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Use a SmallVec for ABIArgSlots (#4586)

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These are always length 1 for Wasm benchmarks.

<h3>Sightglass Benchmark Results</h3>

```
compilation :: nanoseconds :: benchmarks/spidermonkey/benchmark.wasm

  Δ = 328624015.86 ± 40274677.93 (confidence = 99%)

  main.so is 0.88x to 0.91x faster than slots-smallvec.so!
  slots-smallvec.so is 1.10x to 1.13x faster than main.so!

  [3070752447 3203778792.55 3446269274] main.so
  [2503544039 2875154776.69 3197966713] slots-smallvec.so

compilation :: nanoseconds :: benchmarks/pulldown-cmark/benchmark.wasm

  Δ = 9685705.06 ± 3221286.87 (confidence = 99%)

  main.so is 0.91x to 0.96x faster than slots-smallvec.so!
  slots-smallvec.so is 1.05x to 1.09x faster than main.so!

  [129356493 145594942.79 165038803] main.so
  [118555011 135909237.73 188780619] slots-smallvec.so

compilation :: nanoseconds :: benchmarks/bz2/benchmark.wasm

  No difference in performance.

  [79080493 86757564.46 112649639] main.so
  [78083384 85934125.69 94992743] slots-smallvec.so
```
This commit is contained in:
Nick Fitzgerald
2022-08-02 17:40:36 -07:00
committed by GitHub
parent ab1cf3df2d
commit 55215bbd1e
3 changed files with 10 additions and 5 deletions
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11
cranelift/codegen/src/machinst/abi_impl.rs
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@@ -153,6 +153,11 @@ impl ABIArgSlot {
}
}
/// A vector of `ABIArgSlot`s. Inline capacity for one element because basically
/// 100% of values use one slot. Only `i128`s need multiple slots, and they are
/// super rare (and never happen with Wasm).
pub type ABIArgSlotVec = SmallVec<[ABIArgSlot; 1]>;
/// An ABIArg is composed of one or more parts. This allows for a CLIF-level
/// Value to be passed with its parts in more than one location at the ABI
/// level. For example, a 128-bit integer may be passed in two 64-bit registers,
@@ -169,7 +174,7 @@ pub enum ABIArg {
/// parts used to store a value of this type.
Slots {
/// Slots, one per register part.
slots: Vec<ABIArgSlot>,
slots: ABIArgSlotVec,
/// Purpose of this arg.
purpose: ir::ArgumentPurpose,
},
@@ -206,7 +211,7 @@ impl ABIArg {
purpose: ir::ArgumentPurpose,
) -> ABIArg {
ABIArg::Slots {
slots: vec![ABIArgSlot::Reg { reg, ty, extension }],
slots: smallvec![ABIArgSlot::Reg { reg, ty, extension }],
purpose,
}
}
@@ -219,7 +224,7 @@ impl ABIArg {
purpose: ir::ArgumentPurpose,
) -> ABIArg {
ABIArg::Slots {
slots: vec![ABIArgSlot::Stack {
slots: smallvec![ABIArgSlot::Stack {
offset,
ty,
extension,