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Fix #686: Allow code shrink in relaxation if the shrinking pass hasn't been run;

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Also:
- make sure to apply diversions when determining offsets for code
relaxation.
- select the smallest encoding when selecting a relaxed branch
instruction.
This commit is contained in:
Benjamin Bouvier
2019-03-12 12:06:11 +01:00
parent 2dd1552369
commit cd8a42e01f
2 changed files with 58 additions and 6 deletions
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11
cranelift/codegen/src/binemit/relaxation.rs
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@@ -62,6 +62,7 @@ pub fn relax_branches(func: &mut Function, isa: &TargetIsa) -> CodegenResult<Cod
divert.clear();
cur.func.offsets[ebb] = offset;
while let Some(inst) = cur.next_inst() {
divert.apply(&cur.func.dfg[inst]);
let enc = cur.func.encodings[inst];
offset += encinfo.byte_size(enc, inst, &divert, &cur.func);
}
@@ -81,10 +82,6 @@ pub fn relax_branches(func: &mut Function, isa: &TargetIsa) -> CodegenResult<Cod
// Record the offset for `ebb` and make sure we iterate until offsets are stable.
if cur.func.offsets[ebb] != offset {
debug_assert!(
cur.func.offsets[ebb] < offset,
"Code shrinking during relaxation"
);
cur.func.offsets[ebb] = offset;
go_again = true;
}
@@ -173,12 +170,12 @@ fn relax_branch(
dest_offset
);
// Pick the first encoding that can handle the branch range.
// Pick the smallest 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(cur.func, &dfg[inst], ctrl_type)
.find(|&enc| {
.filter(|&enc| {
let range = encinfo.branch_range(enc).expect("Branch with no range");
if !range.contains(offset, dest_offset) {
debug!(" trying [{}]: out of range", encinfo.display(enc));
@@ -198,7 +195,9 @@ fn relax_branch(
true
}
})
.min_by_key(|&enc| encinfo.byte_size(enc, inst, &divert, &cur.func))
{
debug_assert!(enc != cur.func.encodings[inst]);
cur.func.encodings[inst] = enc;
return encinfo.byte_size(enc, inst, &divert, &cur.func);
}