[clang][IR] Add support for leaf attribute

This patch adds support for leaf attribute as an optimization hint
in Clang/LLVM.

Differential Revision: https://reviews.llvm.org/D90275

diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
index 79902c8..61eb86a 100644 (file)
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -1448,6 +1448,13 @@ def LayoutVersion : InheritableAttr, TargetSpecificAttr<TargetMicrosoftCXXABI> {
   let Documentation = [LayoutVersionDocs];
 }
 
+def Leaf : InheritableAttr {
+  let Spellings = [GCC<"leaf">];
+  let Subjects = SubjectList<[Function]>;
+  let Documentation = [LeafDocs];
+  let SimpleHandler = 1;
+}
+
 def LifetimeBound : DeclOrTypeAttr {
   let Spellings = [Clang<"lifetimebound", 0>];
   let Subjects = SubjectList<[ParmVar, ImplicitObjectParameter], ErrorDiag>;

diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 28f35cf..e70596b 100644 (file)
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -3976,6 +3976,22 @@ are used to instantiate the specialization.
   }];
 }
 
+def LeafDocs : Documentation {
+  let Category = DocCatVariable;
+  let Content = [{
+
+The ``leaf`` attribute is used as a compiler hint to improve dataflow analysis
+in library functions. Functions marked with the ``leaf`` attribute are not allowed
+to jump back into the caller's translation unit, whether through invoking a
+callback function, an external function call, use of ``longjmp``, or other means.
+Therefore, they cannot use or modify any data that does not escape the caller function's
+compilation unit.
+
+For more information see
+`gcc documentation <https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html>`
+}];
+}
+
 def NoStackProtectorDocs : Documentation {
   let Category = DocCatFunction;
   let Content = [{

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 5db34b6..73194be 100644 (file)
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -1989,6 +1989,8 @@ void CodeGenModule::ConstructAttributeList(
       FuncAttrs.addAttribute("no_caller_saved_registers");
     if (TargetDecl->hasAttr<AnyX86NoCfCheckAttr>())
       FuncAttrs.addAttribute(llvm::Attribute::NoCfCheck);
+    if (TargetDecl->hasAttr<LeafAttr>())
+      FuncAttrs.addAttribute(llvm::Attribute::NoCallback);
 
     HasOptnone = TargetDecl->hasAttr<OptimizeNoneAttr>();
     if (auto *AllocSize = TargetDecl->getAttr<AllocSizeAttr>()) {

diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 1509485..395d0ef 100644 (file)
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -7715,6 +7715,9 @@ static void ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D,
   case ParsedAttr::AT_AnyX86NoCfCheck:
     handleNoCfCheckAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_Leaf:
+    handleSimpleAttribute<LeafAttr>(S, D, AL);
+    break;
   case ParsedAttr::AT_NoThrow:
     if (!AL.isUsedAsTypeAttr())
       handleSimpleAttribute<NoThrowAttr>(S, D, AL);

diff --git a/clang/test/CodeGen/attr-leaf.c b/clang/test/CodeGen/attr-leaf.c
new file mode 100644 (file)
index 0000000..2b2bacf
--- /dev/null
+++ b/clang/test/CodeGen/attr-leaf.c
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -Oz -o - %s | FileCheck %s
+
+// CHECK: define void @f() local_unnamed_addr [[ATTRS:#[0-9]+]] {
+void f() __attribute__((leaf));
+
+void f()
+{
+}
+
+// CHECK: attributes [[ATTRS]] = { {{.*}}nocallback{{.*}} }

diff --git a/clang/test/Misc/pragma-attribute-supported-attributes-list.test b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
index 0ba6769..cb1e482 100644 (file)
--- a/clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ b/clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -68,6 +68,7 @@
 // CHECK-NEXT: InitPriority (SubjectMatchRule_variable)
 // CHECK-NEXT: InternalLinkage (SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_record)
 // CHECK-NEXT: LTOVisibilityPublic (SubjectMatchRule_record)
+// CHECK-NEXT: Leaf (SubjectMatchRule_function)
 // CHECK-NEXT: LoaderUninitialized (SubjectMatchRule_variable_is_global)
 // CHECK-NEXT: Lockable (SubjectMatchRule_record)
 // CHECK-NEXT: MIGServerRoutine (SubjectMatchRule_function, SubjectMatchRule_objc_method, SubjectMatchRule_block)

diff --git a/clang/test/Sema/attr-leaf.c b/clang/test/Sema/attr-leaf.c
new file mode 100644 (file)
index 0000000..a28ad79
--- /dev/null
+++ b/clang/test/Sema/attr-leaf.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -verify -fsyntax-only %s
+
+void f1() __attribute__((leaf));
+
+void f2() __attribute__((leaf("abc"))); // expected-error {{'leaf' attribute takes no argument}}
+
+int var __attribute__ ((leaf())); // expected-warning {{'leaf' attribute only applies to functions}}
+
+// FIXME: Might diagnose a warning if leaf attribute is used in function definition
+// The leaf attribute has no effect on functions defined within the current compilation unit
+__attribute__((leaf)) void f3() {
+}

diff --git a/llvm/include/llvm/Bitcode/LLVMBitCodes.h b/llvm/include/llvm/Bitcode/LLVMBitCodes.h
index 80fa4ac..a6d2802 100644 (file)
--- a/llvm/include/llvm/Bitcode/LLVMBitCodes.h
+++ b/llvm/include/llvm/Bitcode/LLVMBitCodes.h
@@ -653,6 +653,7 @@ enum AttributeKindCodes {
   ATTR_KIND_NOUNDEF = 68,
   ATTR_KIND_BYREF = 69,
   ATTR_KIND_MUSTPROGRESS = 70,
+  ATTR_KIND_NO_CALLBACK = 71,
 };
 
 enum ComdatSelectionKindCodes {

diff --git a/llvm/include/llvm/IR/Attributes.td b/llvm/include/llvm/IR/Attributes.td
index 762f4d6..30d2975 100644 (file)
--- a/llvm/include/llvm/IR/Attributes.td
+++ b/llvm/include/llvm/IR/Attributes.td
@@ -103,6 +103,9 @@ def NoAlias : EnumAttr<"noalias">;
 /// Callee isn't recognized as a builtin.
 def NoBuiltin : EnumAttr<"nobuiltin">;
 
+/// Function cannot enter into caller's translation unit.
+def NoCallback : EnumAttr<"nocallback">;
+
 /// Function creates no aliases of pointer.
 def NoCapture : EnumAttr<"nocapture">;
 

diff --git a/llvm/lib/AsmParser/LLLexer.cpp b/llvm/lib/AsmParser/LLLexer.cpp
index baabd55..c50e824 100644 (file)
--- a/llvm/lib/AsmParser/LLLexer.cpp
+++ b/llvm/lib/AsmParser/LLLexer.cpp
@@ -653,6 +653,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(nest);
   KEYWORD(noalias);
   KEYWORD(nobuiltin);
+  KEYWORD(nocallback);
   KEYWORD(nocapture);
   KEYWORD(noduplicate);
   KEYWORD(nofree);

diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index 675151e..0c2c107 100644 (file)
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -1353,6 +1353,9 @@ bool LLParser::parseFnAttributeValuePairs(AttrBuilder &B,
       break;
     case lltok::kw_naked: B.addAttribute(Attribute::Naked); break;
     case lltok::kw_nobuiltin: B.addAttribute(Attribute::NoBuiltin); break;
+    case lltok::kw_nocallback:
+      B.addAttribute(Attribute::NoCallback);
+      break;
     case lltok::kw_noduplicate: B.addAttribute(Attribute::NoDuplicate); break;
     case lltok::kw_nofree: B.addAttribute(Attribute::NoFree); break;
     case lltok::kw_noimplicitfloat:

diff --git a/llvm/lib/AsmParser/LLToken.h b/llvm/lib/AsmParser/LLToken.h
index 7dd0fda..32e1165 100644 (file)
--- a/llvm/lib/AsmParser/LLToken.h
+++ b/llvm/lib/AsmParser/LLToken.h
@@ -200,6 +200,7 @@ enum Kind {
   kw_noalias,
   kw_noundef,
   kw_nobuiltin,
+  kw_nocallback,
   kw_nocapture,
   kw_noduplicate,
   kw_nofree,

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 158f8d1..43e4fca 100644 (file)
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1433,6 +1433,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::NoAlias;
   case bitc::ATTR_KIND_NO_BUILTIN:
     return Attribute::NoBuiltin;
+  case bitc::ATTR_KIND_NO_CALLBACK:
+    return Attribute::NoCallback;
   case bitc::ATTR_KIND_NO_CAPTURE:
     return Attribute::NoCapture;
   case bitc::ATTR_KIND_NO_DUPLICATE:

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 5c13738..5b96518 100644 (file)
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -646,6 +646,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_NO_ALIAS;
   case Attribute::NoBuiltin:
     return bitc::ATTR_KIND_NO_BUILTIN;
+  case Attribute::NoCallback:
+    return bitc::ATTR_KIND_NO_CALLBACK;
   case Attribute::NoCapture:
     return bitc::ATTR_KIND_NO_CAPTURE;
   case Attribute::NoDuplicate:

diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index 82350ad..fc0d68e 100644 (file)
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -371,6 +371,8 @@ std::string Attribute::getAsString(bool InAttrGrp) const {
     return "noalias";
   if (hasAttribute(Attribute::NoBuiltin))
     return "nobuiltin";
+  if (hasAttribute(Attribute::NoCallback))
+    return "nocallback";
   if (hasAttribute(Attribute::NoCapture))
     return "nocapture";
   if (hasAttribute(Attribute::NoDuplicate))

diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index ac44a95..71bb94e 100644 (file)
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -1597,6 +1597,7 @@ static bool isFuncOnlyAttr(Attribute::AttrKind Kind) {
   case Attribute::NoReturn:
   case Attribute::NoSync:
   case Attribute::WillReturn:
+  case Attribute::NoCallback:
   case Attribute::NoCfCheck:
   case Attribute::NoUnwind:
   case Attribute::NoInline:

diff --git a/llvm/lib/Transforms/Utils/CodeExtractor.cpp b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
index 1d01e40..91297b8 100644 (file)
--- a/llvm/lib/Transforms/Utils/CodeExtractor.cpp
+++ b/llvm/lib/Transforms/Utils/CodeExtractor.cpp
@@ -946,6 +946,7 @@ Function *CodeExtractor::constructFunction(const ValueSet &inputs,
       case Attribute::NoRecurse:
       case Attribute::InlineHint:
       case Attribute::MinSize:
+      case Attribute::NoCallback:
       case Attribute::NoDuplicate:
       case Attribute::NoFree:
       case Attribute::NoImplicitFloat:

diff --git a/llvm/test/Bitcode/attributes.ll b/llvm/test/Bitcode/attributes.ll
index baafc70..36c9ff7 100644 (file)
--- a/llvm/test/Bitcode/attributes.ll
+++ b/llvm/test/Bitcode/attributes.ll
@@ -404,6 +404,12 @@ define void @f68() mustprogress
   ret void
 }
 
+; CHECK; define void @f69() #43
+define void @f70() nocallback
+{
+  ret void
+}
+
 ; CHECK: attributes #0 = { noreturn }
 ; CHECK: attributes #1 = { nounwind }
 ; CHECK: attributes #2 = { readnone }
@@ -446,4 +452,5 @@ define void @f68() mustprogress
 ; CHECK: attributes #39 = { sanitize_memtag }
 ; CHECK: attributes #40 = { null_pointer_is_valid }
 ; CHECK: attributes #41 = { mustprogress }
+; CHECK: attributes #42 = { nocallback }
 ; CHECK: attributes #[[NOBUILTIN]] = { nobuiltin }