Feature Guide for Yul
September 6, 2021 · View on GitHub
Feature Guide for Yul
Introduction
In this guide, we will list all Yul language features and briefly summarize the current status and limitations about SOLL implementation.
Grammar
Our parser already covered most parts of valid grammar base on 0.6.6. Your can use soll -lang=Yul -action=ASTDump ...*.yul verify parser functional behavior.
If you want to execute ewasm compiled from Yul, refer to the DevGuide.
Supported by SOLL
Grammar
- Recognize Yul object structure.
- Statement
- Block
- FunctionDefinition
- VariableDeclaration
- Assignment
- Switch
- If
- ForLoop
- BreakContinue
- FunctionCall
- Leave
- Basic arithmetical, compare and storage/memory access built-in functions.
- Partial state, object and misc built-in functions.
Additional Functions
| Instruction | Explanation |
|---|---|
| *datasize(x) [See below] | - |
| *dataoffset(x) [See below] | - |
| datacopy(t, f, l) | - |
datasizeanddataoffsetin our implementation have a constraint. They both couldn't be used apply on object itself.
EVM Dialect
Opcodes marked with - do not return a result and all others return exactly one value.
Opcodes marked with F, H, B, C or I are present since Frontier, Homestead, Byzantium, Constantinople or Istanbul, respectively.
| Instruction | Explanation | ||
|---|---|---|---|
| stop() | - | F | stop execution, identical to return(0, 0) |
| add(x, y) | F | x + y | |
| sub(x, y) | F | x - y | |
| mul(x, y) | F | x * y | |
| div(x, y) | F | x / y or 0 if y == 0 | |
| sdiv(x, y) | F | x / y, for signed numbers in two’s complement, 0 if y == 0 | |
| mod(x, y) | F | x % y, 0 if y == 0 | |
| exp(x, y) | F | x to the power of y | |
| not(x) | F | bitwise “not” of x (every bit of x is negated) | |
| lt(x, y) | F | 1 if x < y, 0 otherwise | |
| gt(x, y) | F | 1 if x > y, 0 otherwise | |
| slt(x, y) | F | 1 if x < y, 0 otherwise, for signed numbers in two’s complement | |
| sgt(x, y) | F | 1 if x > y, 0 otherwise, for signed numbers in two’s complement | |
| eq(x, y) | F | 1 if x == y, 0 otherwise | |
| iszero(x) | F | 1 if x == 0, 0 otherwise | |
| and(x, y) | F | bitwise “and” of x and y | |
| or(x, y) | F | bitwise “or” of x and y | |
| xor(x, y) | F | bitwise “xor” of x and y | |
| shl(x, y) | C | logical shift left y by x bits | |
| shr(x, y) | C | logical shift right y by x bits | |
| sar(x, y) | C | signed arithmetic shift right y by x bits | |
| addmod(x, y, m) | F | (x + y) % m with arbitrary precision arithmetic, 0 if m == 0 | |
| mulmod(x, y, m) | F | (x * y) % m with arbitrary precision arithmetic, 0 if m == 0 | |
| signextend(i, x) | F | sign extend from (i*8+7)th bit counting from least significant | |
| keccak256(p, n) | F | keccak(mem[p…(p+n))) | |
| mload(p) | F | mem[p…(p+32)) | |
| mstore(p, v) | - | F | mem[p…(p+32)) := v |
| mstore8(p, v) | - | F | mem[p] := v & 0xff (only modifies a single byte) |
| sload(p) | F | storage[p] | |
| sstore(p, v) | - | F | storage[p] := v |
| msize() | F | size of memory, i.e. largest accessed memory index | |
| gas() | F | gas still available to execution | |
| caller() | F | call sender (excluding delegatecall) | |
| callvalue() | F | wei sent together with the current call | |
| calldataload(p) | F | call data starting from position p (32 bytes) | |
| calldatasize() | F | size of call data in bytes | |
| codecopy(t, f, s) | - | F | copy s bytes from code at position f to mem at position t |
| return(p, s) | - | F | end execution, return data mem[p…(p+s)) |
| revert(p, s) | - | B | end execution, revert state changes, return data mem[p…(p+s)) |
| log0(p, s) | - | F | log without topics and data mem[p…(p+s)) |
| log1(p, s, t1) | - | F | log with topic t1 and data mem[p…(p+s)) |
| log2(p, s, t1, t2) | - | F | log with topics t1, t2 and data mem[p…(p+s)) |
| log3(p, s, t1, t2, t3) | - | F | log with topics t1, t2, t3 and data mem[p…(p+s)) |
| log4(p, s, t1, t2, t3, t4) | - | F | log with topics t1, t2, t3, t4 and data mem[p…(p+s)) |
| origin() | F | transaction sender | |
| gasprice() | F | gas price of the transaction | |
| coinbase() | F | current mining beneficiary | |
| timestamp() | F | timestamp of the current block in seconds since the epoch | |
| number() | F | current block number | |
| difficulty() | F | difficulty of the current block | |
| gaslimit() | F | block gas limit of the current block | |
| address() | F | address of the current contract / execution context | |
| balance(a) | F | wei balance at address a | |
| selfbalance() | I | equivalent to balance(address()), but cheaper | |
| calldatacopy(t, f, s) | - | F | copy s bytes from calldata at position f to mem at position t |
| codesize() | F | size of the code of the current contract / execution context | |
| extcodesize(a) | F | size of the code at address a | |
| extcodecopy(a, t, f, s) | - | F | like codecopy(t, f, s) but take code at address a |
| returndatasize() | B | size of the last returndata | |
| returndatacopy(t, f, s) | - | B | copy s bytes from returndata at position f to mem at position t |
| smod(x, y) | F | x % y, for signed numbers in two’s complement, 0 if y == 0 | |
| blockhash(b) | F | hash of block nr b - only for last 256 blocks excluding current | |
| byte(n, x) | F | nth byte of x, where the most significant byte is the 0th byte | |
| pop(x) | - | F | discard value x |
| extcodehash(a) | C | code hash of address a | |
| create(v, p, n) | F | create new contract with code mem[p…(p+n)) and send v wei and return the new address | |
| call(g, a, v, in, insize, out, outsize) | F | call contract at address a with input mem[in…(in+insize)) providing g gas and v wei and output area mem[out…(out+outsize)) returning 0 on error (eg. out of gas) and 1 on success See more | |
| callcode(g, a, v, in, insize, out, outsize) | F | identical to call but only use the code from a and stay in the context of the current contract otherwise See more | |
| delegatecall(g, a, in, insize, out, outsize) | H | identical to callcode but also keep caller and callvalue See more | |
| staticcall(g, a, in, insize, out, outsize) | B | identical to call(g, a, 0, in, insize, out, outsize) but do not allow state modifications See more | |
| selfdestruct(a) | - | F | end execution, destroy current contract and send funds to a |
| invalid() | - | F | end execution with invalid instruction |
| create2(v, p, n, s) | C | create new contract with code mem[p…(p+n)) at address keccak256(0xff . this . s . keccak256(mem[p…(p+n))) and send v wei and return the new address, where 0xff is a 1 byte value, this is the current contract’s address as a 20 byte value and s is a big-endian 256-bit value | |
| chainid() | I | ID of the executing chain (EIP 1344) |
Future works
Below will describe some under implement language features.
Features
These features are not supported yet.
- calculate
dataoffsetto the object itself - calculate
datasizeto the object itself - directly convert string to bool or int
Identifier : TypeName(e.g.var:u256)
Grammar
| feature | item | example |
|---|---|---|
| Statement | Switch with string literal | case "" |
Additional Functions
Some newly announced functions after v0.7.0 breaking update.
| Instruction | Explanation |
|---|---|
| setimmutable | - |
| loadimmutable | - |
| linkersymbol("fq_library_name") | - |