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EbbHeaderBlockData::predecessors: use SmallVec instead of Vec

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Allocations associated with pushes to EbbHeaderBlockData::predecessors account
for 4.9% of all heap allocation (calls) in CL.  This change avoids almost all
of them by changing it to be a SmallVec<[PredBlock; 4]>.  Dynamic instruction
count falls by 0.15%.
This commit is contained in:
Julian Seward
2019-09-07 19:12:42 +02:00
committed by Benjamin Bouvier
parent 955cdd5f83
commit c6a4c60a0f
2 changed files with 9 additions and 4 deletions
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1
cranelift/frontend/Cargo.toml
View File

@@ -15,6 +15,7 @@ cranelift-codegen = { path = "../cranelift-codegen", version = "0.42.0", default
target-lexicon = "0.8.1"
log = { version = "0.4.6", default-features = false }
hashmap_core = { version = "0.1.9", optional = true }
smallvec = { version = "0.6.10" }
[features]
default = ["std"]

12
cranelift/frontend/src/ssa.rs
View File

@@ -16,6 +16,7 @@ use cranelift_codegen::ir::types::{F32, F64};
use cranelift_codegen::ir::{Ebb, Function, Inst, InstBuilder, InstructionData, Type, Value};
use cranelift_codegen::packed_option::PackedOption;
use cranelift_codegen::packed_option::ReservedValue;
use smallvec::SmallVec;
use std::vec::Vec;
/// Structure containing the data relevant the construction of SSA for a given function.
@@ -123,9 +124,11 @@ impl PredBlock {
}
}
type PredBlockSmallVec = SmallVec<[PredBlock; 4]>;
struct EbbHeaderBlockData {
// The predecessors of the Ebb header block, with the block and branch instruction.
predecessors: Vec<PredBlock>,
predecessors: PredBlockSmallVec,
// A ebb header block is sealed if all of its predecessors have been declared.
sealed: bool,
// The ebb which this block is part of.
@@ -366,7 +369,7 @@ impl SSABuilder {
/// Predecessors have to be added with `declare_ebb_predecessor`.
pub fn declare_ebb_header_block(&mut self, ebb: Ebb) -> Block {
let block = self.blocks.push(BlockData::EbbHeader(EbbHeaderBlockData {
predecessors: Vec::new(),
predecessors: PredBlockSmallVec::new(),
sealed: false,
ebb,
undef_variables: Vec::new(),
@@ -587,7 +590,8 @@ impl SSABuilder {
// There is disagreement in the predecessors on which value to use so we have
// to keep the ebb argument. To avoid borrowing `self` for the whole loop,
// temporarily detach the predecessors list and replace it with an empty list.
let mut preds = mem::replace(self.predecessors_mut(dest_ebb), Vec::new());
let mut preds =
mem::replace(self.predecessors_mut(dest_ebb), PredBlockSmallVec::new());
for &mut PredBlock {
block: ref mut pred_block,
branch: ref mut last_inst,
@@ -699,7 +703,7 @@ impl SSABuilder {
}
/// Same as predecessors, but for &mut.
fn predecessors_mut(&mut self, ebb: Ebb) -> &mut Vec<PredBlock> {
fn predecessors_mut(&mut self, ebb: Ebb) -> &mut PredBlockSmallVec {
let block = self.header_block(ebb);
match self.blocks[block] {
BlockData::EbbBody { .. } => panic!("should not happen"),