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

lib/Target/X86/X86InstrCompiler.td

@@ -106,6 +106,26 @@ let Defs = [EAX, ESP, EFLAGS], Uses = [ESP] in
   def WIN_ALLOCA : I<0, Pseudo, (outs), (ins),
                      "# dynamic stack allocation",
                      [(X86WinAlloca)]>;
+
+// When using segmented stacks these are lowered into instructions which first
+// check if the current stacklet has enough free memory. If it does, memory is
+// allocated by bumping the stack pointer. Otherwise memory is allocated from 
+// the heap.
+
+let Defs = [EAX, ESP, EFLAGS], Uses = [ESP, EAX] in
+def SEG_ALLOCA_32 : I<0, Pseudo, (outs GR32:$dst), (ins GR32:$size),
+                      "# variable sized alloca for segmented stacks",
+                      [(set GR32:$dst,
+                         (X86SegAlloca GR32:$size))]>,
+                    Requires<[In32BitMode]>;
+
+let Defs = [RAX, RSP, EFLAGS], Uses = [RSP, RAX] in
+def SEG_ALLOCA_64 : I<0, Pseudo, (outs GR64:$dst), (ins GR64:$size),
+                      "# variable sized alloca for segmented stacks",
+                      [(set GR64:$dst,
+                         (X86SegAlloca GR64:$size))]>,
+                    Requires<[In64BitMode]>;
+
 }