Fix broken getAttributeSpellingListIndex for pragma attributes

[mikerice]

Summary

We noticed when implementing a new pragma that the TableGen-generated function getAttributeSpellingListIndex() did not work for pragma attributes. It relies on the values in the enum AttributeList::Syntax and a new value AS_ContextSensitiveKeyword was added changing the value for AS_Pragma. Apparently no tests failed since no pragmas currently make use of the generated function.

To fix this we can move AS_Pragma back to the value that TableGen code expects. Also to prevent changes in the enum from breaking that routine again I added calls to getAttributeSpellingListIndex() in the unroll pragma code. That will cause some lit test failures if the order is changed. I added a comment to remind of this issue in the future.

This assumes we don’t need/want full TableGen support for AS_ContextSensitiveKeyword. It currently only appears in getAttrKind and no other TableGen-generated routines.

[aaron.ballman]

LGTM, good catch!

include/clang/Sema/AttributeList.h

enum Syntax {
     /// [[...]]
     AS_CXX11,
     /// __declspec(...)
     AS_Declspec,
     /// [uuid("...")] class Foo
     AS_Microsoft,
     /// __ptr16, alignas(...), etc.
     AS_Keyword,
-    /// Context-sensitive version of a keyword attribute.
-    AS_ContextSensitiveKeyword,
     /// #pragma ...
     AS_Pragma,
+    // Note TableGen depends on the order above.  Do not add or change the order
+    // without adding related code to TableGen/ClangAttrEmitter.cpp.
+    /// Context-sensitive version of a keyword attribute.
+    AS_ContextSensitiveKeyword,
   };
 
 private:
   IdentifierInfo *AttrName;
   IdentifierInfo *ScopeName;
   SourceRange AttrRange;
   SourceLocation ScopeLoc;
   SourceLocation EllipsisLoc;

lib/Sema/SemaStmtAttr.cpp

const char *Pragma =
         llvm::StringSwitch<const char *>(PragmaNameLoc->Ident->getName())
             .Case("unroll", "#pragma unroll")
             .Case("nounroll", "#pragma nounroll")
             .Default("#pragma clang loop");
     S.Diag(St->getLocStart(), diag::err_pragma_loop_precedes_nonloop) << Pragma;
     return nullptr;
   }
 
-  LoopHintAttr::Spelling Spelling;
+  LoopHintAttr::Spelling Spelling =
+      LoopHintAttr::Spelling(A.getAttributeSpellingListIndex());
   LoopHintAttr::OptionType Option;
   LoopHintAttr::LoopHintState State;
   if (PragmaNoUnroll) {
     // #pragma nounroll
-    Spelling = LoopHintAttr::Pragma_nounroll;
     Option = LoopHintAttr::Unroll;
     State = LoopHintAttr::Disable;
   } else if (PragmaUnroll) {
-    Spelling = LoopHintAttr::Pragma_unroll;
     if (ValueExpr) {
       // #pragma unroll N
       Option = LoopHintAttr::UnrollCount;
       State = LoopHintAttr::Numeric;
     } else {
       // #pragma unroll
       Option = LoopHintAttr::Unroll;
       State = LoopHintAttr::Enable;
     }
   } else {
     // #pragma clang loop ...
-    Spelling = LoopHintAttr::Pragma_clang_loop;
     assert(OptionLoc && OptionLoc->Ident &&
            "Attribute must have valid option info.");
     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(
                  OptionLoc->Ident->getName())
                  .Case("vectorize", LoopHintAttr::Vectorize)
                  .Case("vectorize_width", LoopHintAttr::VectorizeWidth)
                  .Case("interleave", LoopHintAttr::Interleave)
                  .Case("interleave_count", LoopHintAttr::InterleaveCount)