Implement the no_split_stack attribute.

[pcc]

Summary

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

[pcc]

Add tests and docs

[pcc]

Closed by commit rL209167 (authored by @pcc).

include/clang/Basic/Attr.td

 }
 
 def NoMips16 : InheritableAttr, TargetSpecificAttr<TargetMips> {
   let Spellings = [GCC<"nomips16">];
   let Subjects = SubjectList<[Function], ErrorDiag>;
   let Documentation = [Undocumented];
 }
 
+def NoSplitStack : InheritableAttr {
+  let Spellings = [GCC<"no_split_stack">];
+  let Subjects = SubjectList<[Function], ErrorDiag>;
+  let Documentation = [NoSplitStackDocs];
+}
+
 def NonNull : InheritableAttr {
   let Spellings = [GCC<"nonnull">];
   let Subjects = SubjectList<[ObjCMethod, HasFunctionProto, ParmVar], WarnDiag,
                              "ExpectedFunctionMethodOrParameter">;
   let Args = [VariadicUnsignedArgument<"Args">];
   let AdditionalMembers =
 [{bool isNonNull(unsigned idx) const {
     for (const auto &V : args())

include/clang/Basic/AttrDocs.td

if (a > n) {
     bar();
   }
 
 where the call to "nodupfunc" is duplicated and sunk into the two branches
 of the condition.
   }];
 }
 
+def NoSplitStackDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``no_split_stack`` attribute disables the emission of the split stack
+preamble for a particular function. It has no effect if ``-fsplit-stack``
+is not specified.
+  }];
+}
+
 def ObjCRequiresSuperDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{
 Some Objective-C classes allow a subclass to override a particular method in a
 parent class but expect that the overriding method also calls the overridden
 method in the parent class. For these cases, we provide an attribute to
 designate that a method requires a "call to ``super``" in the overriding
 method in the subclass.

lib/CodeGen/CGCall.cpp

void CodeGenModule::ConstructAttributeList(const CGFunctionInfo &FI,
   if (CodeGenOpts.OptimizeSize)
     FuncAttrs.addAttribute(llvm::Attribute::OptimizeForSize);
   if (CodeGenOpts.OptimizeSize == 2)
     FuncAttrs.addAttribute(llvm::Attribute::MinSize);
   if (CodeGenOpts.DisableRedZone)
     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) {
     // Attributes that should go on the call site only.
     if (!CodeGenOpts.SimplifyLibCalls)
       FuncAttrs.addAttribute(llvm::Attribute::NoBuiltin);
   } else {
     // Attributes that should go on the function, but not the call site.

lib/Sema/SemaDeclAttr.cpp

case AttributeList::AT_MayAlias:
     handleSimpleAttribute<MayAliasAttr>(S, D, Attr);
     break;
   case AttributeList::AT_Mode:
     handleModeAttr(S, D, Attr);
     break;
   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);
     else
       handleNonNullAttr(S, D, Attr);
     break;
   case AttributeList::AT_ReturnsNonNull:
     handleReturnsNonNullAttr(S, D, Attr);

test/CodeGen/split-stacks.c

 // RUN: %clang -target x86_64-linux-gnu -fsplit-stack -S %s -emit-llvm -o - | FileCheck -check-prefix=CHECK-SEGSTK %s
 // RUN: %clang -target x86_64-linux-gnu -S %s -emit-llvm -o - | FileCheck -check-prefix=CHECK-NOSEGSTK %s
 
 int foo() {
   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 {
 // CHECK-NOSEGSTK-NOT: #0 = { {{.*}} "split-stack" {{.*}} }

test/CodeGenCXX/split-stacks.cpp

+// RUN: %clang -target x86_64-linux-gnu -fsplit-stack -S -std=c++11 %s -emit-llvm -o - | FileCheck -check-prefix=CHECK-SEGSTK %s
+// RUN: %clang -target x86_64-linux-gnu -S -std=c++11 %s -emit-llvm -o - | FileCheck -check-prefix=CHECK-NOSEGSTK %s
+
+int foo() {
+  return 0;
+}
+
+template <typename T>
+[[gnu::no_split_stack]]
+int tnosplit() {
+  return 0;
+}
+
+[[gnu::no_split_stack]]
+int nosplit() {
+  return tnosplit<int>();
+}
+
+// CHECK-SEGSTK: define i32 @_Z3foov() [[SS:#[0-9]+]] {
+// CHECK-SEGSTK: define i32 @_Z7nosplitv() [[NSS1:#[0-9]+]] {
+// CHECK-SEGSTK: define linkonce_odr i32 @_Z8tnosplitIiEiv() [[NSS2:#[0-9]+]] {
+// CHECK-SEGSTK-NOT: [[NSS1]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-SEGSTK-NOT: [[NSS2]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-SEGSTK: [[SS]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-SEGSTK-NOT: [[NSS1]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-SEGSTK-NOT: [[NSS2]] = { {{.*}} "split-stack" {{.*}} }
+
+// CHECK-NOSEGSTK: define i32 @_Z3foov() [[NSS0:#[0-9]+]] {
+// CHECK-NOSEGSTK: define i32 @_Z7nosplitv() [[NSS1:#[0-9]+]] {
+// CHECK-NOSEGSTK: define linkonce_odr i32 @_Z8tnosplitIiEiv() [[NSS2:#[0-9]+]] {
+// CHECK-NOSEGSTK-NOT: [[NSS1]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-NOSEGSTK-NOT: [[NSS2]] = { {{.*}} "split-stack" {{.*}} }
+// CHECK-NOSEGSTK-NOT: [[NSS3]] = { {{.*}} "split-stack" {{.*}} }

test/SemaCXX/attr-no-split-stack.cpp

+// RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s
+
+int i __attribute__((no_split_stack)); // expected-error {{'no_split_stack' attribute only applies to functions}}
+
+void f1() __attribute__((no_split_stack));
+void f2() __attribute__((no_split_stack(1))); // expected-error {{'no_split_stack' attribute takes no arguments}}
+
+template <typename T>
+void tf1() __attribute__((no_split_stack));
+
+int f3(int __attribute__((no_split_stack)), int); // expected-error{{'no_split_stack' attribute only applies to functions}}
+
+struct A {
+  int f __attribute__((no_split_stack));  // expected-error{{'no_split_stack' attribute only applies to functions}}
+  void mf1() __attribute__((no_split_stack));
+  static void mf2() __attribute__((no_split_stack));
+};
+
+int ci [[gnu::no_split_stack]]; // expected-error {{'no_split_stack' attribute only applies to functions}}
+
+[[gnu::no_split_stack]] void cf1();
+[[gnu::no_split_stack(1)]] void cf2(); // expected-error {{'no_split_stack' attribute takes no arguments}}
+
+template <typename T>
+[[gnu::no_split_stack]]
+void ctf1();
+
+int cf3(int c[[gnu::no_split_stack]], int); // expected-error{{'no_split_stack' attribute only applies to functions}}
+
+struct CA {
+  int f [[gnu::no_split_stack]];  // expected-error{{'no_split_stack' attribute only applies to functions}}
+  [[gnu::no_split_stack]] void mf1();
+  [[gnu::no_split_stack]] static void mf2();
+};