Add support for referencable labels for attribute documentation

The existing mechanism being used is to manually add a reference in the
documentation. These references link to the beginning of the text rather
than the heading for the attribute which is what this PR allows.

Author: ojhunt

clang/include/clang/Basic/Attr.td

@@ -55,6 +55,9 @@ class Documentation {
   // When set, specifies that the attribute is deprecated and can optionally
   // specify a replacement attribute.
   DocDeprecated Deprecated;
+
+  // When set, specifies a label that can be used to reference the documentation
+  string Label = "";
 }
 
 // Specifies that the attribute is explicitly omitted from the documentation,

clang/include/clang/Basic/AttrDocs.td

@@ -3360,9 +3360,8 @@ def NoSanitizeAddressDocs : Documentation {
   // This function has multiple distinct spellings, and so it requires a custom
   // heading to be specified. The most common spelling is sufficient.
   let Heading = "no_sanitize_address, no_address_safety_analysis";
+  let Label = "langext-address_sanitizer";
   let Content = [{
-.. _langext-address_sanitizer:
-
 Use ``__attribute__((no_sanitize_address))`` on a function or a global
 variable declaration to specify that address safety instrumentation
 (e.g. AddressSanitizer) should not be applied.
@@ -3372,9 +3371,8 @@ variable declaration to specify that address safety instrumentation
 def NoSanitizeThreadDocs : Documentation {
   let Category = DocCatFunction;
   let Heading = "no_sanitize_thread";
+  let Label = "langext-thread_sanitizer";
   let Content = [{
-.. _langext-thread_sanitizer:
-
 Use ``__attribute__((no_sanitize_thread))`` on a function declaration to
 specify that checks for data races on plain (non-atomic) memory accesses should
 not be inserted by ThreadSanitizer. The function is still instrumented by the
@@ -3385,9 +3383,8 @@ tool to avoid false positives and provide meaningful stack traces.
 def NoSanitizeMemoryDocs : Documentation {
   let Category = DocCatFunction;
   let Heading = "no_sanitize_memory";
+  let Label = "langext-memory_sanitizer";
   let Content = [{
-.. _langext-memory_sanitizer:
-
 Use ``__attribute__((no_sanitize_memory))`` on a function declaration to
 specify that checks for uninitialized memory should not be inserted
 (e.g. by MemorySanitizer). The function may still be instrumented by the tool
@@ -3398,9 +3395,8 @@ to avoid false positives in other places.
 def CFICanonicalJumpTableDocs : Documentation {
   let Category = DocCatFunction;
   let Heading = "cfi_canonical_jump_table";
+  let Label = "langext-cfi_canonical_jump_table";
   let Content = [{
-.. _langext-cfi_canonical_jump_table:
-
 Use ``__attribute__((cfi_canonical_jump_table))`` on a function declaration to
 make the function's CFI jump table canonical. See :ref:`the CFI documentation
 <cfi-canonical-jump-tables>` for more details.

clang/utils/TableGen/ClangAttrEmitter.cpp

@@ -5178,6 +5178,9 @@ GetAttributeHeadingAndSpellings(const Record &Documentation,
 
 static void WriteDocumentation(const RecordKeeper &Records,
                                const DocumentationData &Doc, raw_ostream &OS) {
+  if (const StringRef label = Doc.Documentation->getValueAsString("Label");
+      !label.empty())
+    OS << ".. _" << label << ":\n\n";
   OS << Doc.Heading << "\n" << std::string(Doc.Heading.length(), '-') << "\n";
 
   // List what spelling syntaxes the attribute supports.