Adds a SelectionDAG node X86SegAlloca which will be custom lowered
from DYNAMIC_STACKALLOC.

Two new pseudo instructions (SEG_ALLOCA_32 and SEG_ALLOCA_64) which
will match X86SegAlloca (based on word size) are also added.  They
will be custom emitted to inject the actual stack handling code.

Patch by Sanjoy Das.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@138814 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 2041c3c..a885699 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -10636,6 +10636,7 @@
   case X86ISD::VAARG_64:           return "X86ISD::VAARG_64";
   case X86ISD::WIN_ALLOCA:         return "X86ISD::WIN_ALLOCA";
   case X86ISD::MEMBARRIER:         return "X86ISD::MEMBARRIER";
+  case X86ISD::SEG_ALLOCA:         return "X86ISD::SEG_ALLOCA";
   }
 }