# Description
Compilation times for resolc were significantly slower than solc when:
* Multiple files were included in the JSON input file via
`--standard-json`
* And none of the files requested code generation
* (If only a subset of files requested code generation, both resolc and
solc were very slow)
Reason:
* Resolc unconditionally generated bytecode for all contracts, even if
not requested.
* When compiling to PolkaVM bytecode, we need to pass additional flags
(e.g. `irOptimized`) to solc. If these flags were not explicitly
requested, resolc also added these to the requested output since PolkaVM
bytecode was always generated.
## Breaking Changes
The following changes are breaking, but fix the semantics to match its
intended behavior:
* Compiling with `--standard-json` now compiles to PolkaVM bytecode
***only*** for the contracts explicitly requested in the
`outputSelection`.
* Compiling with `--standard-json` now outputs ***only*** the explicitly
requested output (e.g. `evm.assembly`, `evm.bytecode`, `ast`, etc.).
```jsonc
// Example:
{
"settings": {
// ...
"outputSelection": {
"src/common/GasService.sol": {
// Contracts in this file will generate bytecode.
// Only these fields of the JSON output selection will be in the `contracts` output.
"*": ["abi", "evm.methodIdentifiers", "metadata", "evm.bytecode"],
// Only this field of the JSON output selection will be in the `sources` output.
"": ["ast"]
},
"src/common/Gateway.sol": {
// No contracts in this file will generate bytecode.
"*": ["abi", "evm.methodIdentifiers", "metadata"],
// No `ast` will be in the `sources` output (only the automatically added `id`,
// similar to solc as this is not a configurable output selection).
"": []
},
}
}
}
```
## Performance Improvements
When e.g. the standard JSON input file includes multiple files and
requests output for every contract as per this setting:
```jsonc
{
"settings": {
// ...
"optimizer": { "enabled": true, "runs": 1 },
"viaIR": true,
"outputSelection": {
"src/common/GasService.sol": {
"*": ["abi", "evm.methodIdentifiers", "metadata", "evm.bytecode"],
},
// Rest of files..
}
}
}
```
The differences in compilation times depending on whether `evm.bytecode`
is selected in every file, one file, or no files can be seen below:
| Solc Optimizer (runs=1) | ViaIR | Request `abi`,
`evm.methodIdentifiers`, `metadata` | Request `evm.bytecode` | resolc
before | resolc after | solc v0.8.33 |
|:-----------------------:|:-----:|:---------:|:---------:|:-------------:|:------------:|:----------:|
| ✅ | ✅ | All files | All files | `~14.5s` | `~14.5s` | `~13.5s` |
| ✅ | ✅ | All files | One file | `~14.5s` | `~450ms` | `~13.5s` |
| ✅ | ✅ | All files | No files | `~14.5s` | `~390ms` | `~350ms` |
**Observations:**
* `resolc before` is roughly the same no matter the request
* This is due to unconditionally generating bytecode
* When not requesting bytecode for any contracts:
* `resolc after` now compiles in ~390ms (vs ~14.5s), similar to `solc`
* Neither `solc` nor `resolc after` generates bytecode when none of the
contracts request it
* When requesting bytecode for all contracts in _only one_ file:
* `resolc after` now compiles in ~450ms (vs ~14.5s)
* `solc` still compiles in the same time as when requesting bytecode for
all contracts in all files
* This is something they have tried to improve (see
[Solidity#15373](https://github.com/argotorg/solidity/issues/15373) and
[Solidity#15615](https://github.com/argotorg/solidity/issues/15615)),
and the intended behavior seems to now be that bytecode should only be
generated when explicitly requested for each contract.
* Even though PRs have merged to try to fix it, their issue seems to
persist as of v0.8.33.
# Open Questions
* Foundry:
* [x] Pruning of the AST:
* Just saw [this past
commit](https://github.com/paritytech/revive/pull/385) to not prune the
AST for Foundry compatibility.
* Can Foundry not explicitly request `"": "ast"`?
* **Answer:**
* Pruning the AST when not requested should be fine, as long as Foundry
explicitly requests it when needed.
* Will be tested by Foundry maintainer.
# Review Notes
Changes in `docs/` (~25 files) can be skipped as they are automatically
updated after adding content to `book/` and rebuilding it.
# Resolved Issues
Closes#326
---------
Co-authored-by: xermicus <cyrill@parity.io>
Fixes https://github.com/paritytech/contract-issues/issues/149
A few test cases from v2-periphery-polkadot are hitting the PVM stack
limit when the contracts are compiled using resolc version 0.5.0. The
same tests pass if the contracts are compiled with a resolc version that
includes commit:
https://github.com/paritytech/revive/commit/878ca91689b99220f7ffd40df760613b7314de86.
After a brief discussion with @xermicus, we propose to set the default
PolkaVM stack and heap size values to 128KB, since we have already
encountered tests that hit the stack size limit and, without real world
data, it is difficult to determine the optimal values.
