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Implement branch relaxation.

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Now that we have the legal_encodings iterator, it is simpler to find an
alternative branch encoding with a better range.
This commit is contained in:
Jakob Stoklund Olesen
2017-09-29 12:41:37 -07:00
parent 45888ab84e
commit 50ccd000a9
1 changed files with 25 additions and 2 deletions
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27
lib/cretonne/src/binemit/relaxation.rs
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@@ -80,7 +80,8 @@ pub fn relax_branches(func: &mut Function, isa: &TargetIsa) -> Result<CodeOffset
// This is an out-of-range branch.
// Relax it unless the destination offset has not been computed yet.
if dest_offset != 0 || Some(dest) == cur.func.layout.entry_block() {
offset += relax_branch(&mut cur, offset, dest_offset, &encinfo);
offset +=
relax_branch(&mut cur, offset, dest_offset, &encinfo, isa);
continue;
}
}
@@ -134,14 +135,36 @@ fn relax_branch(
offset: CodeOffset,
dest_offset: CodeOffset,
encinfo: &EncInfo,
isa: &TargetIsa,
) -> CodeOffset {
let inst = cur.current_inst().unwrap();
dbg!(
"Relaxing [{}] {} for {:#x}-{:#x} range",
encinfo.display(cur.func.encodings[inst]),
cur.func.dfg.display_inst(inst, None),
cur.func.dfg.display_inst(inst, isa),
offset,
dest_offset
);
// Pick the first encoding that can handle the branch range.
let dfg = &cur.func.dfg;
let ctrl_type = dfg.ctrl_typevar(inst);
if let Some(enc) = isa.legal_encodings(dfg, &dfg[inst], ctrl_type).find(
|&enc| {
let range = encinfo.branch_range(enc).expect("Branch with no range");
let in_range = range.contains(offset, dest_offset);
dbg!(
" trying [{}]: {}",
encinfo.display(enc),
if in_range { "OK" } else { "out of range" }
);
in_range
},
)
{
cur.func.encodings[inst] = enc;
return encinfo.bytes(enc);
}
unimplemented!();
}