r228234 - [modules] When using -E, we may try to merge decls despite having no Sema
Richard Smith
richard at metafoo.co.uk
Mon Mar 23 16:18:06 PDT 2015
On Mon, Mar 23, 2015 at 3:59 PM, Ben Langmuir <blangmuir at apple.com> wrote:
>
> On Mar 23, 2015, at 3:43 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>
> On Mon, Mar 23, 2015 at 2:41 PM, Ben Langmuir <blangmuir at apple.com> wrote:
>
>>
>> On Mar 23, 2015, at 1:05 PM, Richard Smith <richard at metafoo.co.uk> wrote:
>>
>> On Sat, Mar 14, 2015 at 9:25 AM, Ben Langmuir <blangmuir at apple.com>
>> wrote:
>>
>>> Hi Richard,
>>>
>>> This commit looks like it caused a regression in PCH-loading performance
>>> when the PCH imports modules. It doesn’t affect performance of loading
>>> modules on their own, or of a PCH that doesn’t use modules. If you have
>>> access to a Darwin system, it’s easy to reproduce with:
>>>
>>> $ cat t.h
>>> @import Cocoa;
>>>
>>> $ cat t.m
>>> // empty
>>>
>>> $ clang -fmodules -fmodules-cache-path=mcp -x objective-c-header t.h -o
>>> t.pch
>>> $ time clang -fmodules -fmodules-cache-path=mcp -Xclang -include-pch
>>> -Xclang t.pch t.m -fsyntax-only
>>>
>>> I’m seeing ~8x difference between r228233 and r228234. In real world
>>> code (where the .m file isn’t empty) we’ve seen up to a ~90% difference.
>>>
>>> Do you know what’s going on here?
>>
>>
>> Hmm. I suspect this change causes the lookup table for the translation
>> unit to be built, which in turn pulls in all the lexical contents of the
>> translation unit (because outside of C++ we don't serialize a DeclContext
>> lookup table for the TU, nor even build one usually).
>>
>> When a PCH loads I think we do it without Sema, but (at least previously)
>>> queued up the interesting Decls we saw for when Sema was added later. So
>>> I’m surprised this had such a big effect.
>>
>>
>> If we were loading PCHs without Sema, then I think before this change we
>> would not have merged declarations of the same entity from two independent
>> modules imported into the same PCH.
>>
>>
>> Wouldn’t that happen in InitializeSema() when we
>> called pushExternalDeclIntoScope() on the contents of PreloadedDeclIDs?
>>
>
> No; we're talking about the case where a Decl is deserialized before we
> have a Sema instance. If we never deserialized the Decl from its DeclID
> before we had a Sema (which I think is what you're suggesting) we'd never
> have reached the modified code.
>
>
> If we want to support loading Decls without Sema, we need to be able to
> merge them without Sema. If we don't, then we should find whichever
> codepath is leading us to do so and fix it. Being able to load a serialized
> AST without a Sema seems useful to me, in the absence of a good reason why
> it shouldn't work.
>
>
> I thought PCH intentionally wouldn’t deserialize decls until after we
> initialized Sema. Maybe we have a bug (which wouldn’t surprise me), or
> maybe that wasn’t the intent (which would scare me a bit since then we have
> some decls showing up immediately and some waiting for sema with no clear
> split between them).
>
> Perhaps we should use a separate side-table for merging in this case
>> outside C++, rather than falling back to DeclContext lookup?
>>
>>
>> I don’t know this code path well enough to say. What would go into the
>> table (or perhaps more importantly what wouldn’t)?
>>
>
> Any deserialized declarations that should be visible by name lookup in the
> TU would be in the table. The only difference would be that we'd be more
> careful to ensure that we never trigger the import of all lexical
> declarations in the TU in order to build the table.
>
> Are you still seeing this performance problem with Clang trunk? Towards
> the end of last week I fixed a bug where we would unnecessarily pull in all
> lexical declarations within the TU when doing certain lookups, which might
> have fixed this slowdown. (If not, it'd be useful to find out whether
> that's the problem, and if so, what is causing us to load these
> declarations.)
>
>
> Cool, I’ll give ToT a shot. I last tried with r232229.
>
r232928 onwards, or a revision in [232793, 232905), have the change I'm
referring to.
> Ben
>>>
>>> > On Feb 4, 2015, at 3:37 PM, Richard Smith <richard-llvm at metafoo.co.uk>
>>> wrote:
>>> >
>>> > Author: rsmith
>>> > Date: Wed Feb 4 17:37:59 2015
>>> > New Revision: 228234
>>> >
>>> > URL: http://llvm.org/viewvc/llvm-project?rev=228234&view=rev
>>> > Log:
>>> > [modules] When using -E, we may try to merge decls despite having no
>>> Sema
>>> > object. In such a case, use the TU's DC for merging global decls
>>> rather than
>>> > giving up when we find there is no TU scope.
>>> >
>>> > Ultimately, we should probably avoid all loading of decls when
>>> preprocessing,
>>> > but there are other reasonable use cases for loading an AST file with
>>> no Sema
>>> > object for which this is the right thing.
>>> >
>>> > Added:
>>> > cfe/trunk/test/Modules/Inputs/preprocess/
>>> > cfe/trunk/test/Modules/Inputs/preprocess/file.h
>>> > cfe/trunk/test/Modules/Inputs/preprocess/fwd.h
>>> > cfe/trunk/test/Modules/Inputs/preprocess/module.modulemap
>>> > Modified:
>>> > cfe/trunk/include/clang/Frontend/CompilerInstance.h
>>> > cfe/trunk/lib/Frontend/CompilerInstance.cpp
>>> > cfe/trunk/lib/Serialization/ASTReaderDecl.cpp
>>> > cfe/trunk/test/Modules/preprocess.m
>>> >
>>> > Modified: cfe/trunk/include/clang/Frontend/CompilerInstance.h
>>> > URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Frontend/CompilerInstance.h?rev=228234&r1=228233&r2=228234&view=diff
>>> >
>>> ==============================================================================
>>> > --- cfe/trunk/include/clang/Frontend/CompilerInstance.h (original)
>>> > +++ cfe/trunk/include/clang/Frontend/CompilerInstance.h Wed Feb 4
>>> 17:37:59 2015
>>> > @@ -588,7 +588,7 @@ public:
>>> > /// Create an external AST source to read a PCH file.
>>> > ///
>>> > /// \return - The new object on success, or null on failure.
>>> > - static ExternalASTSource *createPCHExternalASTSource(
>>> > + static IntrusiveRefCntPtr<ASTReader> createPCHExternalASTSource(
>>> > StringRef Path, const std::string &Sysroot, bool
>>> DisablePCHValidation,
>>> > bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext
>>> &Context,
>>> > void *DeserializationListener, bool OwnDeserializationListener,
>>> >
>>> > Modified: cfe/trunk/lib/Frontend/CompilerInstance.cpp
>>> > URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Frontend/CompilerInstance.cpp?rev=228234&r1=228233&r2=228234&view=diff
>>> >
>>> ==============================================================================
>>> > --- cfe/trunk/lib/Frontend/CompilerInstance.cpp (original)
>>> > +++ cfe/trunk/lib/Frontend/CompilerInstance.cpp Wed Feb 4 17:37:59
>>> 2015
>>> > @@ -388,32 +388,30 @@ void CompilerInstance::createASTContext(
>>> > void CompilerInstance::createPCHExternalASTSource(
>>> > StringRef Path, bool DisablePCHValidation, bool
>>> AllowPCHWithCompilerErrors,
>>> > void *DeserializationListener, bool OwnDeserializationListener) {
>>> > - IntrusiveRefCntPtr<ExternalASTSource> Source;
>>> > bool Preamble = getPreprocessorOpts().PrecompiledPreambleBytes.first
>>> != 0;
>>> > - Source = createPCHExternalASTSource(
>>> > + ModuleManager = createPCHExternalASTSource(
>>> > Path, getHeaderSearchOpts().Sysroot, DisablePCHValidation,
>>> > AllowPCHWithCompilerErrors, getPreprocessor(), getASTContext(),
>>> > DeserializationListener, OwnDeserializationListener, Preamble,
>>> > getFrontendOpts().UseGlobalModuleIndex);
>>> > - ModuleManager = static_cast<ASTReader*>(Source.get());
>>> > - getASTContext().setExternalSource(Source);
>>> > }
>>> >
>>> > -ExternalASTSource *CompilerInstance::createPCHExternalASTSource(
>>> > +IntrusiveRefCntPtr<ASTReader>
>>> CompilerInstance::createPCHExternalASTSource(
>>> > StringRef Path, const std::string &Sysroot, bool
>>> DisablePCHValidation,
>>> > bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext
>>> &Context,
>>> > void *DeserializationListener, bool OwnDeserializationListener,
>>> > bool Preamble, bool UseGlobalModuleIndex) {
>>> > HeaderSearchOptions &HSOpts =
>>> PP.getHeaderSearchInfo().getHeaderSearchOpts();
>>> >
>>> > - std::unique_ptr<ASTReader> Reader;
>>> > - Reader.reset(new ASTReader(PP, Context,
>>> > - Sysroot.empty() ? "" : Sysroot.c_str(),
>>> > - DisablePCHValidation,
>>> > - AllowPCHWithCompilerErrors,
>>> > - /*AllowConfigurationMismatch*/false,
>>> > - HSOpts.ModulesValidateSystemHeaders,
>>> > - UseGlobalModuleIndex));
>>> > + IntrusiveRefCntPtr<ASTReader> Reader(
>>> > + new ASTReader(PP, Context, Sysroot.empty() ? "" :
>>> Sysroot.c_str(),
>>> > + DisablePCHValidation, AllowPCHWithCompilerErrors,
>>> > + /*AllowConfigurationMismatch*/ false,
>>> > + HSOpts.ModulesValidateSystemHeaders,
>>> UseGlobalModuleIndex));
>>> > +
>>> > + // We need the external source to be set up before we read the AST,
>>> because
>>> > + // eagerly-deserialized declarations may use it.
>>> > + Context.setExternalSource(Reader.get());
>>> >
>>> > Reader->setDeserializationListener(
>>> > static_cast<ASTDeserializationListener
>>> *>(DeserializationListener),
>>> > @@ -427,7 +425,7 @@ ExternalASTSource *CompilerInstance::cre
>>> > // Set the predefines buffer as suggested by the PCH reader.
>>> Typically, the
>>> > // predefines buffer will be empty.
>>> > PP.setPredefines(Reader->getSuggestedPredefines());
>>> > - return Reader.release();
>>> > + return Reader;
>>> >
>>> > case ASTReader::Failure:
>>> > // Unrecoverable failure: don't even try to process the input file.
>>> > @@ -442,6 +440,7 @@ ExternalASTSource *CompilerInstance::cre
>>> > break;
>>> > }
>>> >
>>> > + Context.setExternalSource(nullptr);
>>> > return nullptr;
>>> > }
>>> >
>>> >
>>> > Modified: cfe/trunk/lib/Serialization/ASTReaderDecl.cpp
>>> > URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Serialization/ASTReaderDecl.cpp?rev=228234&r1=228233&r2=228234&view=diff
>>> >
>>> ==============================================================================
>>> > --- cfe/trunk/lib/Serialization/ASTReaderDecl.cpp (original)
>>> > +++ cfe/trunk/lib/Serialization/ASTReaderDecl.cpp Wed Feb 4 17:37:59
>>> 2015
>>> > @@ -2591,6 +2591,11 @@ DeclContext *ASTDeclReader::getPrimaryCo
>>> > return ED->getASTContext().getLangOpts().CPlusPlus?
>>> ED->getDefinition()
>>> > : nullptr;
>>> >
>>> > + // We can see the TU here only if we have no Sema object. In that
>>> case,
>>> > + // there's no TU scope to look in, so using the DC alone is
>>> sufficient.
>>> > + if (auto *TU = dyn_cast<TranslationUnitDecl>(DC))
>>> > + return TU;
>>> > +
>>> > return nullptr;
>>> > }
>>> >
>>> >
>>> > Added: cfe/trunk/test/Modules/Inputs/preprocess/file.h
>>> > URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/Inputs/preprocess/file.h?rev=228234&view=auto
>>> >
>>> ==============================================================================
>>> > --- cfe/trunk/test/Modules/Inputs/preprocess/file.h (added)
>>> > +++ cfe/trunk/test/Modules/Inputs/preprocess/file.h Wed Feb 4
>>> 17:37:59 2015
>>> > @@ -0,0 +1,3 @@
>>> > +struct __FILE;
>>> > +#include "fwd.h"
>>> > +typedef struct __FILE FILE;
>>> >
>>> > Added: cfe/trunk/test/Modules/Inputs/preprocess/fwd.h
>>> > URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/Inputs/preprocess/fwd.h?rev=228234&view=auto
>>> >
>>> ==============================================================================
>>> > --- cfe/trunk/test/Modules/Inputs/preprocess/fwd.h (added)
>>> > +++ cfe/trunk/test/Modules/Inputs/preprocess/fwd.h Wed Feb 4 17:37:59
>>> 2015
>>> > @@ -0,0 +1 @@
>>> > +struct __FILE;
>>> >
>>> > Added: cfe/trunk/test/Modules/Inputs/preprocess/module.modulemap
>>> > URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/Inputs/preprocess/module.modulemap?rev=228234&view=auto
>>> >
>>> ==============================================================================
>>> > --- cfe/trunk/test/Modules/Inputs/preprocess/module.modulemap (added)
>>> > +++ cfe/trunk/test/Modules/Inputs/preprocess/module.modulemap Wed Feb
>>> 4 17:37:59 2015
>>> > @@ -0,0 +1,2 @@
>>> > +module fwd { header "fwd.h" export * }
>>> > +module file { header "file.h" export * }
>>> >
>>> > Modified: cfe/trunk/test/Modules/preprocess.m
>>> > URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Modules/preprocess.m?rev=228234&r1=228233&r2=228234&view=diff
>>> >
>>> ==============================================================================
>>> > --- cfe/trunk/test/Modules/preprocess.m (original)
>>> > +++ cfe/trunk/test/Modules/preprocess.m Wed Feb 4 17:37:59 2015
>>> > @@ -1,9 +1,14 @@
>>> > // RUN: rm -rf %t
>>> > -// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs
>>> -include %S/Inputs/preprocess-prefix.h -E %s | FileCheck -strict-whitespace
>>> %s
>>> > -// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -x
>>> objective-c-header -emit-pch %S/Inputs/preprocess-prefix.h -o %t.pch
>>> > -// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs
>>> -include-pch %t.pch -E %s | FileCheck -strict-whitespace %s
>>> > +// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I
>>> %S/Inputs/preprocess -include %S/Inputs/preprocess-prefix.h -E %s |
>>> FileCheck -strict-whitespace %s
>>> > +// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I
>>> %S/Inputs/preprocess -x objective-c-header -emit-pch
>>> %S/Inputs/preprocess-prefix.h -o %t.pch
>>> > +// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I
>>> %S/Inputs/preprocess -include-pch %t.pch -E %s | FileCheck
>>> -strict-whitespace %s
>>> > +//
>>> > +// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I
>>> %S/Inputs/preprocess -x objective-c++ -include
>>> %S/Inputs/preprocess-prefix.h -E %s | FileCheck -strict-whitespace %s
>>> > +// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I
>>> %S/Inputs/preprocess -x objective-c++-header -emit-pch
>>> %S/Inputs/preprocess-prefix.h -o %t.pch
>>> > +// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I %S/Inputs -I
>>> %S/Inputs/preprocess -x objective-c++ -include-pch %t.pch -E %s | FileCheck
>>> -strict-whitespace %s
>>> > #import "diamond_right.h"
>>> > #import "diamond_right.h" // to check that imports get their own line
>>> > +#include "file.h"
>>> > void test() {
>>> > top_left_before();
>>> > left_and_right();
>>> > @@ -15,6 +20,7 @@ void test() {
>>> >
>>> > // CHECK: @import diamond_right; /* clang -E: implicit import for
>>> "{{.*}}diamond_right.h" */{{$}}
>>> > // CHECK: @import diamond_right; /* clang -E: implicit import for
>>> "{{.*}}diamond_right.h" */{{$}}
>>> > +// CHECK: @import file; /* clang -E: implicit import for
>>> "{{.*}}file.h" */{{$}}
>>> > // CHECK-NEXT: void test() {{{$}}
>>> > // CHECK-NEXT: top_left_before();{{$}}
>>> > // CHECK-NEXT: left_and_right();{{$}}
>>> >
>>> >
>>> > _______________________________________________
>>> > cfe-commits mailing list
>>> > cfe-commits at cs.uiuc.edu
>>> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>>>
>>
>
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