llvm dev - Oct 2017 - Expose aliasing information in getModRefInfo (or viceversa?)

Hi,

This came up in https://reviews.llvm.org/D38569, and I'd like some input on
what's the best way to get alias and mod-ref info without having two alias
calls.

A couple of ideas:
(a) Extend the getModRefInfo interface (+getModRefBehavior,
+gerArgModRefInfo) to return a pair {ModRefInfo, AliasResult}.

The AliasResult can be optional based on an argument
     e.g.:
    struct MRI_AR { ModRefInfo MRI, AliasResult AR };
    MRI_AR getModRefInfoAlias (LoadInst *LI, MemoryLocation Loc, bool
SetAliasResultField);

Add wrapper APIs to preserve current calls.
    e.g.:
     ModRefInfo getModRefInfo (LoadInst *LI, MemoryLocation Loc) {
          return getModRefInfoAlias (LI, Loc, false).MRI;
      }

(b) From talking offline with George, introducing a MRI_MustMod in
ModRefInfo.


Open question: How to handle callsites.


In terms of whether this is worth doing, as a preliminary timing test I
timed the llvm bootstrap build with 1 vs 2 alias calls in D38569:
instructionClobbersQuery:296, and got the following:
2 alias calls:
real    62m52.627s
user    2769m46.964s
sys     17m48.072s
1 alias call:
real    62m56.659s
user    2766m40.452s
sys     17m46.312s

Thoughts?


Thanks,
Alina
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FWIW:  Bootstrap is probably not a good test of this, there are bugs filed
where we end up with tons of loads and stores to test against each other.
That's actually fairly rare in bootstrap, as you can see.
Let me get you some test cases.

My guess is that we should go with mustmod.


As for callsites, adding mustmod works for call, memloc and call, call
testing.


On Mon, Oct 9, 2017, 4:48 PM Alina Sbirlea <alina.sbirlea at gmail.com>
wrote:
> Hi,
>
> This came up in https://reviews.llvm.org/D38569, and I'd like some
input
> on what's the best way to get alias and mod-ref info without having two
> alias calls.
>
> A couple of ideas:
> (a) Extend the getModRefInfo interface (+getModRefBehavior,
> +gerArgModRefInfo) to return a pair {ModRefInfo, AliasResult}.
>
> The AliasResult can be optional based on an argument
>      e.g.:
>     struct MRI_AR { ModRefInfo MRI, AliasResult AR };
>     MRI_AR getModRefInfoAlias (LoadInst *LI, MemoryLocation Loc, bool
> SetAliasResultField);
>
> Add wrapper APIs to preserve current calls.
>     e.g.:
>      ModRefInfo getModRefInfo (LoadInst *LI, MemoryLocation Loc) {
>           return getModRefInfoAlias (LI, Loc, false).MRI;
>       }
>
> (b) From talking offline with George, introducing a MRI_MustMod in
> ModRefInfo.
>
>
> Open question: How to handle callsites.
>
>
> In terms of whether this is worth doing, as a preliminary timing test I
> timed the llvm bootstrap build with 1 vs 2 alias calls in D38569:
> instructionClobbersQuery:296, and got the following:
> 2 alias calls:
> real    62m52.627s
> user    2769m46.964s
> sys     17m48.072s
> 1 alias call:
> real    62m56.659s
> user    2766m40.452s
> sys     17m46.312s
>
> Thoughts?
>
>
> Thanks,
> Alina
>
>
>
>
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On Mon, Oct 9, 2017 at 1:57 PM, Daniel Berlin <dberlin at dberlin.org>
wrote:
> FWIW:  Bootstrap is probably not a good test of this, there are bugs filed
> where we end up with tons of loads and stores to test against each other.
> That's actually fairly rare in bootstrap, as you can see.
> Let me get you some test cases.
>
SG, thanks!
>
> My guess is that we should go with mustmod.
>
>
> As for callsites, adding mustmod works for call, memloc and call, call
> testing.
>
>
>
> On Mon, Oct 9, 2017, 4:48 PM Alina Sbirlea <alina.sbirlea at
gmail.com>
> wrote:
>
>> Hi,
>>
>> This came up in https://reviews.llvm.org/D38569, and I'd like some
input
>> on what's the best way to get alias and mod-ref info without having
two
>> alias calls.
>>
>> A couple of ideas:
>> (a) Extend the getModRefInfo interface (+getModRefBehavior,
>> +gerArgModRefInfo) to return a pair {ModRefInfo, AliasResult}.
>>
>> The AliasResult can be optional based on an argument
>>      e.g.:
>>     struct MRI_AR { ModRefInfo MRI, AliasResult AR };
>>     MRI_AR getModRefInfoAlias (LoadInst *LI, MemoryLocation Loc, bool
>> SetAliasResultField);
>>
>> Add wrapper APIs to preserve current calls.
>>     e.g.:
>>      ModRefInfo getModRefInfo (LoadInst *LI, MemoryLocation Loc) {
>>           return getModRefInfoAlias (LI, Loc, false).MRI;
>>       }
>>
>> (b) From talking offline with George, introducing a MRI_MustMod in
>> ModRefInfo.
>>
>>
>> Open question: How to handle callsites.
>>
>>
>> In terms of whether this is worth doing, as a preliminary timing test I
>> timed the llvm bootstrap build with 1 vs 2 alias calls in D38569:
>> instructionClobbersQuery:296, and got the following:
>> 2 alias calls:
>> real    62m52.627s
>> user    2769m46.964s
>> sys     17m48.072s
>> 1 alias call:
>> real    62m56.659s
>> user    2766m40.452s
>> sys     17m46.312s
>>
>> Thoughts?
>>
>>
>> Thanks,
>> Alina
>>
>>
>>
>>
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On 10/09/2017 03:57 PM, Daniel Berlin wrote:
> FWIW:  Bootstrap is probably not a good test of this, there are bugs 
> filed where we end up with tons of loads and stores to test against 
> each other.  That's actually fairly rare in bootstrap, as you can see.
> Let me get you some test cases.
>
> My guess is that we should go with mustmod.
I agree.

  -Hal
>
>
> As for callsites, adding mustmod works for call, memloc and call, call 
> testing.
>
>
> On Mon, Oct 9, 2017, 4:48 PM Alina Sbirlea <alina.sbirlea at gmail.com 
> <mailto:alina.sbirlea at gmail.com>> wrote:
>
>     Hi,
>
>     This came up in https://reviews.llvm.org/D38569, and I'd like some
>     input on what's the best way to get alias and mod-ref info without
>     having two alias calls.
>
>     A couple of ideas:
>     (a) Extend the getModRefInfo interface (+getModRefBehavior,
>     +gerArgModRefInfo) to return a pair {ModRefInfo, AliasResult}.
>
>     The AliasResult can be optional based on an argument
>          e.g.:
>         struct MRI_AR { ModRefInfo MRI, AliasResult AR };
>         MRI_AR getModRefInfoAlias (LoadInst *LI, MemoryLocation Loc,
>     bool SetAliasResultField);
>
>     Add wrapper APIs to preserve current calls.
>         e.g.:
>          ModRefInfo getModRefInfo (LoadInst *LI, MemoryLocation Loc) {
>               return getModRefInfoAlias (LI, Loc, false).MRI;
>           }
>
>     (b) From talking offline with George, introducing a MRI_MustMod in
>     ModRefInfo.
>
>
>     Open question: How to handle callsites.
>
>
>     In terms of whether this is worth doing, as a preliminary timing
>     test I timed the llvm bootstrap build with 1 vs 2 alias calls in
>     D38569: instructionClobbersQuery:296, and got the following:
>     2 alias calls:
>     real    62m52.627s
>     user    2769m46.964s
>     sys     17m48.072s
>     1 alias call:
>     real    62m56.659s
>     user    2766m40.452s
>     sys     17m46.312s
>
>     Thoughts?
>
>
>     Thanks,
>     Alina
>
>
>
-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory

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