addInst

    fn addInst(
        self: *WipFunction,
        name: ?[]const u8,
        instruction: Instruction,
    ) Allocator.Error!Instruction.Index {
        const block_instructions = &self.cursor.block.ptr(self).instructions;
        try self.instructions.ensureUnusedCapacity(self.builder.gpa, 1);
        if (!self.strip) {
            try self.names.ensureUnusedCapacity(self.builder.gpa, 1);
            try self.debug_locations.ensureUnusedCapacity(self.builder.gpa, 1);
        }
        try block_instructions.ensureUnusedCapacity(self.builder.gpa, 1);
        const final_name = if (name) |n|
            if (self.strip) .empty else try self.builder.string(n)
        else
            .none;

        const index: Instruction.Index = @fromBackingInt(@intCast(self.instructions.len));
        self.instructions.appendAssumeCapacity(instruction);
        if (!self.strip) {
            self.names.appendAssumeCapacity(final_name);
            if (block_instructions.items.len == 0 or
                !std.meta.eql(self.debug_location, self.prev_debug_location))
            {
                self.debug_locations.putAssumeCapacity(index, self.debug_location);
                self.prev_debug_location = self.debug_location;
            }
        }
        block_instructions.insertAssumeCapacity(self.cursor.instruction, index);
        self.cursor.instruction += 1;
        return index;
    }