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Remove from cranelift too.
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@cjgillot
cjgillot committed Apr 14, 2023
1 parent 446650c commit fe3e383
Showing 1 changed file with 0 additions and 89 deletions.
89 changes: 0 additions & 89 deletions src/discriminant.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -103,7 +103,6 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
}
};

let cast_to_size = dest_layout.layout.size();
let cast_to = fx.clif_type(dest_layout.ty).unwrap();

// Read the tag/niche-encoded discriminant from memory.
Expand All @@ -122,21 +121,7 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
dest.write_cvalue(fx, res);
}
TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start } => {
let tag_size = tag_scalar.size(fx);
let max_unsigned = tag_size.unsigned_int_max();
let max_signed = tag_size.signed_int_max() as u128;
let min_signed = max_signed + 1;
let relative_max = niche_variants.end().as_u32() - niche_variants.start().as_u32();
let niche_end = niche_start.wrapping_add(relative_max as u128) & max_unsigned;
let range = tag_scalar.valid_range(fx);

let sle = |lhs: u128, rhs: u128| -> bool {
// Signed and unsigned comparisons give the same results,
// except that in signed comparisons an integer with the
// sign bit set is less than one with the sign bit clear.
// Toggle the sign bit to do a signed comparison.
(lhs ^ min_signed) <= (rhs ^ min_signed)
};

// We have a subrange `niche_start..=niche_end` inside `range`.
// If the value of the tag is inside this subrange, it's a
Expand All @@ -153,45 +138,6 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
// }
// However, we will likely be able to emit simpler code.

// Find the least and greatest values in `range`, considered
// both as signed and unsigned.
let (low_unsigned, high_unsigned) =
if range.start <= range.end { (range.start, range.end) } else { (0, max_unsigned) };
let (low_signed, high_signed) = if sle(range.start, range.end) {
(range.start, range.end)
} else {
(min_signed, max_signed)
};

let niches_ule = niche_start <= niche_end;
let niches_sle = sle(niche_start, niche_end);
let cast_smaller = cast_to_size <= tag_size;

// In the algorithm above, we can change
// cast(relative_tag) + niche_variants.start()
// into
// cast(tag + (niche_variants.start() - niche_start))
// if either the casted type is no larger than the original
// type, or if the niche values are contiguous (in either the
// signed or unsigned sense).
let can_incr = cast_smaller || niches_ule || niches_sle;

let data_for_boundary_niche = || -> Option<(IntCC, u128)> {
if !can_incr {
None
} else if niche_start == low_unsigned {
Some((IntCC::UnsignedLessThanOrEqual, niche_end))
} else if niche_end == high_unsigned {
Some((IntCC::UnsignedGreaterThanOrEqual, niche_start))
} else if niche_start == low_signed {
Some((IntCC::SignedLessThanOrEqual, niche_end))
} else if niche_end == high_signed {
Some((IntCC::SignedGreaterThanOrEqual, niche_start))
} else {
None
}
};

let (is_niche, tagged_discr, delta) = if relative_max == 0 {
// Best case scenario: only one tagged variant. This will
// likely become just a comparison and a jump.
Expand All @@ -206,41 +152,6 @@ pub(crate) fn codegen_get_discriminant<'tcx>(
let tagged_discr =
fx.bcx.ins().iconst(cast_to, niche_variants.start().as_u32() as i64);
(is_niche, tagged_discr, 0)
} else if let Some((predicate, constant)) = data_for_boundary_niche() {
// The niche values are either the lowest or the highest in
// `range`. We can avoid the first subtraction in the
// algorithm.
// The algorithm is now this:
// is_niche = tag <= niche_end
// discr = if is_niche {
// cast(tag + (niche_variants.start() - niche_start))
// } else {
// untagged_variant
// }
// (the first line may instead be tag >= niche_start,
// and may be a signed or unsigned comparison)
// The arithmetic must be done before the cast, so we can
// have the correct wrapping behavior. See issue #104519 for
// the consequences of getting this wrong.
let is_niche = codegen_icmp_imm(fx, predicate, tag, constant as i128);
let delta = (niche_variants.start().as_u32() as u128).wrapping_sub(niche_start);
let incr_tag = if delta == 0 {
tag
} else {
let delta = match fx.bcx.func.dfg.value_type(tag) {
types::I128 => {
let lsb = fx.bcx.ins().iconst(types::I64, delta as u64 as i64);
let msb = fx.bcx.ins().iconst(types::I64, (delta >> 64) as u64 as i64);
fx.bcx.ins().iconcat(lsb, msb)
}
ty => fx.bcx.ins().iconst(ty, delta as i64),
};
fx.bcx.ins().iadd(tag, delta)
};

let cast_tag = clif_intcast(fx, incr_tag, cast_to, !niches_ule);

(is_niche, cast_tag, 0)
} else {
// The special cases don't apply, so we'll have to go with
// the general algorithm.
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