[clang] Add no_builtin attribute

Summary:
This is a follow up on https://reviews.llvm.org/D61634
This patch is simpler and only adds the no_builtin attribute.

Reviewers: tejohnson, courbet, theraven, t.p.northover, jdoerfert

Subscribers: mgrang, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D68028

3 files changed, 96 insertions, 4 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index b74f6f94242..62e8fa03701 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1853,11 +1853,27 @@ void CodeGenModule::ConstructAttributeList(
     if (const FunctionDecl *Fn = dyn_cast<FunctionDecl>(TargetDecl)) {
       AddAttributesFromFunctionProtoType(
           getContext(), FuncAttrs, Fn->getType()->getAs<FunctionProtoType>());
-      // Don't use [[noreturn]] or _Noreturn for a call to a virtual function.
-      // These attributes are not inherited by overloads.
       const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Fn);
-      if (Fn->isNoReturn() && !(AttrOnCallSite && MD && MD->isVirtual()))
-        FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
+      const bool IsVirtualCall = MD && MD->isVirtual();
+      // Don't use [[noreturn]], _Noreturn or [[no_builtin]] for a call to a
+      // virtual function. These attributes are not inherited by overloads.
+      if (!(AttrOnCallSite && IsVirtualCall)) {
+        if (Fn->isNoReturn())
+          FuncAttrs.addAttribute(llvm::Attribute::NoReturn);
+
+        if (const auto *NBA = TargetDecl->getAttr<NoBuiltinAttr>()) {
+          bool HasWildcard = llvm::is_contained(NBA->builtinNames(), "*");
+          if (HasWildcard)
+            FuncAttrs.addAttribute("no-builtins");
+          else
+            for (StringRef BuiltinName : NBA->builtinNames()) {
+              SmallString<32> AttributeName;
+              AttributeName += "no-builtin-";
+              AttributeName += BuiltinName;
+              FuncAttrs.addAttribute(AttributeName);
+            }
+        }
+      }
     }
 
     // 'const', 'pure' and 'noalias' attributed functions are also nounwind.
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 6202391ee0b..aba7049b0a5 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9529,6 +9529,29 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     }
   }
 
+  // Diagnose no_builtin attribute on function declaration that are not a
+  // definition.
+  // FIXME: We should really be doing this in
+  // SemaDeclAttr.cpp::handleNoBuiltinAttr, unfortunately we only have access to
+  // the FunctionDecl and at this point of the code
+  // FunctionDecl::isThisDeclarationADefinition() which always returns `false`
+  // because Sema::ActOnStartOfFunctionDef has not been called yet.
+  if (const auto *NBA = NewFD->getAttr<NoBuiltinAttr>())
+    switch (D.getFunctionDefinitionKind()) {
+    case FDK_Defaulted:
+    case FDK_Deleted:
+      Diag(NBA->getLocation(),
+           diag::err_attribute_no_builtin_on_defaulted_deleted_function)
+          << NBA->getSpelling();
+      break;
+    case FDK_Declaration:
+      Diag(NBA->getLocation(), diag::err_attribute_no_builtin_on_non_definition)
+          << NBA->getSpelling();
+      break;
+    case FDK_Definition:
+      break;
+    }
+
   return NewFD;
 }
 
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index abbd597a26d..99eb23c3fe6 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1069,6 +1069,56 @@ static void handleDiagnoseIfAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
       S.Context, AL, Cond, Msg, DiagType, ArgDependent, cast<NamedDecl>(D)));
 }
 
+static void handleNoBuiltinAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  static constexpr const StringRef kWildcard = "*";
+
+  llvm::SmallVector<StringRef, 16> Names;
+  bool HasWildcard = false;
+
+  const auto AddBuiltinName = [&Names, &HasWildcard](StringRef Name) {
+    if (Name == kWildcard)
+      HasWildcard = true;
+    Names.push_back(Name);
+  };
+
+  // Add previously defined attributes.
+  if (const auto *NBA = D->getAttr<NoBuiltinAttr>())
+    for (StringRef BuiltinName : NBA->builtinNames())
+      AddBuiltinName(BuiltinName);
+
+  // Add current attributes.
+  if (AL.getNumArgs() == 0)
+    AddBuiltinName(kWildcard);
+  else
+    for (unsigned I = 0, E = AL.getNumArgs(); I != E; ++I) {
+      StringRef BuiltinName;
+      SourceLocation LiteralLoc;
+      if (!S.checkStringLiteralArgumentAttr(AL, I, BuiltinName, &LiteralLoc))
+        return;
+
+      if (Builtin::Context::isBuiltinFunc(BuiltinName.data()))
+        AddBuiltinName(BuiltinName);
+      else
+        S.Diag(LiteralLoc, diag::warn_attribute_no_builtin_invalid_builtin_name)
+            << BuiltinName << AL.getAttrName()->getName();
+    }
+
+  // Repeating the same attribute is fine.
+  llvm::sort(Names);
+  Names.erase(std::unique(Names.begin(), Names.end()), Names.end());
+
+  // Empty no_builtin must be on its own.
+  if (HasWildcard && Names.size() > 1)
+    S.Diag(D->getLocation(),
+           diag::err_attribute_no_builtin_wildcard_or_builtin_name)
+        << AL.getAttrName()->getName();
+
+  if (D->hasAttr<NoBuiltinAttr>())
+    D->dropAttr<NoBuiltinAttr>();
+  D->addAttr(::new (S.Context)
+                 NoBuiltinAttr(S.Context, AL, Names.data(), Names.size()));
+}
+
 static void handlePassObjectSizeAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   if (D->hasAttr<PassObjectSizeAttr>()) {
     S.Diag(D->getBeginLoc(), diag::err_attribute_only_once_per_parameter) << AL;
@@ -6608,6 +6658,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_DiagnoseIf:
     handleDiagnoseIfAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_NoBuiltin:
+    handleNoBuiltinAttr(S, D, AL);
+    break;
   case ParsedAttr::AT_ExtVectorType:
     handleExtVectorTypeAttr(S, D, AL);
     break;