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rustc_codegen_ssa: try to make codegen_get_discr more readable.

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This commit is contained in:
Eduard-Mihai Burtescu 2019-07-01 19:14:29 +03:00
parent 4bb6b4a5ed
commit e60c7ed0b0
1 changed files with 32 additions and 18 deletions
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50
src/librustc_codegen_ssa/mir/place.rs
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@ -228,8 +228,11 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
}
};
let discr = self.project_field(bx, discr_index);
let lldiscr = bx.load_operand(discr).immediate();
// Read the tag/niche-encoded discriminant from memory.
let encoded_discr = self.project_field(bx, discr_index);
let encoded_discr = bx.load_operand(encoded_discr);
// Decode the discriminant (specifically if it's niche-encoded).
match *discr_kind {
layout::DiscriminantKind::Tag => {
let signed = match discr_scalar.value {
@ -240,38 +243,49 @@ impl<'a, 'tcx, V: CodegenObject> PlaceRef<'tcx, V> {
layout::Int(_, signed) => !discr_scalar.is_bool() && signed,
_ => false
};
bx.intcast(lldiscr, cast_to, signed)
bx.intcast(encoded_discr.immediate(), cast_to, signed)
}
layout::DiscriminantKind::Niche {
dataful_variant,
ref niche_variants,
niche_start,
} => {
let niche_llty = bx.cx().immediate_backend_type(discr.layout);
if niche_variants.start() == niche_variants.end() {
let niche_llty = bx.cx().immediate_backend_type(encoded_discr.layout);
let encoded_discr = encoded_discr.immediate();
let (is_niche, niche_discr) = if niche_variants.start() == niche_variants.end() {
// Special case for when we can use a simple equality check,
// which covers null pointers, and needs simpler codegen.
// FIXME(eddyb): check the actual primitive type here.
let niche_llval = if niche_start == 0 {
let encoded_niche = if niche_start == 0 {
// HACK(eddyb): using `c_null` as it works on all types.
bx.cx().const_null(niche_llty)
} else {
bx.cx().const_uint_big(niche_llty, niche_start)
};
let select_arg = bx.icmp(IntPredicate::IntEQ, lldiscr, niche_llval);
bx.select(select_arg,
(
bx.icmp(IntPredicate::IntEQ, encoded_discr, encoded_niche),
bx.cx().const_uint(cast_to, niche_variants.start().as_u32() as u64),
bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
)
} else {
// Rebase from niche values to discriminant values.
// Rebase from niche values to discriminants, and check
// whether the result is in range for the niche variants.
// FIXME(#61696) the range check is sometimes incorrect.
let delta = niche_start.wrapping_sub(niche_variants.start().as_u32() as u128);
let lldiscr = bx.sub(lldiscr, bx.cx().const_uint_big(niche_llty, delta));
let lldiscr_max =
let niche_discr =
bx.sub(encoded_discr, bx.cx().const_uint_big(niche_llty, delta));
let niche_discr_max =
bx.cx().const_uint(niche_llty, niche_variants.end().as_u32() as u64);
let select_arg = bx.icmp(IntPredicate::IntULE, lldiscr, lldiscr_max);
let cast = bx.intcast(lldiscr, cast_to, false);
bx.select(select_arg,
cast,
bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64))
}
(
bx.icmp(IntPredicate::IntULE, niche_discr, niche_discr_max),
niche_discr,
)
};
let niche_discr = bx.intcast(niche_discr, cast_to, false);
bx.select(
is_niche,
niche_discr,
bx.cx().const_uint(cast_to, dataful_variant.as_u32() as u64),
)
}
}
}