Revert "X86 memcpy lowering: use "rep movs" even when esi is used as base pointer" (r204174)
> For functions where esi is used as base pointer, we would previously fall ba
> from lowering memcpy with "rep movs" because that clobbers esi.
>
> With this patch, we just store esi in another physical register, and restore
> it afterwards. This adds a little bit of register preassure, but the more
> efficient memcpy should be worth it.
>
> Differential Revision: http://llvm-reviews.chandlerc.com/D2968
This didn't work. I was ending up with code like this:
lea edi,[esi+38h]
mov ecx,0Fh
mov edx,esi
mov esi,ebx
rep movs dword ptr es:[edi],dword ptr [esi]
lea ecx,[esi+74h] <-- Ooops, we're now using esi before restoring it from edx.
add ebx,3Ch
mov esi,edx
I guess if we want to do this we need stronger glue or something, or doing the expansion
much later.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204829
91177308-0d34-0410-b5e6-
96231b3b80d8