[PATCH] Implement the no_split_stack attribute.

[Aaron Ballman]

On Sat, May 17, 2014 at 2:23 AM, Peter Collingbourne <peter at pcc.me.uk> wrote:
> 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">];

Should this be GCC instead of GNU? (so it can be spelled
[[gnu::no_split_stack]] as well.)

> +  let Subjects = SubjectList<[Function]>;

Should it also apply to templated functions? ObjC methods?

> +  let Documentation = [Undocumented];

Please add documentation for this attribute.

> +}
> +
>  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 {

Missing sema tests for the attribute (that it applies only to
functions, takes no arguments, etc).

~Aaron