[AArch64] Use of isVoid in isLegalAddressingMode API for LSR

All,
I'm in the process of implementing the isLegalAddressingMode API for
AArch64. I noticed that for ARM, the MVT::isVoid is allowed in some
cases.

This was originally committed by Chris here:
http://www.llvm.org/viewvc/llvm-project?view=revision&revision=35601

The commit message comments:
"Allow IV's with scales to be folded into non-store instructions."

I think I understand the general idea, but could someone possibly
elaborated a bit more on what this change is doing? It was only committed
6 years, 10 months ago.. :slight_smile:

It also seems generic; why isn't it in the other backends?

Chad

Ping.