[llvm] r264383 - StringMap: reserve appropriate size when initializing from an initializer list

[Mehdi Amini via llvm-commits]

Hi Don,

You may want to look at the series of changes I committed to StringMap and DenseMap.

The StringMapImpl constructor looks like this now:

StringMapImpl::StringMapImpl(unsigned InitSize, unsigned itemSize) {
  ItemSize = itemSize;
  
  // If a size is specified, initialize the table with that many buckets.
  if (InitSize) {
    // The table will grow when the number of entries reach 3/4 of the number of
    // buckets. To guarantee that "InitSize" number of entries can be inserted
    // in the table without growing, we allocate just what is needed here.
    init(getMinBucketToReserveForEntries(InitSize));
    return;
  }

I hope this address your concern.

-- 
Mehdi


> On Mar 25, 2016, at 7:39 AM, don hinton <hintonda at gmail.com> wrote:
> 
> Won't this still force a rehash since the table will be more that 3/4 full?  Assuming the initialization list contains unique keys.
> 
> On Mar 25, 2016 10:11 AM, "David Blaikie via llvm-commits" <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Worth a test?
> 
> On Mar 24, 2016 11:02 PM, "Mehdi Amini via llvm-commits" <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: mehdi_amini
> Date: Fri Mar 25 00:57:47 2016
> New Revision: 264383
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=264383&view=rev <http://llvm.org/viewvc/llvm-project?rev=264383&view=rev>
> Log:
> StringMap: reserve appropriate size when initializing from an initializer list
> 
> From: Mehdi Amini <mehdi.amini at apple.com <mailto:mehdi.amini at apple.com>>
> 
> Modified:
>     llvm/trunk/include/llvm/ADT/StringMap.h
> 
> Modified: llvm/trunk/include/llvm/ADT/StringMap.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringMap.h?rev=264383&r1=264382&r2=264383&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringMap.h?rev=264383&r1=264382&r2=264383&view=diff>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/StringMap.h (original)
> +++ llvm/trunk/include/llvm/ADT/StringMap.h Fri Mar 25 00:57:47 2016
> @@ -233,7 +233,7 @@ public:
>        Allocator(A) {}
> 
>    StringMap(std::initializer_list<std::pair<StringRef, ValueTy>> List)
> -      : StringMapImpl(static_cast<unsigned>(sizeof(MapEntryTy))) {
> +      : StringMapImpl(List.size(), static_cast<unsigned>(sizeof(MapEntryTy))) {
>      for (const auto &P : List) {
>        insert(P);
>      }
> 
> 
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