[llvm] [clang] [AArch64] Support optional constant offset for constraint "S" (PR #80255)

[Peter Smith via cfe-commits]

smithp35 wrote:

Just to make sure I've understood:
* x86_64's support for constraint "s" was hoisted into the target independent TargetLowering in https://reviews.llvm.org/D61560 
* Clang's implementation of constraint "s" isn't restricted to non-PIC/non-PIE like GCC's
* We can implement constraint "S" in terms of constraint "s" as Clang's implementation of "s" is equivalent to AArch64 "S".

On that basis this looks reasonable to me. I've not had time to pick over the details of the code/test changes though.

https://github.com/llvm/llvm-project/pull/80255