[foreign-memaccess] RFR 8225172: Add way to create deref VarHandles without using the Layout API

[Maurizio Cimadamore]

On 13/06/2019 16:40, Jorn Vernee wrote:
> Updated webrev: 
> https://cr.openjdk.java.net/~jvernee/panama/webrevs/8225172/webrev.04/
>
> The sizeOf(Class) call was also implicitly doing a carrier type check, 
> so I'm now doing that explicitly in 
> MemoryAccessVarHandles::dereferenceVarHandle and 
> LayoutPathImpl::dereferenceVarHandle instead, and added a test case 
> for this as well. 

Looks nice...

Of these two checks:

if (!carrier.isPrimitive() || carrier == void.class || carrier == 
boolean.class) {
+            throw new IllegalArgumentException("Illegal carrier: " + 
carrier.getSimpleName());
+        }
+
+        if (Wrapper.forPrimitiveType(carrier).bitWidth() != 
layout.bitsSize()) {
+            throw new IllegalArgumentException("Invalid carrier: " + 
carrier + ", for layout " + layout);
+        }


The former seems redundant. BitWidth of void is zero, and the 
ValueLayout API throws IAE if size is 0.

So I would rewrite as this:

Wrapper wrapper = Wrapper.forPrimitiveType(carrier);
if (wrapper == null || //not a primitive
     wrapper.bitWidth() != layout.bitSize()) { //incompatible sizes (or 
void carrier!)
   throw new IllegalArgumentException(...)
}

And, again, if you check the carrier both in MemoryAccessVarHandles, and 
in LayoutPath, I don't see the need for checking it in VarHandles.

Maurizio