Use LEA to adjust stack ptr for Atom. Patch by Andy Zhang.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150008 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86Subtarget.cpp b/lib/Target/X86/X86Subtarget.cpp
index a9d95d3..f1ef118 100644
--- a/lib/Target/X86/X86Subtarget.cpp
+++ b/lib/Target/X86/X86Subtarget.cpp
@@ -257,6 +257,7 @@
     // Set processor type. Currently only Atom is detected.
     if (Family == 6 && Model == 28) {
       X86ProcFamily = IntelAtom;
+      ToggleFeature(X86::FeatureLeaForSP);
     }
 
     unsigned MaxExtLevel;
@@ -340,6 +341,7 @@
   , IsUAMemFast(false)
   , HasVectorUAMem(false)
   , HasCmpxchg16b(false)
+  , UseLeaForSP(false)
   , PostRAScheduler(false)
   , stackAlignment(4)
   // FIXME: this is a known good value for Yonah. How about others?