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Merge emit_small_memcpy and emit_small_memmove (#1301)

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* Merge emit_small_memcpy and emit_small_memmove

* Fix typo
This commit is contained in:
bjorn3
2020-02-14 23:44:40 +01:00
committed by GitHub
parent 18b40d1101
commit 45cc95e60e
1 changed files with 27 additions and 58 deletions
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81
cranelift/frontend/src/frontend.rs
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@@ -1,7 +1,6 @@
//! A frontend for building Cranelift IR from other languages.
use crate::ssa::{SSABlock, SSABuilder, SideEffects};
use crate::variable::Variable;
use alloc::vec::Vec;
use cranelift_codegen::cursor::{Cursor, FuncCursor};
use cranelift_codegen::entity::{EntitySet, SecondaryMap};
use cranelift_codegen::ir;
@@ -626,8 +625,15 @@ impl<'a> FunctionBuilder<'a> {
self.ins().call(libc_memcpy, &[dest, src, size]);
}
/// Optimised memcpy for small copies.
pub fn emit_small_memcpy(
/// Optimised memcpy or memmove for small copies.
///
/// # Codegen safety
///
/// The following properties must hold to prevent UB:
///
/// * `src_align` and `dest_align` are an upper-bound on the alignment of `src` respectively `dest`.
/// * If `non_overlapping` is true, then this must be correct.
pub fn emit_small_memory_copy(
&mut self,
config: TargetFrontendConfig,
dest: Value,
@@ -635,6 +641,7 @@ impl<'a> FunctionBuilder<'a> {
size: u64,
dest_align: u8,
src_align: u8,
non_overlapping: bool,
) {
// Currently the result of guess work, not actual profiling.
const THRESHOLD: u64 = 4;
@@ -663,16 +670,27 @@ impl<'a> FunctionBuilder<'a> {
if load_and_store_amount > THRESHOLD {
let size_value = self.ins().iconst(config.pointer_type(), size as i64);
if non_overlapping {
self.call_memcpy(config, dest, src, size_value);
} else {
self.call_memmove(config, dest, src, size_value);
}
return;
}
let mut flags = MemFlags::new();
flags.set_aligned();
for i in 0..load_and_store_amount {
// Load all of the memory first. This is necessary in case `dest` overlaps.
// It can also improve performance a bit.
let registers: smallvec::SmallVec<[_; THRESHOLD as usize]> = (0..load_and_store_amount)
.map(|i| {
let offset = (access_size * i) as i32;
let value = self.ins().load(int_type, flags, src, offset);
(self.ins().load(int_type, flags, src, offset), offset)
})
.collect();
for (value, offset) in registers {
self.ins().store(flags, value, dest, offset);
}
}
@@ -798,55 +816,6 @@ impl<'a> FunctionBuilder<'a> {
self.ins().call(libc_memmove, &[dest, source, size]);
}
/// Optimised memmove for small moves.
pub fn emit_small_memmove(
&mut self,
config: TargetFrontendConfig,
dest: Value,
src: Value,
size: u64,
dest_align: u8,
src_align: u8,
) {
// Currently the result of guess work, not actual profiling.
const THRESHOLD: u64 = 4;
let access_size = greatest_divisible_power_of_two(size);
assert!(
access_size.is_power_of_two(),
"`size` is not a power of two"
);
assert!(
access_size >= u64::from(::core::cmp::min(src_align, dest_align)),
"`size` is smaller than `dest` and `src`'s alignment value."
);
let load_and_store_amount = size / access_size;
if load_and_store_amount > THRESHOLD {
let size_value = self.ins().iconst(config.pointer_type(), size as i64);
self.call_memmove(config, dest, src, size_value);
return;
}
let mut flags = MemFlags::new();
flags.set_aligned();
// Load all of the memory first in case `dest` overlaps.
let registers: Vec<_> = (0..load_and_store_amount)
.map(|i| {
let offset = (access_size * i) as i32;
(
self.ins().load(config.pointer_type(), flags, src, offset),
offset,
)
})
.collect();
for (value, offset) in registers {
self.ins().store(flags, value, dest, offset);
}
}
}
fn greatest_divisible_power_of_two(size: u64) -> u64 {
@@ -1104,7 +1073,7 @@ block0:
let src = builder.use_var(x);
let dest = builder.use_var(y);
let size = 8;
builder.emit_small_memcpy(target.frontend_config(), dest, src, size, 8, 8);
builder.emit_small_memory_copy(target.frontend_config(), dest, src, size, 8, 8, true);
builder.ins().return_(&[dest]);
builder.seal_all_blocks();
@@ -1161,7 +1130,7 @@ block0:
let src = builder.use_var(x);
let dest = builder.use_var(y);
let size = 8192;
builder.emit_small_memcpy(target.frontend_config(), dest, src, size, 8, 8);
builder.emit_small_memory_copy(target.frontend_config(), dest, src, size, 8, 8, true);
builder.ins().return_(&[dest]);
builder.seal_all_blocks();