[PATCH] Add a "no-split-stack" function attribute.

[Luqman Aden]

This disable emission of segmented-stack prologues on a per-function basis, even if segmented stacks are turned on globally.

http://llvm-reviews.chandlerc.com/D1905

Files:
  lib/CodeGen/PrologEpilogInserter.cpp
  test/CodeGen/X86/segmented-stacks.ll

Index: lib/CodeGen/PrologEpilogInserter.cpp
===================================================================
--- lib/CodeGen/PrologEpilogInserter.cpp
+++ lib/CodeGen/PrologEpilogInserter.cpp
@@ -707,7 +707,8 @@
   // we've been asked for it.  This, when linked with a runtime with support
   // for segmented stacks (libgcc is one), will result in allocating stack
   // space in small chunks instead of one large contiguous block.
-  if (Fn.getTarget().Options.EnableSegmentedStacks)
+  if (Fn.getTarget().Options.EnableSegmentedStacks &&
+      !Fn.getFunction()->hasFnAttribute("no-split-stack"))
     TFI.adjustForSegmentedStacks(Fn);
 
   // Emit additional code that is required to explicitly handle the stack in
Index: test/CodeGen/X86/segmented-stacks.ll
===================================================================
--- test/CodeGen/X86/segmented-stacks.ll
+++ test/CodeGen/X86/segmented-stacks.ll
@@ -383,3 +383,29 @@
 ; X32-Darwin-NEXT: ret
 
 }
+
+define void @test_no_split_stack() #0 {
+        %mem = alloca i32, i32 10
+        call void @dummy_use (i32* %mem, i32 10)
+        ret void
+
+; Don't emit __morestack if no-split-stack
+
+; X32-Linux-LABEL:  test_no_split_stack:
+; X32-Linux-NOT:  __morestack
+
+; X64-Linux-LABEL:  test_no_split_stack:
+; X64-Linux-NOT:  __morestack
+
+; X32-Darwin-LABEL:  test_no_split_stack:
+; X32-Darwin-NOT:  __morestack
+
+; X64-Darwin-LABEL:  test_no_split_stack:
+; X64-Darwin-NOT:  __morestack
+
+; X64-FreeBSD-LABEL:  test_no_split_stack:
+; X64-FreeBSD-NOT:  __morestack
+
+}
+
+attributes #0 = { "no-split-stack" }
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