[llvm-commits] [llvm] r83790 - /llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

[Chris Lattner]

Author: lattner
Date: Sun Oct 11 16:04:37 2009
New Revision: 83790

URL: http://llvm.org/viewvc/llvm-project?rev=83790&view=rev
Log:
populate instcombine's initial worklist more carefully, causing
it to visit instructions from the start of the function to the
end of the function in the first path.  This greatly speeds up
some pathological cases (e.g. PR5150). 

Modified:
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=83790&r1=83789&r2=83790&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Sun Oct 11 16:04:37 2009
@@ -12681,6 +12681,9 @@
                                        const TargetData *TD) {
   SmallVector<BasicBlock*, 256> Worklist;
   Worklist.push_back(BB);
+  
+  std::vector<Instruction*> InstrsForInstCombineWorklist;
+  InstrsForInstCombineWorklist.reserve(128);
 
   while (!Worklist.empty()) {
     BB = Worklist.back();
@@ -12727,7 +12730,7 @@
         DBI_Prev = 0;
       }
 
-      IC.Worklist.Add(Inst);
+      InstrsForInstCombineWorklist.push_back(Inst);
     }
 
     // Recursively visit successors.  If this is a branch or switch on a
@@ -12759,6 +12762,16 @@
     for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
       Worklist.push_back(TI->getSuccessor(i));
   }
+  
+  // Once we've found all of the instructions to add to instcombine's worklist,
+  // add them in reverse order.  This way instcombine will visit from the top
+  // of the function down.  This jives well with the way that it adds all uses
+  // of instructions to the worklist after doing a transformation, thus avoiding
+  // some N^2 behavior in pathological cases.
+  for (std::vector<Instruction*>::reverse_iterator
+       I = InstrsForInstCombineWorklist.rbegin(),
+       E = InstrsForInstCombineWorklist.rend(); I != E; ++I)
+    IC.Worklist.Add(*I);
 }
 
 bool InstCombiner::DoOneIteration(Function &F, unsigned Iteration) {