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Workaround a performance issue with modules + PCH 

More fallout from r228234; when looking up an identifier in a PCH that
imports the Cocoa module on Darwin, it was taking 2 to 5 seconds
because we were hammering the MapVector::erase() function, which is
O(n).  For now, just clear() the contained SmallVector to get back to
0.25 - 0.5 seconds.  This is probably not the long-term fix, because
without modules or without PCH the performance is more like 0.02
seconds.

llvm-svn: 234655
This commit is contained in:
Ben Langmuir 2015-04-10 22:25:42 +00:00
parent b4bf14ceaa
commit eb8bd2d9b3
1 changed files with 4 additions and 1 deletions
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5
clang/lib/Serialization/ASTReader.cpp
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@ -8668,7 +8668,10 @@ void ASTReader::pushExternalDeclIntoScope(NamedDecl *D, DeclarationName Name) {
if (It != PendingFakeLookupResults.end()) {
for (auto *ND : PendingFakeLookupResults[II])
SemaObj->IdResolver.RemoveDecl(ND);
PendingFakeLookupResults.erase(It);
// FIXME: this works around module+PCH performance issue.
// Rather than erase the result from the map, which is O(n), just clear
// the vector of NamedDecls.
It->second.clear();
}
}