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[SCEV] Separate out constant folding in mul expr creation 

Separate out the code handling constant folding into a separate
block, that is independent of other folds that need a constant
first operand. Also make some minor adjustments to make the
constant folding look nearly identical to the same code in
getAddExpr().

The only reason this change is not strictly NFC is that the
C1*(C2+V) fold is moved below the constant folding, which means
that it now also applies to C1*C2*(C3+V), as it should.
This commit is contained in:
Nikita Popov 2020-10-25 18:14:20 +01:00
parent 0dda633317
commit 22a5cde541
1 changed files with 28 additions and 26 deletions
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54
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -2700,8 +2700,32 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
// If there are any constants, fold them together.
unsigned Idx = 0;
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) {
++Idx;
assert(Idx < Ops.size());
while (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) {
// We found two constants, fold them together!
Ops[0] = getConstant(LHSC->getAPInt() * RHSC->getAPInt());
if (Ops.size() == 2) return Ops[0];
Ops.erase(Ops.begin()+1); // Erase the folded element
LHSC = cast<SCEVConstant>(Ops[0]);
}
if (Ops.size() == 2)
// If we have a multiply of zero, it will always be zero.
if (LHSC->getValue()->isZero())
return LHSC;
// If we are left with a constant one being multiplied, strip it off.
if (LHSC->getValue()->isOne()) {
Ops.erase(Ops.begin());
--Idx;
}
if (Ops.size() == 1)
return Ops[0];
}
if (const SCEVConstant *LHSC = dyn_cast<SCEVConstant>(Ops[0])) {
if (Ops.size() == 2) {
// C1*(C2+V) -> C1*C2 + C1*V
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1]))
// If any of Add's ops are Adds or Muls with a constant, apply this
@ -2717,28 +2741,9 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
SCEV::FlagAnyWrap, Depth + 1),
SCEV::FlagAnyWrap, Depth + 1);
++Idx;
while (const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(Ops[Idx])) {
// We found two constants, fold them together!
ConstantInt *Fold =
ConstantInt::get(getContext(), LHSC->getAPInt() * RHSC->getAPInt());
Ops[0] = getConstant(Fold);
Ops.erase(Ops.begin()+1); // Erase the folded element
if (Ops.size() == 1) return Ops[0];
LHSC = cast<SCEVConstant>(Ops[0]);
}
// If we are left with a constant one being multiplied, strip it off.
if (cast<SCEVConstant>(Ops[0])->getValue()->isOne()) {
Ops.erase(Ops.begin());
--Idx;
} else if (cast<SCEVConstant>(Ops[0])->getValue()->isZero()) {
// If we have a multiply of zero, it will always be zero.
return Ops[0];
} else if (Ops[0]->isAllOnesValue()) {
// If we have a mul by -1 of an add, try distributing the -1 among the
// add operands.
if (Ops.size() == 2) {
if (Ops[0]->isAllOnesValue()) {
// If we have a mul by -1 of an add, try distributing the -1 among the
// add operands.
if (const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(Ops[1])) {
SmallVector<const SCEV *, 4> NewOps;
bool AnyFolded = false;
@ -2762,9 +2767,6 @@ const SCEV *ScalarEvolution::getMulExpr(SmallVectorImpl<const SCEV *> &Ops,
}
}
}
if (Ops.size() == 1)
return Ops[0];
}
// Skip over the add expression until we get to a multiply.