimple();
+  bool VTSIsSimple = VTS.isSimple();
+  if (IsSimple && VTSIsSimple)
+    return *begin() == *VTS.begin();
 
-  if (isSimple()) {
-    if (VTS.isSimple())
-      return *begin() == *VTS.begin();
+  // Speedup: We have a default if the set is simple.
+  bool HaveDefault = IsSimple || hasDefault();
+  bool VTSHaveDefault = VTSIsSimple || VTS.hasDefault();
+  if (HaveDefault != VTSHaveDefault)
     return false;
-  }
 
   SmallDenseSet<unsigned, 4> Modes;
   for (auto &I : *this)