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Refactor pattern matching in global init checker, skipping cases when safe to do so #22179

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Refactor pattern matching in global init checker, skipping cases when safe to do so #22179

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fcded74
Refactor pattern matching, skipping cases when safe to do so
Nov 22, 2024
49b8d44
Add BaseOrUnknownValue
Dec 14, 2024
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115 changes: 81 additions & 34 deletions compiler/src/dotty/tools/dotc/transform/init/Objects.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@ import util.{ SourcePosition, NoSourcePosition }
import config.Printers.init as printer
import reporting.StoreReporter
import reporting.trace as log
import reporting.trace.force as forcelog
import typer.Applications.*

import Errors.*
Expand Down Expand Up @@ -91,6 +92,7 @@ class Objects(using Context @constructorOnly):
* ve ::= ObjectRef(class) // global object
* | OfClass(class, vs[outer], ctor, args, env) // instance of a class
* | OfArray(object[owner], regions)
* | BaseOrUnknownValue // Int, String, etc., and values without source
* | Fun(..., env) // value elements that can be contained in ValueSet
* vs ::= ValueSet(ve) // set of abstract values
* Bottom ::= ValueSet(Empty)
Expand Down Expand Up @@ -233,6 +235,11 @@ class Objects(using Context @constructorOnly):
case class ValueSet(values: ListSet[ValueElement]) extends Value:
def show(using Context) = values.map(_.show).mkString("[", ",", "]")

// Represents common base values like Int, String, etc.
// and also values loaded without source
case object BaseOrUnknownValue extends ValueElement:
def show(using Context): String = "BaseOrUnknownValue"

/** A cold alias which should not be used during initialization.
*
* Cold is not ValueElement since RefSet containing Cold is equivalent to Cold
Expand Down Expand Up @@ -602,6 +609,12 @@ class Objects(using Context @constructorOnly):
case (ValueSet(values), b : ValueElement) => ValueSet(values + b)
case (a : ValueElement, b : ValueElement) => ValueSet(ListSet(a, b))

def remove(b: Value): Value = (a, b) match
case (ValueSet(values1), b: ValueElement) => ValueSet(values1 - b)
case (ValueSet(values1), ValueSet(values2)) => ValueSet(values1.removedAll(values2))
case (a: Ref, b: Ref) if a.equals(b) => Bottom
case _ => a

def widen(height: Int)(using Context): Value =
if height == 0 then Cold
else
Expand Down Expand Up @@ -630,12 +643,15 @@ class Objects(using Context @constructorOnly):
if baseClasses.isEmpty then a
else filterClass(baseClasses.head) // could have called ClassSymbol, but it does not handle OrType and AndType

// Filter the value according to a class symbol, and only leaves the sub-values
// which could represent an object of the given class
def filterClass(sym: Symbol)(using Context): Value =
if !sym.isClass then a
else
val klass = sym.asClass
a match
case Cold => Cold
case BaseOrUnknownValue => BaseOrUnknownValue
case ref: Ref => if ref.klass.isSubClass(klass) then ref else Bottom
case ValueSet(values) => values.map(v => v.filterClass(klass)).join
case arr: OfArray => if defn.ArrayClass.isSubClass(klass) then arr else Bottom
Expand Down Expand Up @@ -668,6 +684,13 @@ class Objects(using Context @constructorOnly):
case Bottom =>
Bottom

// Bottom arguments mean unreachable call
case _ if args.map(_.value).contains(Bottom) =>
Bottom

case BaseOrUnknownValue =>
BaseOrUnknownValue

case arr: OfArray =>
val target = resolve(defn.ArrayClass, meth)

Expand All @@ -686,7 +709,7 @@ class Objects(using Context @constructorOnly):
Bottom
else
// Array.length is OK
Bottom
BaseOrUnknownValue

case ref: Ref =>
val isLocal = !meth.owner.isClass
Expand All @@ -707,7 +730,7 @@ class Objects(using Context @constructorOnly):
arr
else if target.equals(defn.Predef_classOf) then
// Predef.classOf is a stub method in tasty and is replaced in backend
Bottom
BaseOrUnknownValue
else if target.hasSource then
val cls = target.owner.enclosingClass.asClass
val ddef = target.defTree.asInstanceOf[DefDef]
Expand All @@ -730,7 +753,7 @@ class Objects(using Context @constructorOnly):
}
}
else
Bottom
BaseOrUnknownValue
else if target.exists then
select(ref, target, receiver, needResolve = false)
else
Expand Down Expand Up @@ -798,7 +821,7 @@ class Objects(using Context @constructorOnly):
}
else
// no source code available
Bottom
BaseOrUnknownValue

case _ =>
report.warning("[Internal error] unexpected constructor call, meth = " + ctor + ", this = " + value + Trace.show, Trace.position)
Expand All @@ -818,6 +841,9 @@ class Objects(using Context @constructorOnly):
report.warning("Using cold alias", Trace.position)
Bottom

case BaseOrUnknownValue =>
BaseOrUnknownValue

case ref: Ref =>
val target = if needResolve then resolve(ref.klass, field) else field
if target.is(Flags.Lazy) then
Expand All @@ -826,7 +852,7 @@ class Objects(using Context @constructorOnly):
val rhs = target.defTree.asInstanceOf[ValDef].rhs
eval(rhs, ref, target.owner.asClass, cacheResult = true)
else
Bottom
BaseOrUnknownValue
else if target.exists then
def isNextFieldOfColonColon: Boolean = ref.klass == defn.ConsClass && target.name.toString == "next"
if target.isOneOf(Flags.Mutable) && !isNextFieldOfColonColon then
Expand All @@ -842,24 +868,24 @@ class Objects(using Context @constructorOnly):
Bottom
else
// initialization error, reported by the initialization checker
Bottom
BaseOrUnknownValue
else if ref.hasVal(target) then
ref.valValue(target)
else if ref.isObjectRef && ref.klass.hasSource then
report.warning("Access uninitialized field " + field.show + ". " + Trace.show, Trace.position)
Bottom
else
// initialization error, reported by the initialization checker
Bottom
BaseOrUnknownValue

else
if ref.klass.isSubClass(receiver.widenSingleton.classSymbol) then
report.warning("[Internal error] Unexpected resolution failure: ref.klass = " + ref.klass.show + ", field = " + field.show + Trace.show, Trace.position)
Bottom
else
// This is possible due to incorrect type cast.
// See tests/init/pos/Type.scala
Bottom
// This is possible due to incorrect type cast or accessing standard library objects
// See tests/init/pos/Type.scala / tests/init/warn/unapplySeq-implicit-arg2.scala
BaseOrUnknownValue

case fun: Fun =>
report.warning("[Internal error] unexpected tree in selecting a function, fun = " + fun.code.show + Trace.show, fun.code)
Expand All @@ -869,7 +895,7 @@ class Objects(using Context @constructorOnly):
report.warning("[Internal error] unexpected tree in selecting an array, array = " + arr.show + Trace.show, Trace.position)
Bottom

case Bottom =>
case Bottom => // TODO: add a value for packages?
if field.isStaticObject then accessObject(field.moduleClass.asClass)
else Bottom

Expand All @@ -895,7 +921,7 @@ class Objects(using Context @constructorOnly):
case Cold =>
report.warning("Assigning to cold aliases is forbidden. " + Trace.show, Trace.position)

case Bottom =>
case BaseOrUnknownValue | Bottom =>

case ValueSet(values) =>
values.foreach(ref => assign(ref, field, rhs, rhsTyp))
Expand Down Expand Up @@ -930,6 +956,9 @@ class Objects(using Context @constructorOnly):
report.warning("[Internal error] unexpected outer in instantiating a class, outer = " + outer.show + ", class = " + klass.show + ", " + Trace.show, Trace.position)
Bottom

case BaseOrUnknownValue =>
BaseOrUnknownValue

case outer: (Ref | Cold.type | Bottom.type) =>
if klass == defn.ArrayClass then
args.head.tree.tpe match
Expand Down Expand Up @@ -1018,6 +1047,7 @@ class Objects(using Context @constructorOnly):
case Cold =>
report.warning("Calling cold by-name alias. " + Trace.show, Trace.position)
Bottom
case BaseOrUnknownValue => BaseOrUnknownValue
case _: ValueSet | _: Ref | _: OfArray =>
report.warning("[Internal error] Unexpected by-name value " + value.show + ". " + Trace.show, Trace.position)
Bottom
Expand Down Expand Up @@ -1206,7 +1236,7 @@ class Objects(using Context @constructorOnly):
evalType(expr.tpe, thisV, klass)

case Literal(_) =>
Bottom
BaseOrUnknownValue

case Typed(expr, tpt) =>
if tpt.tpe.hasAnnotation(defn.UncheckedAnnot) then
Expand Down Expand Up @@ -1341,29 +1371,25 @@ class Objects(using Context @constructorOnly):
def getMemberMethod(receiver: Type, name: TermName, tp: Type): Denotation =
receiver.member(name).suchThat(receiver.memberInfo(_) <:< tp)

def evalCase(caseDef: CaseDef): Value =
evalPattern(scrutinee, caseDef.pat)
eval(caseDef.guard, thisV, klass)
eval(caseDef.body, thisV, klass)

/** Abstract evaluation of patterns.
*
* It augments the local environment for bound pattern variables. As symbols are globally
* unique, we can put them in a single environment.
*
* Currently, we assume all cases are reachable, thus all patterns are assumed to match.
*/
def evalPattern(scrutinee: Value, pat: Tree): Value = log("match " + scrutinee.show + " against " + pat.show, printer, (_: Value).show):
def evalPattern(scrutinee: Value, pat: Tree): (Type, Value) = log("match " + scrutinee.show + " against " + pat.show, printer, (_: (Type, Value))._2.show):
val trace2 = Trace.trace.add(pat)
pat match
case Alternative(pats) =>
for pat <- pats do evalPattern(scrutinee, pat)
scrutinee
val (types, values) = pats.map(evalPattern(scrutinee, _)).unzip()
val orType = types.fold(defn.NothingType)(OrType(_, _, false))
(orType, values.join)

case bind @ Bind(_, pat) =>
val value = evalPattern(scrutinee, pat)
val (tpe, value) = evalPattern(scrutinee, pat)
initLocal(bind.symbol, value)
scrutinee
(tpe, value)

case UnApply(fun, implicits, pats) =>
given Trace = trace2
Expand All @@ -1372,6 +1398,10 @@ class Objects(using Context @constructorOnly):
val funRef = fun1.tpe.asInstanceOf[TermRef]
val unapplyResTp = funRef.widen.finalResultType

val receiverType = fun1 match
case ident: Ident => funRef.prefix
case select: Select => select.qualifier.tpe

val receiver = fun1 match
case ident: Ident =>
evalType(funRef.prefix, thisV, klass)
Expand Down Expand Up @@ -1460,17 +1490,20 @@ class Objects(using Context @constructorOnly):
end if
end if
end if
scrutinee
// TODO: receiverType is the companion object type, not the class itself;
// cannot filter scritunee by this type
(receiverType, scrutinee)

case Ident(nme.WILDCARD) | Ident(nme.WILDCARD_STAR) =>
scrutinee
(defn.ThrowableType, scrutinee)

case Typed(pat, _) =>
evalPattern(scrutinee, pat)
case Typed(pat, typeTree) =>
val (_, value) = evalPattern(scrutinee.filterType(typeTree.tpe), pat)
(typeTree.tpe, value)

case tree =>
// For all other trees, the semantics is normal.
eval(tree, thisV, klass)
(defn.ThrowableType, eval(tree, thisV, klass))

end evalPattern

Expand All @@ -1481,15 +1514,15 @@ class Objects(using Context @constructorOnly):
// call .lengthCompare or .length
val lengthCompareDenot = getMemberMethod(scrutineeType, nme.lengthCompare, lengthCompareType)
if lengthCompareDenot.exists then
call(scrutinee, lengthCompareDenot.symbol, ArgInfo(Bottom, summon[Trace], EmptyTree) :: Nil, scrutineeType, superType = NoType, needResolve = true)
call(scrutinee, lengthCompareDenot.symbol, ArgInfo(BaseOrUnknownValue, summon[Trace], EmptyTree) :: Nil, scrutineeType, superType = NoType, needResolve = true)
else
val lengthDenot = getMemberMethod(scrutineeType, nme.length, lengthType)
call(scrutinee, lengthDenot.symbol, Nil, scrutineeType, superType = NoType, needResolve = true)
end if

// call .apply
val applyDenot = getMemberMethod(scrutineeType, nme.apply, applyType(elemType))
val applyRes = call(scrutinee, applyDenot.symbol, ArgInfo(Bottom, summon[Trace], EmptyTree) :: Nil, scrutineeType, superType = NoType, needResolve = true)
val applyRes = call(scrutinee, applyDenot.symbol, ArgInfo(BaseOrUnknownValue, summon[Trace], EmptyTree) :: Nil, scrutineeType, superType = NoType, needResolve = true)

if isWildcardStarArgList(pats) then
if pats.size == 1 then
Expand All @@ -1500,7 +1533,7 @@ class Objects(using Context @constructorOnly):
else
// call .drop
val dropDenot = getMemberMethod(scrutineeType, nme.drop, dropType(elemType))
val dropRes = call(scrutinee, dropDenot.symbol, ArgInfo(Bottom, summon[Trace], EmptyTree) :: Nil, scrutineeType, superType = NoType, needResolve = true)
val dropRes = call(scrutinee, dropDenot.symbol, ArgInfo(BaseOrUnknownValue, summon[Trace], EmptyTree) :: Nil, scrutineeType, superType = NoType, needResolve = true)
for pat <- pats.init do evalPattern(applyRes, pat)
evalPattern(dropRes, pats.last)
end if
Expand All @@ -1510,8 +1543,21 @@ class Objects(using Context @constructorOnly):
end if
end evalSeqPatterns

def canSkipCase(remainingScrutinee: Value, catchValue: Value) =
(remainingScrutinee == Bottom && scrutinee != Bottom) ||
(catchValue == Bottom && remainingScrutinee != Bottom)

cases.map(evalCase).join
var remainingScrutinee = scrutinee
val caseResults: mutable.ArrayBuffer[Value] = mutable.ArrayBuffer()
for caseDef <- cases do
val (tpe, value) = evalPattern(remainingScrutinee, caseDef.pat)
eval(caseDef.guard, thisV, klass)
if !canSkipCase(remainingScrutinee, value) then
caseResults.addOne(eval(caseDef.body, thisV, klass))
if catchesAllOf(caseDef, tpe) then
remainingScrutinee = remainingScrutinee.remove(value)

caseResults.join
end patternMatch

/** Handle semantics of leaf nodes
Expand All @@ -1529,12 +1575,12 @@ class Objects(using Context @constructorOnly):
def evalType(tp: Type, thisV: ThisValue, klass: ClassSymbol, elideObjectAccess: Boolean = false): Contextual[Value] = log("evaluating " + tp.show, printer, (_: Value).show) {
tp match
case _: ConstantType =>
Bottom
BaseOrUnknownValue

case tmref: TermRef if tmref.prefix == NoPrefix =>
val sym = tmref.symbol
if sym.is(Flags.Package) then
Bottom
Bottom // TODO: package value?
else if sym.owner.isClass then
// The typer incorrectly assigns a TermRef with NoPrefix for `config`,
// while the actual denotation points to the symbol of the class member
Expand Down Expand Up @@ -1768,6 +1814,7 @@ class Objects(using Context @constructorOnly):
else
thisV match
case Bottom => Bottom
case BaseOrUnknownValue => BaseOrUnknownValue
case Cold => Cold
case ref: Ref =>
val outerCls = klass.owner.lexicallyEnclosingClass.asClass
Expand Down
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