[PATCH] D31123: RegisterPressure: Add operators to RegisterMaskPair

[Daniel Berlin via llvm-commits]

On Sun, Mar 19, 2017 at 3:28 PM, Axel Davy <axel.davy at ens.fr> wrote:

> I'm not familiar with std::transform, but it looks like one element in the
> source
> can only give one element in the destination, whereas here you can have
> one element
> decomposing into several ones.
>

std::transform does not require the input == the output type.

It only requires that assignment of the output iterator takes the type

Thus, the following should work:

std::transform(Regs.begin(), Regs.end(), vector_inserter(Result), [&]
(const RegisterMaskPair &RegPair)
{

> return getPairsForReg(RegPair.RegUnit,  RegPair.LaneMask)

});


Where vector_inserter is defined as:
class vector__inserter
    : public std::iterator<std::output_iterator_tag, void, void, void,
void> {
private:
  SmallVectorImpl<RegisterMaskPair> &Result;

public:
  explicit op_inserter(SmallVectorImpl<RegisterMaskPair> &Result) :
Result(Result) {}

  op_inserter &operator=(const SmallVectorImpl<RegisterMaskPair> &Val) {
    Result.insert(Result.end(), Val.begin(), Val.end())
    return *this;
  }
  vector_inserter &operator*() { return *this; }
  vector_inserter &operator++() { return *this; }
  vector_inserter &operator++(int) { return *this; }
};
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