Reduced gas cost for call to self

EIPS/eip-1380.md

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+---
+eip: 1380
+title: Reduced gas cost for call to self
+author: Alex Beregszaszi (@axic), Jacques Wagener (@jacqueswww)
+discussions-to: https://ethereum-magicians.org/t/eip-1380-reduced-gas-cost-for-call-to-self/1242
+status: Draft
+type: Standards Track
+category: Core
+created: 2018-08-31
+requires: 150
+---
+
+## Abstract
+Reduce the gas cost for call instructions, when the goal is to run a new instance of the currently loaded contract.
+
+## Motivation
+The current gas cost of 700 for all call types (`CALL`, `DELEGATECALL`, `CALLCODE` and `STATICCALL`) does not take into account that a call to a contract itself
+does not need to perform additional I/O operations, because the current contract code has already been loaded into memory.
+
+Reducing the call-to-self gas cost would greatly benefit smart contract languages, such as Solidity and Vyper, who would then be able to utilise `CALL` instead
+of `JUMP` opcodes for internal function calls. While languages can already utilise `CALL` for internal function calls, they are discouraged to do so due to the
+gas costs associated with it.
+
+Using `JUMP` comes at a considerable cost in complexity to the implementation of a smart contract language and/or compiler. The context (including stack and memory)
+must be swapped in and out of the calling functions context. A desired feature is having *pure* functions, which do not modify the state of memory, and realising
+them through `JUMP` requires a bigger effort from the compiler as opposed to being able to use `CALL`s.
+
+Using call-to-self provides the guarentee that when making an internal call the function can rely on a clear reset state of memory or context, benefiting both
+contract writers and contract consumers against potentially undetetected edge cases were memory could poison the context of the internal function.
+
+Because of the `JUMP` usage for internal functions a smart contract languages are also at risk of reaching the stack depth limit considerbly faster, if nested
+function calls with many in and/or outputs are required.
+
+Reducing the gas cost, and thereby incentivising of using call-to-self instead of `JUMP`s for the internal function implementation will also benefit static
+analyzers and tracers.
+
+## Specification
+If `block.number >= FORK_BLKNUM`, then decrease the cost of `CALL`, `DELEGATECALL`, `CALLCODE` and `STATICCALL` from 700 to 40,
+if and only if, the destination address of the call equals to the address of the caller.
+
+## Rationale
+EIP150 has increased the cost of these instructions from 40 to 700 to more fairly charge for loading new contracts from disk, e.g. to reflect the I/O charge more closely.
+By assuming that 660 is the cost of loading a contract from disk, one can assume that the original 40 gas is a fair cost of creating a new VM instance of an already loaded contract code.
+
+## Backwards Compatibility
+This should pose no risk to backwards compatibility. Currently existing contracts should not notice the difference, just see cheaper execution.
+With EIP150 contract (and language) developers had a lesson that relying on strict gas costs is not feasible as costs may change.
+The impact of this EIP is even less that of EIP150 because the costs are changing downwards and not upwards.
+
+## Test Cases
+TBA
+
+## Implementation
+TBA
+
+## Copyright
+Copyright and related rights waived via [CC0](https://creativecommons.org/publicdomain/zero/1.0/).