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.

llvm-svn: 204829

1 files changed, 2 insertions, 7 deletions

diff --git a/llvm/test/CodeGen/X86/stack-align-memcpy.ll b/llvm/test/CodeGen/X86/stack-align-memcpy.ll
index d6ea8b31475..0cc3aa84889 100644
--- a/llvm/test/CodeGen/X86/stack-align-memcpy.ll
+++ b/llvm/test/CodeGen/X86/stack-align-memcpy.ll
@@ -15,9 +15,7 @@ define void @test1(%struct.foo* nocapture %x, i32 %y) nounwind {
 ; CHECK-LABEL: test1:
 ; CHECK: andl $-16, %esp
 ; CHECK: movl %esp, %esi
-; CHECK: movl %esi, %edx
-; CHECK: rep;movsl
-; CHECK: movl %edx, %esi
+; CHECK-NOT: rep;movsl
 }
 
 ; PR19012
@@ -30,9 +28,7 @@ define void @test2(%struct.foo* nocapture %x, i32 %y, i8* %z) nounwind {
 
 ; CHECK-LABEL: test2:
 ; CHECK: movl %esp, %esi
-; CHECK: movl %esi, %edx
-; CHECK: rep;movsl
-; CHECK: movl %edx, %esi
+; CHECK-NOT: rep;movsl
 }
 
 ; Check that we do use rep movs if we make the alloca static.
@@ -43,6 +39,5 @@ define void @test3(%struct.foo* nocapture %x, i32 %y, i8* %z) nounwind {
   ret void
 
 ; CHECK-LABEL: test3:
-; CHECK-NOT: movl %esi, %edx
 ; CHECK: rep;movsl
 }