Add Attribute NoThrow as an Exception Specifier Type

In response to https://bugs.llvm.org/show_bug.cgi?id=33235, it became
clear that the current mechanism of hacking through checks for the
exception specification of a function gets confused really quickly when
there are alternate exception specifiers.

This patch introcues EST_NoThrow, which is the equivilent of
EST_noexcept when caused by EST_noThrow. The existing implementation is
left in place to cover functions with no FunctionProtoType.

Differential Revision: https://reviews.llvm.org/D62435

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@362119 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 57 insertions, 1 deletions

diff --git a/lib/Sema/SemaType.cpp b/lib/Sema/SemaType.cpp
index 91743bb59f..e0d43a780e 100644
--- a/lib/Sema/SemaType.cpp
+++ b/lib/Sema/SemaType.cpp
@@ -130,6 +130,7 @@ static void diagnoseBadTypeAttribute(Sema &S, const ParsedAttr &attr,
   case ParsedAttr::AT_Regparm:                                                 \
   case ParsedAttr::AT_AnyX86NoCallerSavedRegisters:                            \
   case ParsedAttr::AT_AnyX86NoCfCheck:                                         \
+  case ParsedAttr::AT_NoThrow:                                                 \
     CALLING_CONV_ATTRS_CASELIST
 
 // Microsoft-specific type qualifiers.
@@ -4516,7 +4517,7 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
       // If the function declarator has a prototype (i.e. it is not () and
       // does not have a K&R-style identifier list), then the arguments are part
       // of the type, otherwise the argument list is ().
-      const DeclaratorChunk::FunctionTypeInfo &FTI = DeclType.Fun;
+      DeclaratorChunk::FunctionTypeInfo &FTI = DeclType.Fun;
       IsQualifiedFunction =
           FTI.hasMethodTypeQualifiers() || FTI.hasRefQualifier();
 
@@ -6945,6 +6946,61 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state, ParsedAttr &attr,
     return true;
   }
 
+  if (attr.getKind() == ParsedAttr::AT_NoThrow) {
+    if (S.CheckAttrNoArgs(attr))
+      return true;
+
+    // Delay if this is not a function type.
+    if (!unwrapped.isFunctionType())
+      return false;
+
+    // Otherwise we can process right away.
+    auto *Proto = unwrapped.get()->getAs<FunctionProtoType>();
+
+    // In the case where this is a FunctionNoProtoType instead of a
+    // FunctionProtoType, let the existing NoThrowAttr implementation do its
+    // thing.
+    if (!Proto)
+      return false;
+
+    attr.setUsedAsTypeAttr();
+
+    // MSVC ignores nothrow if it is in conflict with an explicit exception
+    // specification.
+    if (Proto->hasExceptionSpec()) {
+      switch (Proto->getExceptionSpecType()) {
+      case EST_None:
+        llvm_unreachable("This doesn't have an exception spec!");
+        LLVM_FALLTHROUGH;
+      case EST_DynamicNone:
+      case EST_BasicNoexcept:
+      case EST_NoexceptTrue:
+      case EST_NoThrow:
+        // Exception spec doesn't conflict with nothrow, so don't warn.
+        break;
+
+      case EST_Dynamic:
+      case EST_MSAny:
+      case EST_NoexceptFalse:
+      case EST_DependentNoexcept:
+      case EST_Unevaluated:
+      case EST_Uninstantiated:
+      case EST_Unparsed:
+        S.Diag(attr.getLoc(), diag::warn_nothrow_attribute_ignored);
+        break;
+      }
+      return true;
+    }
+
+    type = unwrapped.wrap(
+        S, S.Context
+               .getFunctionTypeWithExceptionSpec(
+                   QualType{Proto, 0},
+                   FunctionProtoType::ExceptionSpecInfo{EST_NoThrow})
+               ->getAs<FunctionType>());
+    return true;
+  }
+
   // Delay if the type didn't work out to a function.
   if (!unwrapped.isFunctionType()) return false;