[llvm-commits] [127543] From TOT: prevent exponential recursion in isNegatibleForFree

[bwendlin at apple.com]

Revision: 127543
Author:   bwendlin
Date:     2007-05-23 01:01:23 -0700 (Wed, 23 May 2007)

Log Message:
-----------
>From TOT: prevent exponential recursion in isNegatibleForFree

Modified Paths:
--------------
    apple-local/branches/llvm-leopard/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: apple-local/branches/llvm-leopard/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- apple-local/branches/llvm-leopard/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp	2007-05-23 07:02:15 UTC (rev 127542)
+++ apple-local/branches/llvm-leopard/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp	2007-05-23 08:01:23 UTC (rev 127543)
@@ -351,7 +351,10 @@
 /// isNegatibleForFree - Return 1 if we can compute the negated form of the
 /// specified expression for the same cost as the expression itself, or 2 if we
 /// can compute the negated form more cheaply than the expression itself.
-static char isNegatibleForFree(SDOperand Op) {
+static char isNegatibleForFree(SDOperand Op, unsigned Depth = 0) {
+  // Don't recurse exponentially.
+  if (Depth > 6) return false;
+  
   // fneg is removable even if it has multiple uses.
   if (Op.getOpcode() == ISD::FNEG) return 2;
   
@@ -367,10 +370,10 @@
     if (!UnsafeFPMath) return 0;
     
     // -(A+B) -> -A - B
-    if (char V = isNegatibleForFree(Op.getOperand(0)))
+    if (char V = isNegatibleForFree(Op.getOperand(0), Depth+1))
       return V;
     // -(A+B) -> -B - A
-    return isNegatibleForFree(Op.getOperand(1));
+    return isNegatibleForFree(Op.getOperand(1), Depth+1);
   case ISD::FSUB:
     // We can't turn -(A-B) into B-A when we honor signed zeros. 
     if (!UnsafeFPMath) return 0;
@@ -383,15 +386,15 @@
     if (HonorSignDependentRoundingFPMath()) return 0;
     
     // -(X*Y) -> (-X * Y) or (X*-Y)
-    if (char V = isNegatibleForFree(Op.getOperand(0)))
+    if (char V = isNegatibleForFree(Op.getOperand(0), Depth+1))
       return V;
       
-    return isNegatibleForFree(Op.getOperand(1));
+    return isNegatibleForFree(Op.getOperand(1), Depth+1);
     
   case ISD::FP_EXTEND:
   case ISD::FP_ROUND:
   case ISD::FSIN:
-    return isNegatibleForFree(Op.getOperand(0));
+    return isNegatibleForFree(Op.getOperand(0), Depth+1);
   }
 }