Implement copy propagation #25
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lrytz
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Copy propagation uses an AliasingAnalyzer: it replaces a `LOAD n` instruction by `LOAD m` where m is the smallest alias of n. This leads to stale STORE instructions. Stale STOREs are identified using a ProdCons analyzer and replaced by POPs. Values that are pushed on the stack by a side-effect free instruction and consumed by a POP are then removed by `eliminatePushPop`. This includes elimination of unused closure allocations and unused boxes and tuple allocations (*). A final cleanup eliminates `STORE x; LOADx` pairs where the stored value is not otherwise used. Fixes - scala/scala-dev#25 - scala/scala-dev#7 - scala/scala-dev#14 - scala/scala-dev#12 (*) We don't yet rewrite reads of boxes and tuples yet. For example, `val x = (1, 2); x._1` remains a method invocation and the tuple cannot be eliminated (scala/scala-dev#11). Inspired in many ways by Miguel's work!
lrytz
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Nov 10, 2015
Copy propagation uses an AliasingAnalyzer: it replaces a `LOAD n` instruction by `LOAD m` where m is the smallest alias of n. This leads to stale STORE instructions. Stale STOREs are identified using a ProdCons analyzer and replaced by POPs. Values that are pushed on the stack by a side-effect free instruction and consumed by a POP are then removed by `eliminatePushPop`. This includes elimination of unused closure allocations and unused boxes and tuple allocations (*). A final cleanup eliminates `STORE x; LOADx` pairs where the stored value is not otherwise used. Fixes - scala/scala-dev#25 - scala/scala-dev#7 - scala/scala-dev#14 - scala/scala-dev#12 (*) We don't yet rewrite reads of boxes and tuples yet. For example, `val x = (1, 2); x._1` remains a method invocation and the tuple cannot be eliminated (scala/scala-dev#11). Inspired in many ways by Miguel's work!
lrytz
added a commit
to lrytz/scala
that referenced
this issue
Nov 10, 2015
Copy propagation uses an AliasingAnalyzer: it replaces a `LOAD n` instruction by `LOAD m` where m is the smallest alias of n. This leads to stale STORE instructions. Stale STOREs are identified using a ProdCons analyzer and replaced by POPs. Values that are pushed on the stack by a side-effect free instruction and consumed by a POP are then removed by `eliminatePushPop`. This includes elimination of unused closure allocations and unused boxes and tuple allocations (*). A final cleanup eliminates `STORE x; LOADx` pairs where the stored value is not otherwise used. Fixes - scala/scala-dev#25 - scala/scala-dev#7 - scala/scala-dev#14 - scala/scala-dev#12 (*) We don't yet rewrite reads of boxes and tuples yet. For example, `val x = (1, 2); x._1` remains a method invocation and the tuple cannot be eliminated (scala/scala-dev#11). Inspired in many ways by Miguel's work!
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Miguel's code: https://github.com/lrytz/scala/blob/opt/rebaseWip/src/compiler/scala/tools/nsc/backend/bcode/CopyPropagator.java
creates stale local variables that can be eliminated (#7)
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