Improve memory handling of the Proxy contract

[facuspagnuolo]

Some issues here:

• the free memory pointer is never updated
• we are using ptr again here without re-reading it.

[frangio]

Within the assembly block the free pointer should be guaranteed to not change, unless we explicitly do otherwise. Unfortunately I don't think we will find this documented, but it's the expected behavior of inline assembly in any programming language.

The delegated call uses a different memory space.

[facuspagnuolo]

Agree, unfortunately I didn't find that in the official documentation too. But there is one inline assembly example showing how the the free memory pointer is updated. And there is another here showing how a memory allocate works updating the free memory pointer too.

However, there is no formal explanation whether it should be managed that way or not. Given the delegatecall uses a different memory space, I think we can just add a comment saying why there is no need to update the pointer

[alcuadrado]

Neither updating the free memory pointer nor using it is needed. Using 0 instead of ptr is safe because:

1. Nothing can happen after the inline assembly block. It always run return or revert, and both of them stop the evm execution. So the ABI doesn't need to be followed after the assembly block.

2. The proxied contract uses a new address space after the delegatecall, so we can do whatever we want with the proxy's one.

[Eenae]

Proper resource accounting is just a good programming style. It'll help you mitigate potential errors in future. Consider this potential case: someone is adding extra code before delegatecall, possibly with extra memory consumption, effectively overwriting delegatecall arguments.

Above said is no longer relevant in case of using memory pointer 0x0 (skipping solidity "allocator" altogether).