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prevent exponential recursion in isNegatibleForFree

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llvm-svn: 37310
This commit is contained in:
Chris Lattner 2007-05-23 07:35:22 +00:00
parent 3f44824179
commit d540c6429f
1 changed files with 9 additions and 6 deletions
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15
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -352,7 +352,10 @@ CombineTo(SDNode *N, SDOperand Res0, SDOperand Res1) {
/// 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;
@ -368,10 +371,10 @@ static char isNegatibleForFree(SDOperand Op) {
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;
@ -384,15 +387,15 @@ static char isNegatibleForFree(SDOperand Op) {
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);
}
}