[LV] Don't create partial reductions if factor doesn't match accumulator (#158603)
Check if the scale-factor of the accumulator is the same as the request
ScaleFactor in tryToCreatePartialReductions.
This prevents creating partial reductions if not all instructions in the
reduction chain form partial reductions. e.g. because we do not form a
partial reduction for the loop exit instruction.
Currently code-gen works fine, because the scale factor of
VPPartialReduction is not used during ::execute, but it means we compute
incorrect cost/register pressure, because the partial reduction won't
reduce to the specified scaling factor.
PR: https://github.com/llvm/llvm-project/pull/158603
llvm-project
a7b4dd42 - [LV] Don't create partial reductions if factor doesn't match accumulator (#158603)
