[llvm] r230866 - IndexedMap: Default to SmallVector<T, 0>

[Philip Reames]

Can you add a comment explaining why this matters?  From the code, it's 
not clear why the SmallVector<T, 0> trick is needed.  (Or what it's 
doing for that matter.)


On 02/28/2015 12:15 PM, Benjamin Kramer wrote:
> Author: d0k
> Date: Sat Feb 28 14:15:07 2015
> New Revision: 230866
>
> URL: http://llvm.org/viewvc/llvm-project?rev=230866&view=rev
> Log:
> IndexedMap: Default to SmallVector<T, 0>
>
> This looks ridiculous but SmallVector's realloc tricks really help with
> large vectors of PODs, such as our virtreg IndexedMap.
>
> Modified:
>      llvm/trunk/include/llvm/ADT/IndexedMap.h
>
> Modified: llvm/trunk/include/llvm/ADT/IndexedMap.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/IndexedMap.h?rev=230866&r1=230865&r2=230866&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/IndexedMap.h (original)
> +++ llvm/trunk/include/llvm/ADT/IndexedMap.h Sat Feb 28 14:15:07 2015
> @@ -21,16 +21,16 @@
>   #define LLVM_ADT_INDEXEDMAP_H
>   
>   #include "llvm/ADT/STLExtras.h"
> +#include "llvm/ADT/SmallVector.h"
>   #include <cassert>
>   #include <functional>
> -#include <vector>
>   
>   namespace llvm {
>   
>   template <typename T, typename ToIndexT = llvm::identity<unsigned> >
>     class IndexedMap {
>       typedef typename ToIndexT::argument_type IndexT;
> -    typedef std::vector<T> StorageT;
> +    typedef SmallVector<T, 0> StorageT;
>       StorageT storage_;
>       T nullVal_;
>       ToIndexT toIndex_;
>
>
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