Fix broken getAttributeSpellingListIndex for pragma attributes

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.

Patch by: mikerice

Differential Revision: https://reviews.llvm.org/D36473

llvm-svn: 310483
diff --git a/clang/lib/Sema/SemaStmtAttr.cpp b/clang/lib/Sema/SemaStmtAttr.cpp
index 4ee3412..ad82a44 100644
--- a/clang/lib/Sema/SemaStmtAttr.cpp
+++ b/clang/lib/Sema/SemaStmtAttr.cpp
@@ -100,16 +100,15 @@
     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;
@@ -121,7 +120,6 @@
     }
   } else {
     // #pragma clang loop ...
-    Spelling = LoopHintAttr::Pragma_clang_loop;
     assert(OptionLoc && OptionLoc->Ident &&
            "Attribute must have valid option info.");
     Option = llvm::StringSwitch<LoopHintAttr::OptionType>(