[PATCH 1/2] [InstCombine] Properly combine metadata when replacing a load with another

[Bjorn Steinbrink]

Hi Hal,

2015-06-23 3:16 GMT+02:00 Hal Finkel <hfinkel at anl.gov>:
> Dropping all AA metadata on these loads when we combine them seems
> quite unfortunate; we should at least be able to keep the AA metadata
> from the original load.

Oops! I had intentionally skipped the AA metadata IDs here because I
wanted the AA metadata to be preserved but forgot that combineMetadata
drops all unknown metadata. Thanks!

> FindAvailableLoadedValue will return the the
> AATags as an optional output parameter. You could then call
> setAAMetadata after you run the combining. Please add a test case for
> this.

Done.

> Also, while you're here, as follow-up, it seems like we should be able
> to pass the AA parameter to FindAvailableLoadedValue too. Should be
> easy to come up with a test: just stick a store to some noalias
> pointer in between the two loads.

Added in a second patch.

Thanks,
Björn

> Thanks again,
> Hal
>
> ----- Original Message -----
>> From: "Björn Steinbrink" <bsteinbr at gmail.com>
>> To: llvm-commits at cs.uiuc.edu
>> Sent: Monday, June 22, 2015 7:56:56 AM
>> Subject: [PATCH] [InstCombine] Properly combine metadata when
>> replacing a     load with another
>>
>>
>> Not doing this can lead to misoptimizations down the line, e.g.
>> because
>> of range metadata on the replacing load excluding values that are
>> valid
>> for the load that is being replaced.
>> ---
>>  .../InstCombine/InstCombineLoadStoreAlloca.cpp        | 12
>>  +++++++++++-
>>  test/Transforms/InstCombine/load-range-metadata.ll    | 19
>>  +++++++++++++++++++
>>  2 files changed, 30 insertions(+), 1 deletion(-)
>>  create mode 100644
>>  test/Transforms/InstCombine/load-range-metadata.ll
>>
>>
>> _______________________________________________
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>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
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