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machinst x64: emit nop of variable sizes;

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This commit is contained in:
Benjamin Bouvier
2020-10-07 14:05:35 +02:00
parent a470f1e0cd
commit 116acb8dcd
2 changed files with 80 additions and 5 deletions
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83
cranelift/codegen/src/isa/x64/inst/emit.rs
View File

@@ -2720,10 +2720,85 @@ pub(crate) fn emit(
}
Inst::Nop { len } => {
if *len == 0 {
// Nothing to emit.
} else {
unimplemented!("non-zero nop opcodes.");
// These encodings can all be found in Intel's architecture manual, at the NOP
// instruction description.
let mut len = *len;
while len != 0 {
let emitted = u8::min(len, 9);
match emitted {
0 => {}
1 => sink.put1(0x90), // NOP
2 => {
// 66 NOP
sink.put1(0x66);
sink.put1(0x90);
}
3 => {
// NOP [EAX]
sink.put1(0x0F);
sink.put1(0x1F);
sink.put1(0x00);
}
4 => {
// NOP 0(EAX), with 0 a 1-byte immediate.
sink.put1(0x0F);
sink.put1(0x1F);
sink.put1(0x40);
sink.put1(0x00);
}
5 => {
// NOP [EAX, EAX, 1]
sink.put1(0x0F);
sink.put1(0x1F);
sink.put1(0x44);
sink.put1(0x00);
sink.put1(0x00);
}
6 => {
// 66 NOP [EAX, EAX, 1]
sink.put1(0x66);
sink.put1(0x0F);
sink.put1(0x1F);
sink.put1(0x44);
sink.put1(0x00);
sink.put1(0x00);
}
7 => {
// NOP 0[EAX], but 0 is a 4 bytes immediate.
sink.put1(0x0F);
sink.put1(0x1F);
sink.put1(0x80);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
}
8 => {
// NOP 0[EAX, EAX, 1], with 0 a 4 bytes immediate.
sink.put1(0x0F);
sink.put1(0x1F);
sink.put1(0x84);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
}
9 => {
// 66 NOP 0[EAX, EAX, 1], with 0 a 4 bytes immediate.
sink.put1(0x66);
sink.put1(0x0F);
sink.put1(0x1F);
sink.put1(0x84);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
sink.put1(0x00);
}
_ => unreachable!(),
}
len -= emitted;
}
}

2
cranelift/codegen/src/isa/x64/inst/mod.rs
View File

@@ -2487,7 +2487,7 @@ impl MachInst for Inst {
}
fn gen_nop(preferred_size: usize) -> Inst {
Inst::nop(preferred_size as u8)
Inst::nop((preferred_size % 16) as u8)
}
fn maybe_direct_reload(&self, _reg: VirtualReg, _slot: SpillSlot) -> Option<Inst> {