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Cache asSeenFrom results per context #26778

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a6a7c28
Cache asSeenFrom results per context
tanishiking Aug 10, 2026
0717441
Simplify asSeenFromMap and use getOrElseUpdate
tanishiking Aug 12, 2026
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22 changes: 21 additions & 1 deletion compiler/src/dotty/tools/dotc/core/Contexts.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ import Uniques.*
import ast.Trees.*
import Flags.ParamAccessor
import ast.untpd
import util.{NoSource, SimpleIdentityMap, SourceFile, HashSet, WrappedSourceFile}
import util.{NoSource, SimpleIdentityMap, SourceFile, HashSet, WrappedSourceFile, HashMap}
import typer.{Implicits, ImportInfo, SearchHistory, SearchRoot, TypeAssigner, Typer, Nullables}
import inlines.Inliner
import Nullables.*
Expand Down Expand Up @@ -125,6 +125,18 @@ object Contexts {
* of all class fields of type context; allow them only in allowlisted
* classes (which should be short-lived).
*/

/** Identity-based key for the per-context `asSeenFrom` cache. */
private[dotc] final class AsfKey(val tp: Type, val pre: Type, val cls: Symbol):
override def hashCode: Int =
((System.identityHashCode(tp) * 31
+ System.identityHashCode(pre)) * 31
+ System.identityHashCode(cls))
override def equals(other: Any): Boolean = other match
case that: AsfKey =>
(tp eq that.tp) && (pre eq that.pre) && (cls eq that.cls)
case _ => false

abstract class Context(val base: ContextBase) { thiscontext =>

protected given Context = this
Expand Down Expand Up @@ -275,6 +287,13 @@ object Contexts {
None
)

/** Cache for `TypeOps.asSeenFrom` results computed in this context. */
private var asSeenFromCacheMap: HashMap[AsfKey, Type] | Null = null
private[dotc] def asSeenFromCache: HashMap[AsfKey, Type] =
if asSeenFromCacheMap == null then
asSeenFromCacheMap = HashMap()
asSeenFromCacheMap.nn

private var related: SimpleIdentityMap[Phase | SourceFile, Context] | Null = null

private def lookup(key: Phase | SourceFile): Context | Null =
Expand Down Expand Up @@ -551,6 +570,7 @@ object Contexts {
protected def resetCaches(): Unit =
implicitsCache = null
related = null
asSeenFromCacheMap = null

/** Reuse this context as a fresh context nested inside `outer`
* But keep the typerstate, this one has to be set explicitly if needed.
Expand Down
11 changes: 10 additions & 1 deletion compiler/src/dotty/tools/dotc/core/TypeOps.scala
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Expand Up @@ -53,7 +53,16 @@ object TypeOps:
case _ =>
}

new AsSeenFromMap(pre, cls).apply(tp)
if tp.isProvisional || pre.isProvisional then
new AsSeenFromMap(pre, cls).apply(tp)
else
var hit = true
val res = ctx.asSeenFromCache.getOrElseUpdate(AsfKey(tp, pre, cls), {
hit = false
new AsSeenFromMap(pre, cls).apply(tp)
})
Stats.record(if hit then "asSeenFrom cache hit" else "asSeenFrom cache miss")
res
}

/** The TypeMap handling the asSeenFrom */
Expand Down
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