Fix #6341: Revise purity checking #6377
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There is some confusion on terms that needs to be fixed.
Step 1: Make `SimplyPure apply to paths only.
The only point where it is used is in eta expansion to answer the question
whether in a partial application `f(e, _)` the expression `e` should be
lifted out, giving `{ val x = e; y => f(x, y) }` instead of `y => f(e, y)`.
With the change, closures and new expressions are never simply pure, so
are always lifted out. This can reduce the number of allocations, if the
lambda is applied several times.
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test performance please |
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performance test scheduled: 1 job(s) in queue, 1 running. |
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Performance test finished successfully: Visit http://dotty-bench.epfl.ch/6377/ to see the changes. Benchmarks is based on merging with master (22ba798) |
A pure expression such as `(a + b).c` of constant type is now characterized again as a pure path (since it will be eventually replaced by that constant, which is a path). This fixes instability problems in pickling and improves inlining. For instance `assert(0 == 0)` is reduced to `()` again with this change.
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test performance please |
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performance test scheduled: 1 job(s) in queue, 1 running. |
| @@ -841,12 +858,15 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] => | |||
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| object TreeInfo { | |||
| class PurityLevel(val x: Int) extends AnyVal { | |||
| def >= (that: PurityLevel): Boolean = x >= that.x | |||
| def min(that: PurityLevel): PurityLevel = new PurityLevel(x min that.x) | |||
| def >= (that: PurityLevel): Boolean = (x & that.x) == that.x | |||
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This change in the semantics of x deserves some documentation.
| val Idempotent: PurityLevel = new PurityLevel(1) | ||
| val Impure: PurityLevel = new PurityLevel(0) | ||
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| val PurePath: PurityLevel = new PurityLevel(7) | ||
| val IdempotentPath: PurityLevel = new PurityLevel(5) |
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Maybe should be more explicit
val PurePath: PurityLevel = new PurityLevel(Path.x | Pure.x)
val IdempotentPath: PurityLevel = new PurityLevel(Path.x | Idempotent.x)
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Performance test finished successfully: Visit http://dotty-bench.epfl.ch/6377/ to see the changes. Benchmarks is based on merging with master (1521576) |
biboudis
approved these changes
Apr 29, 2019
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There is some confusion on terminology that needs to be fixed.
Step 1: Make SimplyPure apply to paths only.
The only point where it is used is in eta expansion to answer the question
whether in a partial application
f(e, _)the expressioneshould belifted out, giving
{ val x = e; y => f(x, y) }instead ofy => f(e, y).With the change, closures and new expressions are never simply pure, so
are always lifted out. This can reduce the number of allocations, if the
lambda is applied several times.
Step 2: Split the property that something is a path from the property that something is pure, or idempotent.
Step 3: Require an idempotent path in the critical Inliner code.