[AArch64] Attempt to sink mul operands

Authored by NickGuy on Dec 2 2020, 7:16 AM.


[AArch64] Attempt to sink mul operands

Following on from D91255, this patch is responsible for sinking relevant mul
operands to the same block so that umull/smull instructions can be correctly
generated by the mul combine implemented in the aforementioned patch.

Differential revision: https://reviews.llvm.org/D91271