Author: rsmith
Date: Wed Feb 17 15:52:44 2016
New Revision: 261161
URL: http://llvm.org/viewvc/llvm-project?rev=261161&view=rev
Log:
[modules] Cache 'acceptable decl' lookups for namespaces. In projects with
thousands of modules, each of which declares the same namespace, linearly
scanning the redecl chain looking for a visible declaration (once for each leaf
module, for each use) performs very poorly. Namespace visibility can only
decrease when we leave a module during a module build step, and we never care
*which* visible declaration of a namespace we find, so we can cache this very
effectively.
This results in a 35x speedup on one of our internal build steps (2m -> 3.5s),
but is hard to unit test because it requires a very large number of modules.
Ideas for a test appreciated! No functionality change intended other than the
speedup.
Modified:
cfe/trunk/include/clang/Sema/Sema.h
cfe/trunk/lib/Sema/SemaDecl.cpp
cfe/trunk/lib/Sema/SemaLookup.cpp
Modified: cfe/trunk/include/clang/Sema/Sema.h
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Sema/Sema.h?rev=261161&r1=261160&r2=261161&view=diff
==============================================================================
--- cfe/trunk/include/clang/Sema/Sema.h (original)
+++ cfe/trunk/include/clang/Sema/Sema.h Wed Feb 17 15:52:44 2016
@@ -6617,6 +6617,10 @@ public:
/// template defined within it.
llvm::DenseSet<Module*> &getLookupModules();
+ /// \brief Map from the most recent declaration of a namespace to the most
+ /// recent visible declaration of that namespace.
+ llvm::DenseMap<NamedDecl*, NamedDecl*> VisibleNamespaceCache;
+
/// \brief Whether we are in a SFINAE context that is not associated with
/// template instantiation.
///
Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=261161&r1=261160&r2=261161&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDecl.cpp Wed Feb 17 15:52:44 2016
@@ -14826,6 +14826,9 @@ void Sema::ActOnModuleEnd(SourceLocation
VisibleModules = std::move(VisibleModulesStack.back());
VisibleModulesStack.pop_back();
VisibleModules.setVisible(Mod, DirectiveLoc);
+ // Leaving a module hides namespace names, so our visible namespace cache
+ // is now out of date.
+ VisibleNamespaceCache.clear();
}
}
Modified: cfe/trunk/lib/Sema/SemaLookup.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaLookup.cpp?rev=261161&r1=261160&r2=261161&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaLookup.cpp (original)
+++ cfe/trunk/lib/Sema/SemaLookup.cpp Wed Feb 17 15:52:44 2016
@@ -1566,6 +1566,10 @@ static NamedDecl *findAcceptableDecl(Sem
assert(!LookupResult::isVisible(SemaRef, D) && "not in slow case");
for (auto RD : D->redecls()) {
+ // Don't bother with extra checks if we already know this one isn't
visible.
+ if (RD == D)
+ continue;
+
if (auto ND = dyn_cast<NamedDecl>(RD)) {
// FIXME: This is wrong in the case where the previous declaration is not
// visible in the same scope as D. This needs to be done much more
@@ -1579,6 +1583,23 @@ static NamedDecl *findAcceptableDecl(Sem
}
NamedDecl *LookupResult::getAcceptableDeclSlow(NamedDecl *D) const {
+ if (auto *ND = dyn_cast<NamespaceDecl>(D)) {
+ // Namespaces are a bit of a special case: we expect there to be a lot of
+ // redeclarations of some namespaces, all declarations of a namespace are
+ // essentially interchangeable, all declarations are found by name lookup
+ // if any is, and namespaces are never looked up during template
+ // instantiation. So we benefit from caching the check in this case, and
+ // it is correct to do so.
+ auto *Key = ND->getCanonicalDecl();
+ if (auto *Acceptable = getSema().VisibleNamespaceCache.lookup(Key))
+ return Acceptable;
+ auto *Acceptable =
+ isVisible(getSema(), Key) ? Key : findAcceptableDecl(getSema(), Key);
+ if (Acceptable)
+ getSema().VisibleNamespaceCache.insert(std::make_pair(Key, Acceptable));
+ return Acceptable;
+ }
+
return findAcceptableDecl(getSema(), D);
}
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