Remove from cranelift too.

Author: cjgillot

compiler/rustc_codegen_cranelift/src/discriminant.rs

@@ -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.
@@ -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
@@ -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.
@@ -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.