excessive inlining of jump tables #7449
Comments
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Comment author: @alainfrisch Is this this flambda? I cannot reproduce in non-flambda mode, except by passing a large -inline command-line argument to ocamlopt. |
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Comment author: markghayden All my testing was with flambda-enabled compilers. |
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This issue has been open one year with no activity. Consequently, it is being marked with the "stale" label. What this means is that the issue will be automatically closed in 30 days unless more comments are added or the "stale" label is removed. Comments that provide new information on the issue are especially welcome: is it still reproducible? did it appear in other contexts? how critical is it? etc. |
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I can confirm that this bug is still present; the size estimation for switches doesn't seem to take the size of the actions into account. |
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This issue has been open one year with no activity. Consequently, it is being marked with the "stale" label. What this means is that the issue will be automatically closed in 30 days unless more comments are added or the "stale" label is removed. Comments that provide new information on the issue are especially welcome: is it still reproducible? did it appear in other contexts? how critical is it? etc. |
Original bug ID: 7449
Reporter: markghayden
Assigned to: @chambart
Status: assigned (set by @chambart on 2017-01-03T20:59:28Z)
Resolution: open
Priority: normal
Severity: minor
Platform: AMD64
OS: MacOS
OS Version: 10.12.2
Version: 4.04.0
Category: middle end (typedtree to clambda)
Tags: flambda
Monitored by: @gasche @ygrek
Bug description
See the attached code. The [to_string] function is inlined at all call sites, even with no optimization specified at the command line (!?!). Note that each call site includes a full copy of the jump table and all the jump branches. The test case here has 30 items. I've seen this with larger cases (300 items). Maybe I'm missing something, but it seems this is really off here since this behavior can result in significant code growth. A work-around is to annotate with '[@inline never]'.
Steps to reproduce
Compile with 4.04.0 or 4.05.0.dev trunk. Note that for 4.05.0.dev, the lookup table is used if all the return values are constants and perhaps that is OK to inline. Added a [failwith] for one of the cases forces the use of jump tables, at least on AMD64.
ocamlopt -c -S du.ml
Additional information
See attached ML file. Assembler output will follow.
File attachments
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