[NFC] Reducing allocations in AST attributes

[kevgs]

Summary

In my test case max resident memory changed from 65760k to 64476k which is 1.9% improvement.

Allocations in grow_pod changed from 8847 to 4872 according to tcmalloc heap profiler.

Overall running time remained the same.

[kevgs]

My test case is:

clang++ -std=c++14 -fsyntax-only test.cc

#include <algorithm>
#include <iostream>
#include <vector>
int main() {

std::vector<int> v = {1, 2, 3};
std::for_each(v.begin(), v.end(), [](auto i) { std::cout << i; });
return 0;

}

[kevgs]

Btw, ConstAttrVec is never used.

[majnemer]

LGTM

include/clang/AST/AttrIterator.h

42

Might as well clang-format this line.

43

I'd delete this.

[kevgs]

clang-formatted + dead code removed

[kevgs]

I have no commit rights.

[aaron.ballman]

Thank you! I've commit in r278812.

include/clang/AST/AttrIterator.h

 // warnings if a matching delete overload is not declared, even though the
 // throw() spec guarantees it will not be implicitly called.
 void operator delete(void *Ptr, const clang::ASTContext &C, size_t);
 void operator delete[](void *Ptr, const clang::ASTContext &C, size_t);
 
 namespace clang {
 
 /// AttrVec - A vector of Attr, which is how they are stored on the AST.
-typedef SmallVector<Attr*, 2> AttrVec;
-typedef SmallVector<const Attr*, 2> ConstAttrVec;
+typedef SmallVector<Attr *, 4> AttrVec;
 
 /// specific_attr_iterator - Iterates over a subrange of an AttrVec, only
 /// providing attributes that are of a specific type.
 template <typename SpecificAttr, typename Container = AttrVec>
 class specific_attr_iterator {
   typedef typename Container::const_iterator Iterator;
 
   /// Current - The current, underlying iterator.
   /// In order to ensure we don't dereference an invalid iterator unless