[llvm-commits] [llvm] r100285 - /llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp

[Chris Lattner]

Author: lattner
Date: Sat Apr  3 02:21:39 2010
New Revision: 100285

URL: http://llvm.org/viewvc/llvm-project?rev=100285&view=rev
Log:
require that the branch being controlled by the IV 
exits the loop.  With this information we can guarantee 
the iteration count of the loop is bounded by the 
compare.  I think this xforms is finally safe now.

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

Modified: llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp?rev=100285&r1=100284&r2=100285&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/IndVarSimplify.cpp Sat Apr  3 02:21:39 2010
@@ -691,8 +691,15 @@
   
   BranchInst *TheBr = cast<BranchInst>(Compare->use_back());
 
-  // FIXME: Need to verify that the branch actually controls the iteration count
-  // of the loop.  If not, the new IV can overflow and noone will notice.
+  // We need to verify that the branch actually controls the iteration count
+  // of the loop.  If not, the new IV can overflow and no one will notice.
+  // The branch block must be in the loop and one of the successors must be out
+  // of the loop.
+  assert(TheBr->isConditional() && "Can't use fcmp if not conditional");
+  if (!L->contains(TheBr->getParent()) ||
+      (L->contains(TheBr->getSuccessor(0)) &&
+       L->contains(TheBr->getSuccessor(1))))
+    return;
   
   
   // If it isn't a comparison with an integer-as-fp (the exit value), we can't