Add LLVMGetAttrKindID in the C API in order to facilitate migration away from LLVMAttribute

Summary:
LLVMAttribute has outlived its utility and is becoming a problem for C API users that what to use all the LLVM attributes. In order to help moving away from LLVMAttribute in a smooth manner, this diff introduce LLVMGetAttrKindIDInContext, which can be used instead of the enum values.

See D18749 for reference.

Reviewers: Wallbraker, whitequark, joker.eph, echristo, rafael

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D19081

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266842 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ReleaseNotes.rst

@@ -54,6 +54,9 @@ Non-comprehensive list of changes in this release
 * The C API function LLVMGetDataLayout is deprecated
   in favor of LLVMGetDataLayoutStr.
 
+* The C API enum LLVMAttribute is deprecated in favor of
+  LLVMGetAttrKindID.
+
 * ``TargetFrameLowering::eliminateCallFramePseudoInstr`` now returns an
   iterator to the next instruction instead of ``void``. Targets that previously
   did ``MBB.erase(I); return;`` now probably want ``return MBB.erase(I);``.

include/llvm-c/Core.h

@@ -476,6 +476,19 @@ unsigned LLVMGetMDKindIDInContext(LLVMContextRef C, const char *Name,
                                   unsigned SLen);
 unsigned LLVMGetMDKindID(const char *Name, unsigned SLen);
 
+/**
+ * Return an unique id given the name of a target independent attribute,
+ * or 0 if no attribute by that name exists.
+ *
+ * See http://llvm.org/docs/LangRef.html#parameter-attributes
+ * and http://llvm.org/docs/LangRef.html#function-attributes
+ * for the list of available attributes.
+ *
+ * NB: Attribute names and/or id are subject to change without
+ * going through the C API deprecation cycle.
+ */
+unsigned LLVMGetAttrKindID(const char *Name, size_t SLen);
+
 /**
  * @}
  */

lib/IR/Core.cpp

@@ -13,6 +13,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm-c/Core.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "AttributeImpl.h"
 #include "llvm/Bitcode/ReaderWriter.h"
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/CallSite.h"
@@ -119,6 +121,18 @@ unsigned LLVMGetMDKindID(const char *Name, unsigned SLen) {
   return LLVMGetMDKindIDInContext(LLVMGetGlobalContext(), Name, SLen);
 }
 
+#define GET_ATTR_KIND_FROM_NAME
+#include "AttributesCompatFunc.inc"
+
+unsigned LLVMGetAttrKindID(const char *Name, size_t SLen) {
+  auto K = getAttrKindFromName(StringRef(Name, SLen));
+  if (K == Attribute::None) {
+    return 0;
+  }
+
+  return AttributeImpl::getAttrMask(K);
+}
+
 char *LLVMGetDiagInfoDescription(LLVMDiagnosticInfoRef DI) {
   std::string MsgStorage;
   raw_string_ostream Stream(MsgStorage);

utils/TableGen/Attributes.cpp

@@ -27,6 +27,7 @@ public:
 
 private:
   void emitTargetIndependentEnums(raw_ostream &OS);
+  void emitConversionFn(raw_ostream &OS);
   void emitFnAttrCompatCheck(raw_ostream &OS, bool IsStringAttr);
 
   void printEnumAttrClasses(raw_ostream &OS,
@@ -52,6 +53,27 @@ void Attributes::emitTargetIndependentEnums(raw_ostream &OS) {
   OS << "#endif\n";
 }
 
+void Attributes::emitConversionFn(raw_ostream &OS) {
+  OS << "#ifdef GET_ATTR_KIND_FROM_NAME\n";
+  OS << "#undef GET_ATTR_KIND_FROM_NAME\n";
+
+  std::vector<Record*> Attrs =
+      Records.getAllDerivedDefinitions("EnumAttr");
+
+  OS << "static Attribute::AttrKind getAttrKindFromName(StringRef AttrName) {\n";
+  OS << "  return StringSwitch<Attribute::AttrKind>(AttrName)\n";
+
+  for (auto A : Attrs) {
+    OS << "    .Case(\"" << A->getValueAsString("AttrString");
+    OS << "\", Attribute::" << A->getName() << ")\n";
+  }
+
+  OS << "    .Default(Attribute::None);\n";
+  OS << "}\n\n";
+
+  OS << "#endif\n";
+}
+
 void Attributes::emitFnAttrCompatCheck(raw_ostream &OS, bool IsStringAttr) {
   OS << "#ifdef GET_ATTR_COMPAT_FUNC\n";
   OS << "#undef GET_ATTR_COMPAT_FUNC\n";
@@ -144,6 +166,7 @@ void Attributes::printStrBoolAttrClasses(raw_ostream &OS,
 
 void Attributes::emit(raw_ostream &OS) {
   emitTargetIndependentEnums(OS);
+  emitConversionFn(OS);
   emitFnAttrCompatCheck(OS, false);
 }