Make ASTContext::getDeclAlign return the correct alignment for FunctionDecls

[ahatanak]

Summary

This patch silences an incorrect warning that is issued when a function pointer is cast to another function pointer type. The warning gets issued because alignments of the source and destination do not match in Sema::CheckCastAlign, which happens because ASTContext::getTypeInfoImpl and ASTContext::getDeclAlign return different values for functions (the former returns 4 while the latter returns 1).

[ahatanak]

Call getTypeInfoImpl from getDeclAlign to get the alignment of functions.

[arphaman]

Does this happen with blocks as well?

[ahatanak]

This doesn't happen for objective-c block pointers. Sema::CheckCastAlign returns early when the type isn't a PointerType (BlockPointerType isn't a subclass of PointerType).

[ahatanak]

ping

[ahatanak]

ping

[arphaman]

Thanks. LGTM, I think the patch makes sense.

lib/AST/ASTContext.cpp

if (const FieldDecl *Field = dyn_cast<FieldDecl>(VD)) {
           // which means we get to do this crazy thing instead of Euclid's.
           uint64_t LowBitOfOffset = Offset & (~Offset + 1);
           if (LowBitOfOffset < FieldAlign)
             FieldAlign = static_cast<unsigned>(LowBitOfOffset);
         }
 
         Align = std::min(Align, FieldAlign);
       }
-    }
+    } else if (isa<FunctionDecl>(VD))
+      // GCC extension: alignment of functions is 32 bits
+      Align = 32;
   }
 
   return toCharUnitsFromBits(Align);
 }
 
 // getTypeInfoDataSizeInChars - Return the size of a type, in
 // chars. If the type is a record, its data size is returned.  This is
 // the size of the memcpy that's performed when assigning this type

test/Sema/warn-cast-align.c

 };
 
 void test4() {
   struct S s;
   int *i = (int *)s.a;
   i = (int *)&s.s0;
   i = (int *)a;
 }
+
+// No warnings.
+typedef int (*FnTy)(void);
+unsigned int func5(void);
+
+FnTy test5(void) {
+  return (FnTy)&func5;
+}