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Fix a problem that Nate noticed that boils down to an over conservative check 

in the code that does "select C, (X+Y), (X-Y) --> (X+(select C, Y, (-Y)))".
We now compile this loop:

LBB1_1: ; no_exit
        add r6, r2, r3
        subf r3, r2, r3
        cmpwi cr0, r2, 0
        addi r7, r5, 4
        lwz r2, 0(r5)
        addi r4, r4, 1
        blt cr0, LBB1_4 ; no_exit
LBB1_3: ; no_exit
        mr r3, r6
LBB1_4: ; no_exit
        cmpwi cr0, r4, 16
        mr r5, r7
        bne cr0, LBB1_1 ; no_exit

into this instead:

LBB1_1: ; no_exit
        srawi r6, r2, 31
        add r2, r2, r6
        xor r6, r2, r6
        addi r7, r5, 4
        lwz r2, 0(r5)
        addi r4, r4, 1
        add r3, r3, r6
        cmpwi cr0, r4, 16
        mr r5, r7
        bne cr0, LBB1_1 ; no_exit

llvm-svn: 26356
This commit is contained in:
Chris Lattner 2006-02-24 18:05:58 +00:00
parent 723d3e0746
commit b580d26e7d
1 changed files with 18 additions and 23 deletions
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41
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -5074,30 +5074,25 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
}
if (OtherAddOp) {
// So at this point we know we have:
// select C, (add X, Y), (sub X, ?)
// We can do the transform profitably if either 'Y' = '?' or '?' is
// a constant.
if (SubOp->getOperand(1) == AddOp ||
isa<Constant>(SubOp->getOperand(1))) {
Value *NegVal;
if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) {
NegVal = ConstantExpr::getNeg(C);
} else {
NegVal = InsertNewInstBefore(
BinaryOperator::createNeg(SubOp->getOperand(1)), SI);
}
Value *NewTrueOp = OtherAddOp;
Value *NewFalseOp = NegVal;
if (AddOp != TI)
std::swap(NewTrueOp, NewFalseOp);
Instruction *NewSel =
new SelectInst(CondVal, NewTrueOp,NewFalseOp,SI.getName()+".p");
NewSel = InsertNewInstBefore(NewSel, SI);
return BinaryOperator::createAdd(SubOp->getOperand(0), NewSel);
// So at this point we know we have (Y -> OtherAddOp):
// select C, (add X, Y), (sub X, Z)
Value *NegVal; // Compute -Z
if (Constant *C = dyn_cast<Constant>(SubOp->getOperand(1))) {
NegVal = ConstantExpr::getNeg(C);
} else {
NegVal = InsertNewInstBefore(
BinaryOperator::createNeg(SubOp->getOperand(1), "tmp"), SI);
}
Value *NewTrueOp = OtherAddOp;
Value *NewFalseOp = NegVal;
if (AddOp != TI)
std::swap(NewTrueOp, NewFalseOp);
Instruction *NewSel =
new SelectInst(CondVal, NewTrueOp,NewFalseOp,SI.getName()+".p");
NewSel = InsertNewInstBefore(NewSel, SI);
return BinaryOperator::createAdd(SubOp->getOperand(0), NewSel);
}
}
}