0000509: higher_order.m optimizes soon-to-be-dead procedures

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0000509

mercury

Bug

public

2020-06-16 02:47

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Assigned To

Priority

normal

Severity

minor

Reproducibility

have not tried

Status

assigned

Resolution

open

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Summary

0000509: higher_order.m optimizes soon-to-be-dead procedures

Description

When the compiler has read in a bunch of predicate/function definitions from .opt files,
those definitions get added to set of valid preds. higher_order.m looks for optimization
opportunities among the set of valid preds. However, the common case is that
those .opt files contain a whole bunch of predicates of which the current module
uses only a few either directly or indirectly. (When have you written any module
that calls all or even most of the predicates exported from e.g. list.m or map.m?)
Optimizing the predicates that one of the following compiler passes will soon delete
as dead code is a performance bug.

We should modify either higher_order.m or its caller to delete dead procedures
from the HLDS before it starts its work.

Note that we will still need to do a round of dead proc elimination *after* higher_order.m,
since higher_order.m can sometimes replace all calls to a predicate with calls to a
specialized version, which makes the original version obsolete. However, maybe
this could be done by higher_order.m itself *faster* than dead_proc_elim.m could
do it, since it should be possible to avoid the need to construct a full call graph
to do the job; counting unspecialized call sites should do the job.

Date Modified	Username	Field	Change
Issue History
2020-06-16 02:47	zs	New Issue
2020-06-16 02:47	zs	Status	new => assigned
2020-06-16 02:47	zs	Assigned To	=> zs

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