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

1 files changed, 1 insertions, 3 deletions

diff --git a/test/CodeGen/X86/inline-asm-sp-clobber-memcpy.ll b/test/CodeGen/X86/inline-asm-sp-clobber-memcpy.ll
index f64ccb8468..b55571bcba 100644
--- a/test/CodeGen/X86/inline-asm-sp-clobber-memcpy.ll
+++ b/test/CodeGen/X86/inline-asm-sp-clobber-memcpy.ll
@@ -13,7 +13,5 @@ define void @test1(%struct.foo* nocapture %x, i32 %y, i8* %z) nounwind {
 
 ; CHECK-LABEL: test1:
 ; CHECK: movl %esp, %esi
-; CHECK: movl %esi, %edx
-; CHECK: rep;movsl
-; CHECK: movl %edx, %esi
+; CHECK-NOT: rep;movsl
 }