### Ipsilon
Hugo de la Cruz Romero -- [github.com/hugo-dc](https://github.com/hugo-dc)
Alex Beregszaszi [github.com/axic](https://github.com/axic)
--
A protocol research team focusing on the EVM. Website: [ipsilon.xyz](https://ipsilon.xyz)
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### EIP-3855: PUSH0 Instruction
- Status: Review
- Considered for inclusion in <br>_Shanghai_ Network Upgrade
---
### Introduction
- Usage of constant value `0`
- Value of zero frequently used by many instructions expecting offsets as inputs.
---
### Introduction
- Examples:
- Opcodes dealing with offsets:
- `CALLDATACOPY`
- `CODECOPY`
- `EXTCODECOPY`
- etc.
- `CALL*`: Setting zeros as return data parameters when the contract prefers using `RETURNDATA*` to retreive the results.
---
### Abstract
- New opcode `PUSH0` with a cost of `2` gas (`base`).
- It is introduced as the instruction number `0x5f`.
|Hex|Name|
|---|----|
|...|... |
|**`0x5f`**| **PUSH0**|
|`0x60`| PUSH1|
|... | PUSHn|
|`0X7f`| PUSH32|
---
### Motivation
- Reduce gas usage and contract code size:
- `PUSH1 00` ~ `60 00`: 400 gas for deployment, 3 gas for runtime.
- `PUSH0` ~ `5f`: 200 gas for deployment, 2 gas for runtime.
---
### Motivation
- Reduce risk of contracts (mis)using instructions as an optimisation measure.
- `PC`
- `MSIZE`
- `CALLDATASIZE`
- `RETURNDATASIZE`
- `CODESIZE`
- `CALLVALUE`
- `SELFBALANCE`
---
### Example
- EIP-2733 (*Withdrawn*)
- If implemented, would have changed the behaviour of `RETURNDATASIZE` such that it may not be guaranteed to be zero at the beginning of the call frame.
---
### Analysis and Findings
---
### Analysis and Findings
- Traced transactions in two different nodes syncing mainnet:
- Geth Node 1: Syncing at block ~8M
- Geth Node 2: Syncing at block ~12M
---
### Analysis and Findings
- Result: Histogram of Opcode usage, with special column for `PUSH1 00` (`PUSH0`):
---
#### General Opcode Usage
---
#### PUSHn Usage
---
#### PUSH1 00
---
#### Other commonly used constants
---
### Commonly used constants
- `0`: solved by `PUSH0`
- `1`: largely used in loops, could be solved by `INC`/`DEC`
- `2`: mostly used by old contracts to emulate shifts
- `31` and `32`: are mostly used by the ABI en/decoder in Solidity
---
### `INC`/`DEC`
- `INC` to increase-by-one the top item, `DEC` to decrease
- Useful for loops, where this is done with `PUSH1 1 ADD`
- Pro: saves 2x200 gas for deployment, and at least costs half runtime
- Con: too much of a CISC direction
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