[llvm-commits] CVS: llvm/lib/Transforms/Scalar/LoopSimplify.cpp

[Chris Lattner]

Changes in directory llvm/lib/Transforms/Scalar:

LoopSimplify.cpp updated: 1.44 -> 1.45

---
Log message:

Fix PR404: http://llvm.cs.uiuc.edu/PR404 : Loop simplify is really slow on 252.eon

This eliminates an N*N*logN algorithm from the loop simplify pass, replacing
it with a much simpler and faster alternative.  In a debug build, this reduces
gccas time on eon from 85s to 42s.



---
Diffs of the changes:  (+12 -12)

Index: llvm/lib/Transforms/Scalar/LoopSimplify.cpp
diff -u llvm/lib/Transforms/Scalar/LoopSimplify.cpp:1.44 llvm/lib/Transforms/Scalar/LoopSimplify.cpp:1.45
--- llvm/lib/Transforms/Scalar/LoopSimplify.cpp:1.44	Sun Apr 18 17:27:10 2004
+++ llvm/lib/Transforms/Scalar/LoopSimplify.cpp	Wed Jul 14 23:27:04 2004
@@ -147,6 +147,9 @@
     Changed = true;
   }
 
+
+  DominatorSet &DS = getAnalysis<DominatorSet>();  // Update dominator info
+
   // Next, check to make sure that all exit nodes of the loop only have
   // predecessors that are inside of the loop.  This check guarantees that the
   // loop preheader/header will dominate the exit blocks.  If the exit block has
@@ -155,19 +158,16 @@
   L->getExitBlocks(ExitBlocks);
   for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
     BasicBlock *ExitBlock = ExitBlocks[i];
-    for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
-         PI != PE; ++PI)
-      if (!L->contains(*PI)) {
-        BasicBlock *NewBB = RewriteLoopExitBlock(L, ExitBlock);
-        for (unsigned j = i; j != ExitBlocks.size(); ++j)
-          if (ExitBlocks[j] == ExitBlock)
-            ExitBlocks[j] = NewBB;
-
-        NumInserted++;
-        Changed = true;
-        break;
-      }
+    if (!DS.dominates(L->getHeader(), ExitBlock)) {
+      BasicBlock *NewBB = RewriteLoopExitBlock(L, ExitBlock);
+      for (unsigned j = i; j != ExitBlocks.size(); ++j)
+        if (ExitBlocks[j] == ExitBlock)
+          ExitBlocks[j] = NewBB;
+      
+      NumInserted++;
+      Changed = true;
     }
+  }
 
   // If the header has more than two predecessors at this point (from the
   // preheader and from multiple backedges), we must adjust the loop.