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Fix isNegatibleForFree to not return true for ConstantFP nodes 

after legalize.  Just because a constant is legal (e.g. 0.0 in SSE) 
doesn't mean that its negated value is legal (-0.0).  We could make
this stronger by checking to see if the negated constant is actually
legal post negation, but it doesn't seem like a big deal.

llvm-svn: 47591
This commit is contained in:
Chris Lattner 2008-02-26 07:04:54 +00:00
parent ce3563445c
commit e7c14013f5
2 changed files with 61 additions and 33 deletions
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80
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -306,7 +306,8 @@ 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, unsigned Depth = 0) {
static char isNegatibleForFree(SDOperand Op, bool AfterLegalize,
unsigned Depth = 0) {
// No compile time optimizations on this type.
if (Op.getValueType() == MVT::ppcf128)
return 0;
@ -323,16 +324,18 @@ static char isNegatibleForFree(SDOperand Op, unsigned Depth = 0) {
switch (Op.getOpcode()) {
default: return false;
case ISD::ConstantFP:
return 1;
// Don't invert constant FP values after legalize. The negated constant
// isn't necessarily legal.
return AfterLegalize ? 0 : 1;
case ISD::FADD:
// FIXME: determine better conditions for this xform.
if (!UnsafeFPMath) return 0;
// -(A+B) -> -A - B
if (char V = isNegatibleForFree(Op.getOperand(0), Depth+1))
if (char V = isNegatibleForFree(Op.getOperand(0), AfterLegalize, Depth+1))
return V;
// -(A+B) -> -B - A
return isNegatibleForFree(Op.getOperand(1), Depth+1);
return isNegatibleForFree(Op.getOperand(1), AfterLegalize, Depth+1);
case ISD::FSUB:
// We can't turn -(A-B) into B-A when we honor signed zeros.
if (!UnsafeFPMath) return 0;
@ -345,22 +348,22 @@ static char isNegatibleForFree(SDOperand Op, unsigned Depth = 0) {
if (HonorSignDependentRoundingFPMath()) return 0;
// -(X*Y) -> (-X * Y) or (X*-Y)
if (char V = isNegatibleForFree(Op.getOperand(0), Depth+1))
if (char V = isNegatibleForFree(Op.getOperand(0), AfterLegalize, Depth+1))
return V;
return isNegatibleForFree(Op.getOperand(1), Depth+1);
return isNegatibleForFree(Op.getOperand(1), AfterLegalize, Depth+1);
case ISD::FP_EXTEND:
case ISD::FP_ROUND:
case ISD::FSIN:
return isNegatibleForFree(Op.getOperand(0), Depth+1);
return isNegatibleForFree(Op.getOperand(0), AfterLegalize, Depth+1);
}
}
/// GetNegatedExpression - If isNegatibleForFree returns true, this function
/// returns the newly negated expression.
static SDOperand GetNegatedExpression(SDOperand Op, SelectionDAG &DAG,
unsigned Depth = 0) {
bool AfterLegalize, unsigned Depth = 0) {
// fneg is removable even if it has multiple uses.
if (Op.getOpcode() == ISD::FNEG) return Op.getOperand(0);
@ -380,13 +383,15 @@ static SDOperand GetNegatedExpression(SDOperand Op, SelectionDAG &DAG,
assert(UnsafeFPMath);
// -(A+B) -> -A - B
if (isNegatibleForFree(Op.getOperand(0), Depth+1))
if (isNegatibleForFree(Op.getOperand(0), AfterLegalize, Depth+1))
return DAG.getNode(ISD::FSUB, Op.getValueType(),
GetNegatedExpression(Op.getOperand(0), DAG, Depth+1),
GetNegatedExpression(Op.getOperand(0), DAG,
AfterLegalize, Depth+1),
Op.getOperand(1));
// -(A+B) -> -B - A
return DAG.getNode(ISD::FSUB, Op.getValueType(),
GetNegatedExpression(Op.getOperand(1), DAG, Depth+1),
GetNegatedExpression(Op.getOperand(1), DAG,
AfterLegalize, Depth+1),
Op.getOperand(0));
case ISD::FSUB:
// We can't turn -(A-B) into B-A when we honor signed zeros.
@ -408,21 +413,25 @@ static SDOperand GetNegatedExpression(SDOperand Op, SelectionDAG &DAG,
// -(X*Y) -> -X * Y
if (isNegatibleForFree(Op.getOperand(0), Depth+1))
return DAG.getNode(Op.getOpcode(), Op.getValueType(),
GetNegatedExpression(Op.getOperand(0), DAG, Depth+1),
GetNegatedExpression(Op.getOperand(0), DAG,
AfterLegalize, Depth+1),
Op.getOperand(1));
// -(X*Y) -> X * -Y
return DAG.getNode(Op.getOpcode(), Op.getValueType(),
Op.getOperand(0),
GetNegatedExpression(Op.getOperand(1), DAG, Depth+1));
GetNegatedExpression(Op.getOperand(1), DAG,
AfterLegalize, Depth+1));
case ISD::FP_EXTEND:
case ISD::FSIN:
return DAG.getNode(Op.getOpcode(), Op.getValueType(),
GetNegatedExpression(Op.getOperand(0), DAG, Depth+1));
GetNegatedExpression(Op.getOperand(0), DAG,
AfterLegalize, Depth+1));
case ISD::FP_ROUND:
return DAG.getNode(ISD::FP_ROUND, Op.getValueType(),
GetNegatedExpression(Op.getOperand(0), DAG, Depth+1),
GetNegatedExpression(Op.getOperand(0), DAG,
AfterLegalize, Depth+1),
Op.getOperand(1));
}
}
@ -3518,11 +3527,13 @@ SDOperand DAGCombiner::visitFADD(SDNode *N) {
if (N0CFP && !N1CFP)
return DAG.getNode(ISD::FADD, VT, N1, N0);
// fold (A + (-B)) -> A-B
if (isNegatibleForFree(N1) == 2)
return DAG.getNode(ISD::FSUB, VT, N0, GetNegatedExpression(N1, DAG));
if (isNegatibleForFree(N1, AfterLegalize) == 2)
return DAG.getNode(ISD::FSUB, VT, N0,
GetNegatedExpression(N1, DAG, AfterLegalize));
// fold ((-A) + B) -> B-A
if (isNegatibleForFree(N0) == 2)
return DAG.getNode(ISD::FSUB, VT, N1, GetNegatedExpression(N0, DAG));
if (isNegatibleForFree(N0, AfterLegalize) == 2)
return DAG.getNode(ISD::FSUB, VT, N1,
GetNegatedExpression(N0, DAG, AfterLegalize));
// If allowed, fold (fadd (fadd x, c1), c2) -> (fadd x, (fadd c1, c2))
if (UnsafeFPMath && N1CFP && N0.getOpcode() == ISD::FADD &&
@ -3551,13 +3562,14 @@ SDOperand DAGCombiner::visitFSUB(SDNode *N) {
return DAG.getNode(ISD::FSUB, VT, N0, N1);
// fold (0-B) -> -B
if (UnsafeFPMath && N0CFP && N0CFP->getValueAPF().isZero()) {
if (isNegatibleForFree(N1))
return GetNegatedExpression(N1, DAG);
if (isNegatibleForFree(N1, AfterLegalize))
return GetNegatedExpression(N1, DAG, AfterLegalize);
return DAG.getNode(ISD::FNEG, VT, N1);
}
// fold (A-(-B)) -> A+B
if (isNegatibleForFree(N1))
return DAG.getNode(ISD::FADD, VT, N0, GetNegatedExpression(N1, DAG));
if (isNegatibleForFree(N1, AfterLegalize))
return DAG.getNode(ISD::FADD, VT, N0,
GetNegatedExpression(N1, DAG, AfterLegalize));
return SDOperand();
}
@ -3589,13 +3601,14 @@ SDOperand DAGCombiner::visitFMUL(SDNode *N) {
return DAG.getNode(ISD::FNEG, VT, N0);
// -X * -Y -> X*Y
if (char LHSNeg = isNegatibleForFree(N0)) {
if (char RHSNeg = isNegatibleForFree(N1)) {
if (char LHSNeg = isNegatibleForFree(N0, AfterLegalize)) {
if (char RHSNeg = isNegatibleForFree(N1, AfterLegalize)) {
// Both can be negated for free, check to see if at least one is cheaper
// negated.
if (LHSNeg == 2 || RHSNeg == 2)
return DAG.getNode(ISD::FMUL, VT, GetNegatedExpression(N0, DAG),
GetNegatedExpression(N1, DAG));
return DAG.getNode(ISD::FMUL, VT,
GetNegatedExpression(N0, DAG, AfterLegalize),
GetNegatedExpression(N1, DAG, AfterLegalize));
}
}
@ -3627,13 +3640,14 @@ SDOperand DAGCombiner::visitFDIV(SDNode *N) {
// -X / -Y -> X*Y
if (char LHSNeg = isNegatibleForFree(N0)) {
if (char RHSNeg = isNegatibleForFree(N1)) {
if (char LHSNeg = isNegatibleForFree(N0, AfterLegalize)) {
if (char RHSNeg = isNegatibleForFree(N1, AfterLegalize)) {
// Both can be negated for free, check to see if at least one is cheaper
// negated.
if (LHSNeg == 2 || RHSNeg == 2)
return DAG.getNode(ISD::FDIV, VT, GetNegatedExpression(N0, DAG),
GetNegatedExpression(N1, DAG));
return DAG.getNode(ISD::FDIV, VT,
GetNegatedExpression(N0, DAG, AfterLegalize),
GetNegatedExpression(N1, DAG, AfterLegalize));
}
}
@ -3837,8 +3851,8 @@ SDOperand DAGCombiner::visitFP_EXTEND(SDNode *N) {
SDOperand DAGCombiner::visitFNEG(SDNode *N) {
SDOperand N0 = N->getOperand(0);
if (isNegatibleForFree(N0))
return GetNegatedExpression(N0, DAG);
if (isNegatibleForFree(N0, AfterLegalize))
return GetNegatedExpression(N0, DAG, AfterLegalize);
// Transform fneg(bitconvert(x)) -> bitconvert(x^sign) to avoid loading
// constant pool values.

14
llvm/test/CodeGen/Generic/2008-02-25-NegateZero.ll Normal file
View File

@ -0,0 +1,14 @@
; RUN: llvm-as < %s | llc
; rdar://5763967
define void @test() {
entry:
%tmp98 = load float* null, align 4 ; <float> [#uses=1]
%tmp106 = load float* null, align 4 ; <float> [#uses=1]
%tmp113 = add float %tmp98, %tmp106 ; <float> [#uses=1]
%tmp119 = sub float %tmp113, 0.000000e+00 ; <float> [#uses=1]
call void (i32, ...)* @foo( i32 0, float 0.000000e+00, float %tmp119 ) nounwind
ret void
}
declare void @foo(i32, ...)