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movs: fast path for unaligned src/dst

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This commit is contained in:
Fabian 2022-11-10 16:40:13 -06:00
parent 685c39177f
commit 756ce66888
2 changed files with 50 additions and 24 deletions
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5
src/rust/cpu/memory.rs
View file

@ -228,8 +228,9 @@ pub unsafe fn memset_no_mmap_or_dirty_check(addr: u32, value: u8, count: u32) {
}
pub unsafe fn memcpy_no_mmap_or_dirty_check(src_addr: u32, dst_addr: u32, count: u32) {
dbg_assert!(u32::max(src_addr, dst_addr) - u32::min(src_addr, dst_addr) >= count);
ptr::copy_nonoverlapping(
dbg_assert!(src_addr < *memory_size);
dbg_assert!(dst_addr < *memory_size);
ptr::copy(
mem8.offset(src_addr as isize),
mem8.offset(dst_addr as isize),
count as usize,

69
src/rust/cpu/string.rs
View file

@ -34,7 +34,7 @@ fn count_until_end_of_page(direction: i32, size: i32, addr: u32) -> u32 {
}) as u32
}
#[derive(Copy, Clone)]
#[derive(Copy, Clone, PartialEq)]
enum Instruction {
Movs,
Lods,
@ -135,7 +135,9 @@ unsafe fn string_instruction(
};
let is_aligned = (ds + src) & (size_bytes - 1) == 0 && (es + dst) & (size_bytes - 1) == 0;
let mut rep_fast = is_aligned
// unaligned movs is properly handled in the fast path
let mut rep_fast = (instruction == Instruction::Movs || is_aligned)
&& is_asize_32 // 16-bit address wraparound
&& match rep {
Rep::NZ | Rep::Z => true,
@ -145,7 +147,9 @@ unsafe fn string_instruction(
let mut phys_dst = 0;
let mut phys_src = 0;
let mut skip_dirty_page = false;
let mut movs_into_svga_lfb = false;
let mut movs_reenter_fast_path = false;
if rep_fast {
match instruction {
@ -184,10 +188,27 @@ unsafe fn string_instruction(
match instruction {
Instruction::Movs => {
// note: This check is also valid for both direction == 1 and direction == -1
let overlap = u32::max(phys_src, phys_dst) - u32::min(phys_src, phys_dst)
< count * size_bytes as u32;
rep_fast = rep_fast && !overlap;
let c = count * size_bytes as u32;
let overlap_interferes = if phys_src < phys_dst {
// backward moves may overlap at the front of the destination string
phys_dst - phys_src < c && direction == 1
}
else if phys_src > phys_dst {
// forward moves may overlap at the front of the source string
phys_src - phys_dst < c && direction == -1
}
else {
false
};
rep_fast = rep_fast && !overlap_interferes;
// In case the following page-boundary check fails, re-enter instruction after
// one iteration of the slow path
movs_reenter_fast_path = rep_fast;
rep_fast = rep_fast
&& (phys_src & 0xFFF <= 0x1000 - size_bytes as u32)
&& (phys_dst & 0xFFF <= 0x1000 - size_bytes as u32);
},
_ => {},
}
@ -419,23 +440,27 @@ unsafe fn string_instruction(
_ => {},
};
count -= 1;
let finished = match rep {
Rep::Z | Rep::NZ => {
let rep_cmp = match (rep, instruction) {
(Rep::Z, Instruction::Cmps) => src_val == dst_val,
(Rep::Z, Instruction::Scas) => src_val == dst_val,
(Rep::NZ, Instruction::Cmps) => src_val != dst_val,
(Rep::NZ, Instruction::Scas) => src_val != dst_val,
_ => true,
};
count -= 1;
if count != 0 && rep_cmp {
//*instruction_pointer = *previous_ip
false
}
else {
true
}
Rep::Z | Rep::NZ => match (rep, instruction) {
(Rep::Z, Instruction::Cmps) => src_val != dst_val || count == 0,
(Rep::Z, Instruction::Scas) => src_val != dst_val || count == 0,
(Rep::NZ, Instruction::Cmps) => src_val == dst_val || count == 0,
(Rep::NZ, Instruction::Scas) => src_val == dst_val || count == 0,
(Rep::NZ | Rep::Z, Instruction::Movs) => {
if count == 0 {
true
}
else if movs_reenter_fast_path {
*instruction_pointer = *previous_ip;
true
}
else {
false
}
},
_ => count == 0,
},
Rep::None => true,
};