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Optimize away unnecessary jump right before return

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This commit is contained in:
Brendan Hansknecht 2021-09-21 00:14:13 -07:00
parent 54e2792b12
commit 1fb0c8043f
2 changed files with 45 additions and 7 deletions
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51
compiler/gen_dev/src/generic64/mod.rs
View file

@ -340,20 +340,48 @@ impl<
let setup_offset = out.len();
// Deal with jumps to the return address.
let ret_offset = self.buf.len();
let old_relocs = std::mem::replace(&mut self.relocs, bumpalo::vec![in self.env.arena]);
// Check if their is an unnessary jump to return right at the end of the function.
let mut end_jmp_size = 0;
for reloc in old_relocs
.iter()
.filter(|reloc| matches!(reloc, Relocation::JmpToReturn { .. }))
{
if let Relocation::JmpToReturn {
inst_loc,
inst_size,
..
} = reloc
{
if *inst_loc as usize + *inst_size as usize == self.buf.len() {
end_jmp_size = *inst_size as usize;
break;
}
}
}
// Update jumps to returns.
let ret_offset = self.buf.len() - end_jmp_size;
let mut tmp = bumpalo::vec![in self.env.arena];
for reloc in old_relocs
.iter()
.filter(|reloc| matches!(reloc, Relocation::JmpToReturn { .. }))
{
if let Relocation::JmpToReturn { inst_loc, offset } = reloc {
self.update_jmp_imm32_offset(&mut tmp, *inst_loc, *offset, ret_offset as u64);
if let Relocation::JmpToReturn {
inst_loc,
inst_size,
offset,
} = reloc
{
if *inst_loc as usize + *inst_size as usize != self.buf.len() {
self.update_jmp_imm32_offset(&mut tmp, *inst_loc, *offset, ret_offset as u64);
}
}
}
// Add function body.
out.extend(&self.buf);
out.extend(&self.buf[..self.buf.len() - end_jmp_size]);
// Cleanup stack.
CC::cleanup_stack(
@ -606,8 +634,13 @@ impl<
offset: offset + sub_func_offset,
name,
},
Relocation::JmpToReturn { inst_loc, offset } => Relocation::JmpToReturn {
Relocation::JmpToReturn {
inst_loc,
inst_size,
offset,
} => Relocation::JmpToReturn {
inst_loc: inst_loc + sub_func_offset,
inst_size,
offset: offset + sub_func_offset,
},
}));
@ -1017,8 +1050,11 @@ impl<
}
let inst_loc = self.buf.len() as u64;
let offset = ASM::jmp_imm32(&mut self.buf, 0x1234_5678) as u64;
self.relocs
.push(Relocation::JmpToReturn { inst_loc, offset });
self.relocs.push(Relocation::JmpToReturn {
inst_loc,
inst_size: self.buf.len() as u64 - inst_loc,
offset,
});
Ok(())
}
}
@ -1384,6 +1420,7 @@ impl<
Ok(())
}
// Updates a jump instruction to a new offset and returns the number of bytes written.
fn update_jmp_imm32_offset(
&mut self,
tmp: &mut Vec<'a, u8>,

1
compiler/gen_dev/src/lib.rs
View file

@ -48,6 +48,7 @@ pub enum Relocation {
},
JmpToReturn {
inst_loc: u64,
inst_size: u64,
offset: u64,
},
}