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[Constraint solver] Enable favoring of disjunction constraints during solving

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Allow constraints to be favored during solving, and unwound after exiting
that particular solver scope. We're not using this yet.
This commit is contained in:
Doug Gregor
2019-03-04 22:14:24 -08:00
parent 4c16107365
commit d2c7c8d5ee
4 changed files with 42 additions and 17 deletions
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27
lib/Sema/ConstraintSystem.cpp
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@@ -1373,17 +1373,16 @@ ConstraintSystem::getTypeOfMemberReference(
// Performance hack: if there are two generic overloads, and one is
// more specialized than the other, prefer the more-specialized one.
static void tryOptimizeGenericDisjunction(ConstraintSystem &cs,
ArrayRef<OverloadChoice> choices,
OverloadChoice *&favoredChoice) {
if (favoredChoice || choices.size() != 2)
return;
OverloadChoice *ConstraintSystem::tryOptimizeGenericDisjunction(
ArrayRef<OverloadChoice> choices) {
if (choices.size() != 2)
return nullptr;
const auto &choiceA = choices[0];
const auto &choiceB = choices[1];
if (!choiceA.isDecl() || !choiceB.isDecl())
return;
return nullptr;
auto isViable = [](ValueDecl *decl) -> bool {
assert(decl);
@@ -1410,22 +1409,17 @@ static void tryOptimizeGenericDisjunction(ConstraintSystem &cs,
auto *declB = choiceB.getDecl();
if (!isViable(declA) || !isViable(declB))
return;
auto &TC = cs.TC;
auto *DC = cs.DC;
return nullptr;
switch (TC.compareDeclarations(DC, declA, declB)) {
case Comparison::Better:
favoredChoice = const_cast<OverloadChoice *>(&choiceA);
break;
return const_cast<OverloadChoice *>(&choiceA);
case Comparison::Worse:
favoredChoice = const_cast<OverloadChoice *>(&choiceB);
break;
return const_cast<OverloadChoice *>(&choiceB);
case Comparison::Unordered:
break;
return nullptr;
}
}
@@ -1582,7 +1576,8 @@ void ConstraintSystem::addOverloadSet(Type boundType,
return;
}
tryOptimizeGenericDisjunction(*this, choices, favoredChoice);
if (!favoredChoice)
favoredChoice = tryOptimizeGenericDisjunction(choices);
SmallVector<OverloadChoice, 4> scratchChoices;
choices = partitionSIMDOperators(choices, scratchChoices);