[llvm] [AggressiveInstCombine] Merge consecutive loads of mixed sizes (PR #129263)

[Zhenyang Xu via llvm-commits]

Cancelll wrote:

It seems like this potential change was mentioned when the transformation was first proposed.
https://reviews.llvm.org/D127392
>>In [D127392#3807970](https://reviews.llvm.org/D127392#3807970), [@nikic](https://reviews.llvm.org/p/nikic/) wrote:
>From a cursory look it looks fine, I assume [@dmgreen](https://reviews.llvm.org/p/dmgreen/) has reviewed in detail :)
I have one note (that can be addressed later): There's currently a check that the loads have the same size. Does that mean that if you have a partially folded pattern (e.g. one i16 load plus two i8 loads) that it will not get folded? If so, this seems like something we should relax (later).

>[bipmis](https://reviews.llvm.org/p/bipmis/): Thats correct. Currently we are folding loads of same size only in a chain. So for above case if two i8 loads belong to single lower chain they can be folded.
Agreed. This is more to do with a stricter basic implementation first. We can relax this later.

https://github.com/llvm/llvm-project/pull/129263