isZeroInit

    pub fn isZeroInit(self: Constant, builder: *const Builder) bool {
        switch (self.unwrap()) {
            .constant => |constant| {
                const item = builder.constant_items.get(constant);
                return switch (item.tag) {
                    .positive_integer => {
                        const extra: *align(@alignOf(std.math.big.Limb)) Integer =
                            @ptrCast(builder.constant_limbs.items[item.data..][0..Integer.limbs]);
                        const limbs = builder.constant_limbs
                            .items[item.data + Integer.limbs ..][0..extra.limbs_len];
                        return std.mem.eql(std.math.big.Limb, limbs, &.{0});
                    },
                    .half, .bfloat, .float => item.data == 0,
                    .double => {
                        const extra = builder.constantExtraData(Constant.Double, item.data);
                        return extra.lo == 0 and extra.hi == 0;
                    },
                    .fp128, .ppc_fp128 => {
                        const extra = builder.constantExtraData(Constant.Fp128, item.data);
                        return extra.lo_lo == 0 and extra.lo_hi == 0 and
                            extra.hi_lo == 0 and extra.hi_hi == 0;
                    },
                    .x86_fp80 => {
                        const extra = builder.constantExtraData(Constant.Fp80, item.data);
                        return extra.lo_lo == 0 and extra.lo_hi == 0 and extra.hi == 0;
                    },
                    .vector => {
                        var extra = builder.constantExtraDataTrail(Aggregate, item.data);
                        const len: u32 = @intCast(extra.data.type.aggregateLen(builder));
                        const vals = extra.trail.next(len, Constant, builder);
                        for (vals) |val| if (!val.isZeroInit(builder)) return false;
                        return true;
                    },
                    .null, .zeroinitializer => true,
                    else => false,
                };
            },
            .global => return false,
        }
    }