When performing return slot optimization, remember to inform memdep when we're removi...

[oota-llvm.git] / lib / Transforms / Scalar / TailRecursionElimination.cpp

diff --git a/lib/Transforms/Scalar/TailRecursionElimination.cpp b/lib/Transforms/Scalar/TailRecursionElimination.cpp
index c75b93015ca3f914e9028b3e2430b72dcc8f3309..5849254374d2ec39ed14bfeea7693d534c5eda2f 100644 (file)
--- a/lib/Transforms/Scalar/TailRecursionElimination.cpp
+++ b/lib/Transforms/Scalar/TailRecursionElimination.cpp
@@ -2,8 +2,8 @@
 //
 //                     The LLVM Compiler Infrastructure
 //
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
@@ -67,7 +67,7 @@ STATISTIC(NumAccumAdded, "Number of accumulators introduced");
 
 namespace {
   struct VISIBILITY_HIDDEN TailCallElim : public FunctionPass {
-    static const int ID; // Pass identifcation, replacement for typeid
+    static char ID; // Pass identification, replacement for typeid
     TailCallElim() : FunctionPass((intptr_t)&ID) {}
 
     virtual bool runOnFunction(Function &F);
@@ -80,7 +80,7 @@ namespace {
     bool CanMoveAboveCall(Instruction *I, CallInst *CI);
     Value *CanTransformAccumulatorRecursion(Instruction *I, CallInst *CI);
   };
-  const int TailCallElim::ID = 0;
+  char TailCallElim::ID = 0;
   RegisterPass<TailCallElim> X("tailcallelim", "Tail Call Elimination");
 }
 
@@ -302,6 +302,15 @@ bool TailCallElim::ProcessReturningBlock(ReturnInst *Ret, BasicBlock *&OldEntry,
 
   if (&BB->front() == Ret) // Make sure there is something before the ret...
     return false;
+  
+  // If the return is in the entry block, then making this transformation would
+  // turn infinite recursion into an infinite loop.  This transformation is ok
+  // in theory, but breaks some code like:
+  //   double fabs(double f) { return __builtin_fabs(f); } // a 'fabs' call
+  // disable this xform in this case, because the code generator will lower the
+  // call to fabs into inline code.
+  if (BB == &F->getEntryBlock())
+    return false;
 
   // Scan backwards from the return, checking to see if there is a tail call in
   // this block.  If so, set CI to it.