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cranelift x64: use the LZCNT instruction for Clz when it's available;

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This commit is contained in:
Benjamin Bouvier
2021-01-27 18:44:14 +01:00
parent b1b078e2bc
commit d3acd9a283
4 changed files with 79 additions and 12 deletions
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38
cranelift/codegen/src/isa/x64/inst/emit.rs
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@@ -129,18 +129,20 @@ impl RexFlags {
/// We may need to include one or more legacy prefix bytes before the REX prefix. This enum
/// covers only the small set of possibilities that we actually need.
enum LegacyPrefixes {
/// No prefix bytes
/// No prefix bytes.
None,
/// Operand Size Override -- here, denoting "16-bit operation"
/// Operand Size Override -- here, denoting "16-bit operation".
_66,
/// The Lock prefix
/// The Lock prefix.
_F0,
/// Operand size override and Lock
/// Operand size override and Lock.
_66F0,
/// REPNE, but no specific meaning here -- is just an opcode extension
/// REPNE, but no specific meaning here -- is just an opcode extension.
_F2,
/// REP/REPE, but no specific meaning here -- is just an opcode extension
/// REP/REPE, but no specific meaning here -- is just an opcode extension.
_F3,
/// Operand size override and same effect as F3.
_66F3,
}
impl LegacyPrefixes {
@@ -157,6 +159,10 @@ impl LegacyPrefixes {
}
LegacyPrefixes::_F2 => sink.put1(0xF2),
LegacyPrefixes::_F3 => sink.put1(0xF3),
LegacyPrefixes::_66F3 => {
sink.put1(0x66);
sink.put1(0xF3);
}
LegacyPrefixes::None => (),
}
}
@@ -665,16 +671,28 @@ pub(crate) fn emit(
}
Inst::UnaryRmR { size, op, src, dst } => {
let (prefix, rex_flags) = match size {
2 => (LegacyPrefixes::_66, RexFlags::clear_w()),
4 => (LegacyPrefixes::None, RexFlags::clear_w()),
8 => (LegacyPrefixes::None, RexFlags::set_w()),
let rex_flags = match size {
2 | 4 => RexFlags::clear_w(),
8 => RexFlags::set_w(),
_ => unreachable!(),
};
let prefix = match size {
2 => match op {
UnaryRmROpcode::Bsr | UnaryRmROpcode::Bsf => LegacyPrefixes::_66,
UnaryRmROpcode::Lzcnt => LegacyPrefixes::_66F3,
},
4 | 8 => match op {
UnaryRmROpcode::Bsr | UnaryRmROpcode::Bsf => LegacyPrefixes::None,
UnaryRmROpcode::Lzcnt => LegacyPrefixes::_F3,
},
_ => unreachable!(),
};
let (opcode, num_opcodes) = match op {
UnaryRmROpcode::Bsr => (0x0fbd, 2),
UnaryRmROpcode::Bsf => (0x0fbc, 2),
UnaryRmROpcode::Lzcnt => (0x0fbd, 2),
};
match src {