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Differential D83781

[LangRef] Fix condition for when a loop is considered parallel.
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Authored by Meinersbur on Jul 14 2020, 8:29 AM.

Details

Reviewers
mppf
jdoerfert
hfinkel
Commits
rG137dfd616aaf: [LangRef] Fix condition for when a loop is considered parallel.
Summary

The wording before this patch applies to llvm.mem.parallel_loop_access, not access groups.

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Meinersbur created this revision.Jul 14 2020, 8:29 AM
Herald added a reviewer: jdoerfert. · View Herald TranscriptJul 14 2020, 8:29 AM
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hfinkel accepted this revision.Jul 14 2020, 8:36 AM
hfinkel added a subscriber: hfinkel.

LGTM

This revision is now accepted and ready to land.Jul 14 2020, 8:36 AM
Harbormaster failed remote builds in B64162: Diff 277841!Jul 14 2020, 8:58 AM
mppf accepted this revision.Jul 14 2020, 9:00 AM

Thanks for fixing it!

This revision was landed with ongoing or failed builds.Sep 1 2020, 1:42 PM
Closed by commit rG137dfd616aaf: [LangRef] Fix condition for when a loop is considered parallel. (authored by Meinersbur). · Explain Why
This revision was automatically updated to reflect the committed changes.
Meinersbur added a commit: rG137dfd616aaf: [LangRef] Fix condition for when a loop is considered parallel..

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llvm/docs/LangRef.rst

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``g2`` (which might be identical). If a loop contains both access groups ``g2`` (which might be identical). If a loop contains both access groups
in its ``llvm.loop.parallel_accesses`` metadata, then the compiler can in its ``llvm.loop.parallel_accesses`` metadata, then the compiler can
assume that there is no dependency between ``m1`` and ``m2`` carried by assume that there is no dependency between ``m1`` and ``m2`` carried by
this loop. Instructions that belong to multiple access groups are this loop. Instructions that belong to multiple access groups are
considered having this property if at least one of the access groups considered having this property if at least one of the access groups
matches the ``llvm.loop.parallel_accesses`` list. matches the ``llvm.loop.parallel_accesses`` list.
If all memory-accessing instructions in a loop have If all memory-accessing instructions in a loop have
``llvm.loop.parallel_accesses`` metadata that refers to that loop, then the ``llvm.access.group`` metadata that each refer to one of the access
groups of a loop's ``llvm.loop.parallel_accesses`` metadata, then the
loop has no loop carried memory dependences and is considered to be a loop has no loop carried memory dependences and is considered to be a
parallel loop. parallel loop.
Note that if not all memory access instructions belong to an access Note that if not all memory access instructions belong to an access
group referred to by ``llvm.loop.parallel_accesses``, then the loop must group referred to by ``llvm.loop.parallel_accesses``, then the loop must
not be considered trivially parallel. Additional not be considered trivially parallel. Additional
memory dependence analysis is required to make that determination. As a fail memory dependence analysis is required to make that determination. As a fail
safe mechanism, this causes loops that were originally parallel to be considered safe mechanism, this causes loops that were originally parallel to be considered
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