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

[Mehdi Amini via llvm-commits]

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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