[PATCH] Implement the no_split_stack attribute.

[Peter Collingbourne]

This is a GNU attribute that allows split stacks to be turned off on a
per-function basis.

http://reviews.llvm.org/D3817

Files:
  include/clang/Basic/Attr.td
  lib/CodeGen/CGCall.cpp
  lib/Sema/SemaDeclAttr.cpp
  test/CodeGen/split-stacks.c

Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -823,6 +823,12 @@
   let Documentation = [Undocumented];
 }
 
+def NoSplitStack : InheritableAttr {
+  let Spellings = [GNU<"no_split_stack">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [Undocumented];
+}
+
 def NonNull : InheritableAttr {
   let Spellings = [GCC<"nonnull">];
   let Subjects = SubjectList<[ObjCMethod, HasFunctionProto, ParmVar], WarnDiag,
Index: lib/CodeGen/CGCall.cpp
===================================================================
--- lib/CodeGen/CGCall.cpp
+++ lib/CodeGen/CGCall.cpp
@@ -1117,7 +1117,8 @@
     FuncAttrs.addAttribute(llvm::Attribute::NoRedZone);
   if (CodeGenOpts.NoImplicitFloat)
     FuncAttrs.addAttribute(llvm::Attribute::NoImplicitFloat);
-  if (CodeGenOpts.EnableSegmentedStacks)
+  if (CodeGenOpts.EnableSegmentedStacks &&
+      !(TargetDecl && TargetDecl->hasAttr<NoSplitStackAttr>()))
     FuncAttrs.addAttribute("split-stack");
 
   if (AttrOnCallSite) {
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -4173,6 +4173,9 @@
   case AttributeList::AT_NoCommon:
     handleSimpleAttribute<NoCommonAttr>(S, D, Attr);
     break;
+  case AttributeList::AT_NoSplitStack:
+    handleSimpleAttribute<NoSplitStackAttr>(S, D, Attr);
+    break;
   case AttributeList::AT_NonNull:
     if (ParmVarDecl *PVD = dyn_cast<ParmVarDecl>(D))
       handleNonNullAttrParameter(S, PVD, Attr);
Index: test/CodeGen/split-stacks.c
===================================================================
--- test/CodeGen/split-stacks.c
+++ test/CodeGen/split-stacks.c
@@ -5,13 +5,21 @@
   return 0;
 }
 
+__attribute__((no_split_stack))
+int nosplit() {
+  return 0;
+}
+
 int main() {
   return foo();
 }
 
-// CHECK-SEGSTK: define i32 @foo() #0 {
-// CHECK-SEGSTK: define i32 @main() #0 {
-// CHECK-SEGSTK: #0 = { {{.*}} "split-stack" {{.*}} }
+// CHECK-SEGSTK: define i32 @foo() [[SS:#[0-9]+]] {
+// CHECK-SEGSTK: define i32 @nosplit() [[NSS:#[0-9]+]] {
+// CHECK-SEGSTK: define i32 @main() [[SS]] {
+// CHECK-SEGSTK-NOT: [[NSS]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-SEGSTK: [[SS]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-SEGSTK-NOT: [[NSS]] = { {{.*}} "split-stack" {{.*}} }
 
 // CHECK-NOSEGSTK: define i32 @foo() #0 {
 // CHECK-NOSEGSTK: define i32 @main() #0 {
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