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Use -Clinker-plugin-lto flag during Wasm build #358

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ascjones merged 2 commits into from
Nov 16, 2021
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Use -Clinker-plugin-lto flag during Wasm build #358

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ed72e75
`-Clinker-plugin-lto` reduced the size of my contract
xgreenx Nov 10, 2021
86a10ca
Compiler will use `-Clinker-plugin-lto` if `lto` is enabled
xgreenx Nov 11, 2021
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2 changes: 1 addition & 1 deletion src/cmd/build.rs
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Expand Up @@ -249,7 +249,7 @@ fn exec_cargo_for_wasm_target(
// Currently will override user defined RUSTFLAGS from .cargo/config. See https://github.com/paritytech/cargo-contract/issues/98.
std::env::set_var(
"RUSTFLAGS",
"-C link-arg=-zstack-size=65536 -C link-arg=--import-memory",
"-C link-arg=-zstack-size=65536 -C link-arg=--import-memory -Clto -Clinker-plugin-lto",
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@ascjones ascjones Nov 11, 2021

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I believe the -Clto will override the release profile which we automatically append/merge to the contract's Cargo.toml. See https://github.com/paritytech/cargo-contract/blob/a8c8589798c05468b41e8125b6c5c3c1194178b6/src/workspace/profile.rs#L22.

I think we might still need to pass Clinker-plugin-lto directly as an argument, but AFAIU it seems dependent upon -Clto which is configurable from the [profile.release]

The philosophy we have followed so far is that we should provide sensible defaults for these values, but also allow the user to override them, because the same hardcoded flags might now always produce the optimal contract size for all contracts.

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@xgreenx xgreenx Nov 11, 2021

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What do you think if we will add it automatically here if lto is on?=)

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@ascjones ascjones Nov 11, 2021

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Clinker-plugin-lto is not a profile setting https://doc.rust-lang.org/cargo/reference/profiles.html.

What effect does just having Clto on its own have on the size?

Anyway if this flag is providing such big gains, and doesn't harm any of the other Lto options then we can possibly hardcode it.

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@xgreenx xgreenx Nov 11, 2021 •
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For example that contract takes space:
Without -Clto and -Clinker-plugin-lto: Original wasm size: 100.5K, Optimized: 47.9K
With -Clto: Original wasm size: 68.6K, Optimized: 31.9K
With -Clto and -Clinker-plugin-lto: Original wasm size: 67.2K, Optimized: 31.0K

I tried it on contracts from that folder and it causes a positive effect for all of them(but all of them has a heavy logic, except reentrancy. For reentrancy it causes a low impact there).

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@xgreenx xgreenx Nov 11, 2021

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I did measurements for reentrancy. Also, I removed explicit -Clto because it causes a compilation error if it is disabled or not aplieable. I tested compiler will use -Clinker-plugin-lto if he can.

flipper:
Original wasm size: 38.9K, Optimized: 12.5K
Original wasm size: 24.4K, Optimized: 4.5K
Original wasm size: 24.1K, Optimized: 4.2K

flip_on_me:
Original wasm size: 33.8K, Optimized: 10.2K
Original wasm size: 21.5K, Optimized: 2.6K
Original wasm size: 21.2K, Optimized: 2.3K

);

let cargo_build = |manifest_path: &ManifestPath| {
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