[x86 frame lowering] In 32-bit mode, use ESI as the base pointer.

Previously, we were using EBX, but PIC requires the GOT to be in EBX before 
function calls via PLT GOT pointer.

llvm-svn: 161066
diff --git a/llvm/test/CodeGen/X86/force-align-stack-alloca.ll b/llvm/test/CodeGen/X86/force-align-stack-alloca.ll
index 4ab9067..2ada194 100644
--- a/llvm/test/CodeGen/X86/force-align-stack-alloca.ll
+++ b/llvm/test/CodeGen/X86/force-align-stack-alloca.ll
@@ -24,8 +24,8 @@
 ; CHECK-NEXT: andl   $-32, %esp
 ; CHECK-NEXT: subl   $32, %esp
 ;
-; Now setup the base pointer (%ebx).
-; CHECK-NEXT: movl   %esp, %ebx
+; Now setup the base pointer (%esi).
+; CHECK-NEXT: movl   %esp, %esi
 ; CHECK-NOT:         {{[^ ,]*}}, %esp
 ;
 ; The next adjustment of the stack is due to the alloca.