[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

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 {

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">;
 

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);

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:

lib/AsmParser/LLToken.h

@@ -200,6 +200,7 @@ enum Kind {
   kw_noalias,
   kw_noundef,
   kw_nobuiltin,
+  kw_nocallback,
   kw_nocapture,
   kw_noduplicate,
   kw_nofree,

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:

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:

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))

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:

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:

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 }