[llvm] r292420 - [ThinLTO] Add a recursive step in Metadata lazy-loading

[Mehdi Amini via llvm-commits]

r292505.


> On Jan 19, 2017, at 10:48 AM, Hans Wennborg <hans at chromium.org> wrote:
> 
> Sounds good to me. Mehdi, go ahead and merge or let me know if you'd
> like me to do it.
> 
> Thanks,
> Hans
> 
> On Wed, Jan 18, 2017 at 12:19 PM, Peter Collingbourne <peter at pcc.me.uk> wrote:
>> Approved.
>> 
>> Peter
>> 
>> On Wed, Jan 18, 2017 at 10:51 AM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>>> 
>>> Hi Peter,
>>> 
>>> I’d like to cherry-pick this into the 4.0 release. This is a follow-up to
>>> r291027, it achieve what was originally promised.
>>> 
>>> It will only affect ThinLTO, as lazy-loading happens only there.
>>> 
>>> Thanks,
>>> 
>>> —
>>> Mehdi
>>> 
>>>> On Jan 18, 2017, at 10:36 AM, Mehdi Amini via llvm-commits
>>>> <llvm-commits at lists.llvm.org> wrote:
>>>> 
>>>> Author: mehdi_amini
>>>> Date: Wed Jan 18 12:36:21 2017
>>>> New Revision: 292420
>>>> 
>>>> URL: http://llvm.org/viewvc/llvm-project?rev=292420&view=rev
>>>> Log:
>>>> [ThinLTO] Add a recursive step in Metadata lazy-loading
>>>> 
>>>> Summary:
>>>> Without this, we're stressing the RAUW of unique nodes,
>>>> which is a costly operation. This is intended to limit
>>>> the number of RAUW, and is very effective on the total
>>>> link-time of opt with ThinLTO, before:
>>>> 
>>>> real 4m4.587s  user 15m3.401s  sys 0m23.616s
>>>> 
>>>> after:
>>>> 
>>>> real 3m25.261s user 12m22.132s sys 0m24.152s
>>>> 
>>>> Reviewers: tejohnson, pcc
>>>> 
>>>> Subscribers: llvm-commits
>>>> 
>>>> Differential Revision: https://reviews.llvm.org/D28751
>>>> 
>>>> Modified:
>>>>   llvm/trunk/lib/Bitcode/Reader/MetadataLoader.cpp
>>>>   llvm/trunk/test/ThinLTO/X86/lazyload_metadata.ll
>>>> 
>>>> Modified: llvm/trunk/lib/Bitcode/Reader/MetadataLoader.cpp
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Bitcode/Reader/MetadataLoader.cpp?rev=292420&r1=292419&r2=292420&view=diff
>>>> 
>>>> ==============================================================================
>>>> --- llvm/trunk/lib/Bitcode/Reader/MetadataLoader.cpp (original)
>>>> +++ llvm/trunk/lib/Bitcode/Reader/MetadataLoader.cpp Wed Jan 18 12:36:21
>>>> 2017
>>>> @@ -768,13 +768,12 @@ void MetadataLoader::MetadataLoaderImpl:
>>>>    unsigned ID, PlaceholderQueue &Placeholders) {
>>>>  assert(ID < (MDStringRef.size()) + GlobalMetadataBitPosIndex.size());
>>>>  assert(ID >= MDStringRef.size() && "Unexpected lazy-loading of
>>>> MDString");
>>>> -#ifndef NDEBUG
>>>>  // Lookup first if the metadata hasn't already been loaded.
>>>>  if (auto *MD = MetadataList.lookup(ID)) {
>>>>    auto *N = dyn_cast_or_null<MDNode>(MD);
>>>> -    assert(N && N->isTemporary() && "Lazy loading an already loaded
>>>> metadata");
>>>> +    if (!N->isTemporary())
>>>> +      return;
>>>>  }
>>>> -#endif
>>>>  SmallVector<uint64_t, 64> Record;
>>>>  StringRef Blob;
>>>>  IndexCursor.JumpToBit(GlobalMetadataBitPosIndex[ID -
>>>> MDStringRef.size()]);
>>>> @@ -827,8 +826,22 @@ Error MetadataLoader::MetadataLoaderImpl
>>>>  auto getMD = [&](unsigned ID) -> Metadata * {
>>>>    if (ID < MDStringRef.size())
>>>>      return lazyLoadOneMDString(ID);
>>>> -    if (!IsDistinct)
>>>> +    if (!IsDistinct) {
>>>> +      if (auto *MD = MetadataList.lookup(ID))
>>>> +        return MD;
>>>> +      // If lazy-loading is enabled, we try recursively to load the
>>>> operand
>>>> +      // instead of creating a temporary.
>>>> +      if (ID < (MDStringRef.size() + GlobalMetadataBitPosIndex.size()))
>>>> {
>>>> +        // Create a temporary for the node that is referencing the
>>>> operand we
>>>> +        // will lazy-load. It is needed before recursing in case there
>>>> are
>>>> +        // uniquing cycles.
>>>> +        MetadataList.getMetadataFwdRef(NextMetadataNo);
>>>> +        lazyLoadOneMetadata(ID, Placeholders);
>>>> +        return MetadataList.lookup(ID);
>>>> +      }
>>>> +      // Return a temporary.
>>>>      return MetadataList.getMetadataFwdRef(ID);
>>>> +    }
>>>>    if (auto *MD = MetadataList.getMetadataIfResolved(ID))
>>>>      return MD;
>>>>    return &Placeholders.getPlaceholderOp(ID);
>>>> 
>>>> Modified: llvm/trunk/test/ThinLTO/X86/lazyload_metadata.ll
>>>> URL:
>>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/ThinLTO/X86/lazyload_metadata.ll?rev=292420&r1=292419&r2=292420&view=diff
>>>> 
>>>> ==============================================================================
>>>> --- llvm/trunk/test/ThinLTO/X86/lazyload_metadata.ll (original)
>>>> +++ llvm/trunk/test/ThinLTO/X86/lazyload_metadata.ll Wed Jan 18 12:36:21
>>>> 2017
>>>> @@ -17,7 +17,7 @@
>>>> ; RUN:          -o /dev/null -disable-ondemand-mds-loading -stats \
>>>> ; RUN:  2>&1 | FileCheck %s -check-prefix=NOTLAZY
>>>> ; NOTLAZY: 58 bitcode-reader  - Number of Metadata records loaded
>>>> -; NOTLAZY: 8 bitcode-reader  - Number of MDStrings loaded
>>>> +; NOTLAZY: 6 bitcode-reader  - Number of MDStrings loaded
>>>> 
>>>> 
>>>> target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
>>>> @@ -48,7 +48,7 @@ define void @globalfunc3(i32 %arg) {
>>>> !3 = !{!"3"}
>>>> !4 = !{!"4"}
>>>> !5 = !{!"5"}
>>>> -!6 = !{!"6"}
>>>> +!6 = !{!9}
>>>> !7 = !{!"7"}
>>>> !8 = !{!"8"}
>>>> -!9 = !{!"9"}
>>>> +!9 = !{!6}
>>>> 
>>>> 
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>>> 
>> 
>> 
>> 
>> --
>> --
>> Peter