/* Jitter: VM-independent mutable routine data structures.

   Copyright (C) 2016, 2017, 2018, 2019, 2020, 2022 Luca Saiu
   Updated in 2021 and 2025 by Luca Saiu
   Written by Luca Saiu

   This file is part of GNU Jitter.

   GNU Jitter is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   GNU Jitter is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with GNU Jitter.  If not, see <https://www.gnu.org/licenses/>. */


#include <stdio.h>
#include <stdbool.h>
#include <string.h>

#include <jitter/jitter.h>
#include <jitter/jitter-mmap.h>
#include <jitter/jitter-mutable-routine.h>
#include <jitter/jitter-vm.h>
#include <jitter/jitter-rewrite.h>
#include <jitter/jitter-specialize.h>

#include <jitter/jitter-hash.h>
#include <jitter/jitter-malloc.h>
#include <jitter/jitter-fatal.h>


/* Routine options.
 * ************************************************************************** */

/* Set the pointed mutable-routine-option struct to the default state. */
static void
jitter_initialize_options (struct jitter_mutable_routine_options *op)
{
  op->can_change = true;
  op->slow_registers_only = false;
  op->slow_literals_only = false;
  op->add_final_exitvm = true;
  op->optimization_rewriting = true;
}

/* Change the options in the given routine to make options unchangeable from now
   on.  This is harmless to call even if the options are already unchangeable.
   In practice this is called when appending labels and meta-instructions; it is
   not necessary to call when appending instruction parameters, as those always
   follow meta-instructions.  Based on the same reasoning, rewriting rules
   always follow instruction appending, so the low-level API only used for
   rewriting does not need to use this. */
static void
jitter_routine_make_options_unchangeable (struct jitter_mutable_routine *p)
{
  p->options.can_change = false;
}

/* Fail fatally if the options in the pointed routine are no changeable. */
static void
jitter_fail_unless_options_changeable (struct jitter_mutable_routine *p)
{
  if (! p->options.can_change)
    jitter_fatal ("cannot change options in non-empty routine");
}

void
jitter_set_mutable_routine_option_slow_registers_only
   (struct jitter_mutable_routine *p, bool option)
{
  jitter_fail_unless_options_changeable (p);
  p->options.slow_registers_only = option;
}

void
jitter_set_mutable_routine_option_slow_literals_only
   (struct jitter_mutable_routine *p, bool option)
{
  jitter_fail_unless_options_changeable (p);
  p->options.slow_literals_only = option;
}

void
jitter_set_mutable_routine_option_slow_literals_and_registers_only
   (struct jitter_mutable_routine *p, bool option)
{
  jitter_set_mutable_routine_option_slow_registers_only (p, option);
  jitter_set_mutable_routine_option_slow_literals_only (p, option);
}

void
jitter_set_mutable_routine_option_add_final_exitvm
   (struct jitter_mutable_routine *p, bool option)
{
  jitter_fail_unless_options_changeable (p);
  p->options.add_final_exitvm = option;
}

void
jitter_set_mutable_routine_option_optimization_rewriting
   (struct jitter_mutable_routine *p, bool option)
{
  jitter_fail_unless_options_changeable (p);
  p->options.optimization_rewriting = option;
}



/* Initialization and finalization
 * ************************************************************************** */

static void
jitter_initialize_routine (struct jitter_mutable_routine *p)
{
  p->stage = jitter_routine_stage_unspecialized;

  jitter_initialize_options (& p->options);
  p->expected_parameter_no = 0;
  p->rewritable_instruction_no = 0;
  p->current_instruction = NULL;
  p->next_uninitialized_parameter = NULL; /* An intentionally invalid value. */
  p->next_expected_parameter_type = NULL; /* An intentionally invalid value. */

  jitter_dynamic_buffer_initialize (& p->instructions);
  p->next_unused_opaque_label = 0;
  jitter_hash_initialize (& p->label_name_to_opaque_label);
  jitter_dynamic_buffer_initialize (& p->opaque_label_to_instruction_index);
  p->jump_targets = NULL;
  p->instruction_index_to_specialized_instruction_offset = NULL;

  jitter_dynamic_buffer_initialize (& p->specialized_routine);
  jitter_dynamic_buffer_initialize (& p->replicated_blocks);
  p->native_code = NULL;
  jitter_dynamic_buffer_initialize (& p->specialized_label_indices);

  /* No slow registers have been seen yet. */
  p->slow_register_per_class_no = 0;

  /* No executable routine exists yet for this routine. */
  p->executable_routine = NULL;
}

static void
jitter_finalize_routine (struct jitter_mutable_routine *p)
{
  struct jitter_dynamic_buffer * const is = & p->instructions;
  while (jitter_dynamic_buffer_size (is) != 0)
    {
      struct jitter_instruction *i
        = * (struct jitter_instruction **)
            jitter_dynamic_buffer_pop (is, sizeof (struct jitter_instruction*));
      jitter_destroy_instruction (i);
    }
  jitter_dynamic_buffer_finalize (is);

  jitter_string_hash_finalize (& p->label_name_to_opaque_label, NULL);
  jitter_dynamic_buffer_finalize (& p->opaque_label_to_instruction_index);

  if (p->jump_targets != NULL)
    free (p->jump_targets);
  if (p->instruction_index_to_specialized_instruction_offset != NULL)
    free (p->instruction_index_to_specialized_instruction_offset);

  /* The specialized_routine field may have been extracted, if this routine has
     been made executable; in any case, this finalization will be valid. */
  jitter_dynamic_buffer_finalize (& p->specialized_routine);

  jitter_dynamic_buffer_finalize (& p->replicated_blocks);

#ifdef JITTER_REPLICATE
  /* The native_code field may be NULL because native code has never been
     generated, but also if the routine was made executable.  In either case the
     pointer field here will be NULL, so that we don't deallocate twice.  */
  if (p->native_code != NULL)
    jitter_executable_deallocate (p->native_code);
#endif // #ifdef JITTER_REPLICATE
  jitter_dynamic_buffer_finalize (& p->specialized_label_indices);
}

struct jitter_mutable_routine*
jitter_make_mutable_routine (const struct jitter_vm *vm)
{
  struct jitter_mutable_routine *res = jitter_xmalloc (sizeof (struct jitter_mutable_routine));
  jitter_initialize_routine (res);
  res->vm = vm;
  return res;
}

void
jitter_destroy_mutable_routine (struct jitter_mutable_routine *p)
{
  /* Unlink the executable routine, if any. */
  if (p->executable_routine != NULL)
    p->executable_routine->routine = NULL;

  if (p == NULL)
    return;

  jitter_finalize_routine (p);
  free (p);
}

size_t
jitter_mutable_routine_instruction_no (const struct jitter_mutable_routine *p)
{
  return jitter_dynamic_buffer_size (& p->instructions)
         / sizeof (struct jitter_instruction*);
}




/* Label handing.
 * ************************************************************************** */

jitter_label
jitter_fresh_label (struct jitter_mutable_routine *p)
{
  /* Allocate an identifier. */
  jitter_label res = p->next_unused_opaque_label ++;

  /* Associate the label to an invalid instruction index. */
  jitter_int invalid_instruction_index = -1;
  jitter_dynamic_buffer_push (& p->opaque_label_to_instruction_index,
                              & invalid_instruction_index,
                              sizeof (invalid_instruction_index));

  /* Return the identifier. */
  return res;
}

jitter_label
jitter_symbolic_label (struct jitter_mutable_routine *p, const char *symbolic_name)
{
  /* If the name is already known, return its label. */
  if (jitter_string_hash_table_has (& p->label_name_to_opaque_label,
                                    symbolic_name))
    return jitter_string_hash_table_get (& p->label_name_to_opaque_label,
                                         symbolic_name).fixnum;

  /* The name is new.  Allocate a new label, bind it to a copy of the name
     (copies are handled by the hash table routines), and return the label. */
  jitter_label res = jitter_fresh_label (p);
  union jitter_word datum = {.fixnum = res};
  jitter_string_hash_table_add (& p->label_name_to_opaque_label,
                                symbolic_name,
                                datum);
  return res;
}

/* Return the unspecialized instruction index for the given label in the pointed
   routine, or -1 if the label is not associated to any instruction.
   Unspecified behavior if the label is out of bounds. */
static jitter_int
jitter_get_label_instruction_index (struct jitter_mutable_routine *p,
                                    jitter_label label)
{
  jitter_int *array
    = jitter_dynamic_buffer_to_pointer (& p->opaque_label_to_instruction_index);

  return array [label];
}

/* Associate the given label in the pointed routine to the given unspecialized
   instruction index.  Fail fatally if the label was already associated to an
   index.  Unspecified behavior if the label is out of bounds. */
static void
jitter_set_label_instruction_index (struct jitter_mutable_routine *p,
                                    jitter_label label,
                                    jitter_int instruction_index)
{
  jitter_int *array
    = jitter_dynamic_buffer_to_pointer (& p->opaque_label_to_instruction_index);
  jitter_int previous_index = array [label];
  if (previous_index != -1)
    jitter_fatal ("label %li appended twice", (long) label);

  array [label] = instruction_index;
}




/* Mutable routine construction API: functions which cannot fail.
 * ************************************************************************** */




/* Mutable routine construction API: safe functions.
 * ************************************************************************** */

/* Forward-declarations. */
static void
jitter_close_current_instruction (struct jitter_mutable_routine *p);
static struct jitter_parameter *
jitter_mutable_routine_append_uninitialized_parameter
   (struct jitter_mutable_routine *p,
    enum jitter_parameter_type actual_type,
    const struct jitter_register_class *register_class);
static void
jitter_close_instruction_when_no_more_parameters (struct jitter_mutable_routine *p);

  enum jitter_routine_edit_status
jitter_mutable_routine_append_label_safe (struct jitter_mutable_routine *p,
                                          jitter_label label)
{
  if (p->stage != jitter_routine_stage_unspecialized)
    jitter_fatal ("appending label in non non-unspecialized routine");
  if (p->expected_parameter_no != 0)
    return jitter_routine_edit_status_last_instruction_incomplete;
  if (jitter_get_label_instruction_index (p, label) != -1)
    return jitter_routine_edit_status_label_defined_twice;
  jitter_routine_make_options_unchangeable (p);

  jitter_int instruction_index = jitter_mutable_routine_instruction_no (p);
  jitter_set_label_instruction_index (p, label, instruction_index);

  /* We added a label.  Everything before it can no longer be rewritten. */
  p->rewritable_instruction_no = 0;
  return jitter_routine_edit_status_success;
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_symbolic_label_safe
   (jitter_label *result, /* This is allowed to be NULL. */
    struct jitter_mutable_routine *p,
    const char *label_name)
{
  jitter_label label = jitter_symbolic_label (p, label_name);
  if (result != NULL)
    * result = label;
  return jitter_mutable_routine_append_label_safe (p, label);
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_instruction_name_safe
   (struct jitter_mutable_routine *p,
    const char *instruction_name)
{
  const struct jitter_meta_instruction * const mi
    = jitter_lookup_meta_instruction (p->vm->meta_instruction_string_hash,
                                      instruction_name);
  if (mi == NULL)
    return jitter_routine_edit_status_invalid_instruction;
  else
    return jitter_mutable_routine_append_meta_instruction_safe (p, mi);
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_instruction_id_safe
   (struct jitter_mutable_routine *p,
    const struct jitter_meta_instruction * const mis,
    size_t meta_instruction_no,
    unsigned unspecialized_opcode)
{
  /* Sanity check. */
  if (unspecialized_opcode >= meta_instruction_no)
    return jitter_routine_edit_status_invalid_instruction;

  /* Find the address of the appropriate meta-instruction in the array. */
  const struct jitter_meta_instruction * const mi
    = mis + unspecialized_opcode;

  /* Append the meta-instruction. */
  return jitter_mutable_routine_append_meta_instruction_safe (p, mi);
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_meta_instruction_safe
   (struct jitter_mutable_routine *p,
    const struct jitter_meta_instruction * const mi)
{
  if (p->stage != jitter_routine_stage_unspecialized)
    jitter_fatal ("appending instruction %s in non-unspecialized routine",
                  mi->name);
  if (p->expected_parameter_no != 0)
    return jitter_routine_edit_status_last_instruction_incomplete;
  jitter_routine_make_options_unchangeable (p);

  /* Make the instruction. */
  struct jitter_instruction *i
    = p->current_instruction
    = jitter_make_instruction (mi);

  /* Add a pointer to it to the dynamic buffer for instructions within the
     routine. */
  jitter_dynamic_buffer_push (& p->instructions,
                              & i,
                              sizeof (struct jitter_meta_instruction *));

  /* If this instruction has zero parameters then we're already done with it,
     and we can close it immediately.  Otherwise set parameter pointers to the
     first parameter to be appended. */
  if ((p->expected_parameter_no = mi->parameter_no) == 0)
    jitter_close_current_instruction (p);
  else
    {
      p->next_uninitialized_parameter = i->parameters [0];
      p->next_expected_parameter_type = mi->parameter_types;
    }

  return jitter_routine_edit_status_success;
}

/* Return the status that we would get after adding a parameter of the given
   kind (and, if register, register class) to the pointed mutable routine, but
   do not modify the routine.  Fail fatally if the routine is not
   unspecialised. */
static enum jitter_routine_edit_status
jitter_mutable_routine_check_next_parameter_safe
   (struct jitter_mutable_routine *p,
    enum jitter_parameter_type actual_type,
    const struct jitter_register_class *register_class)
{
  if (p->stage != jitter_routine_stage_unspecialized)
    jitter_fatal ("appending parameter in non-unspecialized routine");
  if (p->expected_parameter_no == 0)
    return jitter_routine_edit_status_too_many_parameters;
  if (p->next_expected_parameter_type == NULL)
    jitter_fatal ("impossible if we passed the previous check");

  /* Check that the parameter type is compatible with what we expect. */
  const struct jitter_meta_instruction_parameter_type * expected_type =
    p->next_expected_parameter_type;
  enum jitter_meta_instruction_parameter_kind expected_kind
    = expected_type->kind;
  /* FIXME: this logic is quite ugly: in jitterc, which I wrote later, expected
     parameter kinds are a bitmask.  That is much more flexible.  I should unify
     those types. */
  switch (actual_type)
    {
    case jitter_parameter_type_register_id:
      if (   expected_kind
             != jitter_meta_instruction_parameter_kind_register
          && expected_kind
             != jitter_meta_instruction_parameter_kind_register_or_literal_fixnum
          && expected_kind
             != jitter_meta_instruction_parameter_kind_register_or_literal_label
          && expected_kind
             != jitter_meta_instruction_parameter_kind_register_or_literal_fixnum_or_literal_label)
        return jitter_routine_edit_status_invalid_parameter_kind;
      if (expected_type->register_class != register_class)
        return jitter_routine_edit_status_register_class_mismatch;
      else
        return jitter_routine_edit_status_success;
    case jitter_parameter_type_literal:
      if (   expected_kind
             != jitter_meta_instruction_parameter_kind_literal_fixnum
          && expected_kind
             != jitter_meta_instruction_parameter_kind_literal_fixnum_or_literal_label
          && expected_kind
             != jitter_meta_instruction_parameter_kind_register_or_literal_fixnum
          && expected_kind
             != jitter_meta_instruction_parameter_kind_register_or_literal_fixnum_or_literal_label)
        return jitter_routine_edit_status_invalid_parameter_kind;
      else
        return jitter_routine_edit_status_success;
    case jitter_parameter_type_label:
      if (   expected_kind
             != jitter_meta_instruction_parameter_kind_literal_label
          && expected_kind
             != jitter_meta_instruction_parameter_kind_literal_fixnum_or_literal_label
          && expected_kind
             != jitter_meta_instruction_parameter_kind_register_or_literal_label
          && expected_kind
             != jitter_meta_instruction_parameter_kind_register_or_literal_fixnum_or_literal_label)
        return jitter_routine_edit_status_invalid_parameter_kind;
      else
        return jitter_routine_edit_status_success;
    default:
      jitter_fatal ("jitter_mutable_routine_check_next_parameter_safe: "
                    "invalid actual argument type %lu",
                    (unsigned long) actual_type);
    }
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_literal_parameter_safe
   (struct jitter_mutable_routine *p,
    union jitter_word immediate)
{
  /* Check if the parameter is compatible; if not return failure. */
  enum jitter_routine_edit_status res
    = jitter_mutable_routine_check_next_parameter_safe
         (p, jitter_parameter_type_literal, NULL);
  if (res != jitter_routine_edit_status_success)
    return res;

  /* Now it is safe to use unsafe functions: no failure is possible. */
  struct jitter_parameter * const pa
    = jitter_mutable_routine_append_uninitialized_parameter
         (p, jitter_parameter_type_literal, NULL);
  pa->type = jitter_parameter_type_literal;
  pa->literal = immediate;
  jitter_close_instruction_when_no_more_parameters (p);

  return jitter_routine_edit_status_success;
}

/* These are just convenience wrappers. */
enum jitter_routine_edit_status
jitter_mutable_routine_append_signed_literal_parameter_safe
   (struct jitter_mutable_routine *p,
    jitter_int immediate)
{
  union jitter_word u = {.fixnum = immediate};
  return jitter_mutable_routine_append_literal_parameter_safe (p, u);
}
enum jitter_routine_edit_status
jitter_mutable_routine_append_unsigned_literal_parameter_safe
   (struct jitter_mutable_routine *p,
    jitter_uint immediate)
{
  union jitter_word u = {.ufixnum = immediate};
  return jitter_mutable_routine_append_literal_parameter_safe (p, u);
}
enum jitter_routine_edit_status
jitter_mutable_routine_append_pointer_literal_parameter_safe
   (struct jitter_mutable_routine *p,
    void *immediate)
{
  union jitter_word u = {.pointer = immediate};
  return jitter_mutable_routine_append_literal_parameter_safe (p, u);
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_register_parameter_safe
   (struct jitter_mutable_routine *p,
    const struct jitter_register_class *c,
    jitter_register_index register_index)
{
  /* Check if the parameter is compatible; if not return failure. */
  enum jitter_routine_edit_status res
    = jitter_mutable_routine_check_next_parameter_safe
         (p, jitter_parameter_type_register_id, c);
  if (res != jitter_routine_edit_status_success)
    return res;

  /* Now it is safe to use unsafe functions: no failure is possible. */

  /* If we have to always residualize registers, then increment this register
     index by the number of fast registers in the class.  This way it is
     guaranteed that the actual register used in execution will be slow.  (When
     printing out the routine the register index will be shown *decremented* by
     the number of fast registers in the class to compensate for this.) */
  if (p->options.slow_registers_only)
    register_index += c->fast_register_no;

  /* Append the register parameter. */
  struct jitter_parameter * const pa
    = jitter_mutable_routine_append_uninitialized_parameter
         (p, jitter_parameter_type_register_id, c);
  pa->type = jitter_parameter_type_register_id;
  pa->register_index = register_index;
  pa->register_class = c;

  /* If this register is slow and its slow index is the highest up to this
     point, record it: it will be needed to know how many slow registers to
     allocate.  Notice that a negative slow_index (indicating a fast register)
     will never satisfy the if condition, as p->slow_register_per_class_no is
     initialized to zero and non-decreasing. */
  jitter_int slow_index = register_index - c->fast_register_no;
  jitter_int slow_register_no = slow_index + 1;
  if (slow_register_no > p->slow_register_per_class_no)
    p->slow_register_per_class_no = slow_register_no;
  jitter_close_instruction_when_no_more_parameters (p);

  return jitter_routine_edit_status_success;
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_symbolic_register_parameter_safe
   (struct jitter_mutable_routine *p,
    char register_class_as_char,
    jitter_register_index register_index)
{
  const struct jitter_register_class *register_class
    = p->vm->register_class_character_to_register_class (register_class_as_char);
  if (register_class == NULL)
    return jitter_routine_edit_status_nonexisting_register_class;
  return jitter_mutable_routine_append_register_parameter_safe (p,
                                                                register_class,
                                                                register_index);
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_label_parameter_safe
   (struct jitter_mutable_routine *p,
    jitter_label label)
{
  /* Check if the parameter is compatible; if not return failure. */
  enum jitter_routine_edit_status res
    = jitter_mutable_routine_check_next_parameter_safe
         (p, jitter_parameter_type_label, NULL);
  if (res != jitter_routine_edit_status_success)
    return res;

  /* Do the actual work. */
  struct jitter_parameter * const pa
    = jitter_mutable_routine_append_uninitialized_parameter
         (p, jitter_parameter_type_label, NULL);
  pa->type = jitter_parameter_type_label;
  pa->label = label;
  jitter_close_instruction_when_no_more_parameters (p);
  return jitter_routine_edit_status_success;
}

enum jitter_routine_edit_status
jitter_mutable_routine_append_symbolic_label_parameter_safe
   (jitter_label *label_pointer,
    struct jitter_mutable_routine *p,
    const char *label_name)
{
  /* It would be tempting to just call jitter_symbolic_label, and then defer
     the work to jitter_mutable_routine_append_label_parameter_safe .  That does
     not work unfortunately, because in case of errors we would stull add a
     new label: it is necessary to first check that there is no error... */
  enum jitter_routine_edit_status res
    = jitter_mutable_routine_check_next_parameter_safe
         (p, jitter_parameter_type_label, NULL);
  if (res != jitter_routine_edit_status_success)
    return res;

  /* ...And now we can in fact use the non-symbolic variant. */
  jitter_label label = jitter_symbolic_label (p, label_name);
  if (label_pointer != NULL)
    * label_pointer = label;
  return jitter_mutable_routine_append_label_parameter_safe (p, label);
}




/* Mutable routine construction API: unsafe functions.
 * ************************************************************************** */

void
jitter_mutable_routine_append_label (struct jitter_mutable_routine *p, jitter_label label)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_label_safe (p, label);
  switch (s)
    {
    case jitter_routine_edit_status_label_defined_twice:
      jitter_fatal ("appending label %li which had been defined already",
                    (long) label);
    case jitter_routine_edit_status_last_instruction_incomplete:
      jitter_fatal ("appending label %li with previous instruction "
                    "incomplete", (long) label);
    case jitter_routine_edit_status_success:  break;
    default:  jitter_fatal ("this should not happen MA1");
    }
}

jitter_label
jitter_mutable_routine_append_symbolic_label (struct jitter_mutable_routine *p, const char *label_name)
{
  jitter_label label;
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_symbolic_label_safe (& label, p, label_name);
  switch (s)
    {
    case jitter_routine_edit_status_label_defined_twice:
      jitter_fatal ("appending label %s which had been defined already",
                    label_name);
    case jitter_routine_edit_status_last_instruction_incomplete:
      jitter_fatal ("appending label %s with previous instruction "
                    "incomplete", label_name);
    case jitter_routine_edit_status_success:
      return label;
    default:  jitter_fatal ("this should not happen MA1");
    }
}

/* Close the current instruction which must have all of its parameters already
   added (fail fatally otherwise), by calling the rewriter on it.  Set pointers
   about the next parameter in the routine to reflect the fact that its address
   is not known yet, and a new instruction is expected first.  Increment the
   instruction counter. */
static void
jitter_close_current_instruction (struct jitter_mutable_routine *p)
{
  if (p->stage != jitter_routine_stage_unspecialized)
    jitter_fatal ("closing instruction in non-unspecialized routine");
  if (p->expected_parameter_no != 0)
    jitter_fatal ("closing an instruction still expecting parameters");

  p->next_uninitialized_parameter = NULL;
  p->next_expected_parameter_type = NULL;

  /* The instruction we just added is a candidate for rewriting, along with the
     previous ones which were candidate already. */
  p->rewritable_instruction_no ++;

  /* Unless optimization rewrites were disabled for this routine, rewrite the
     last part of the routine, using the instruction we have just closed; that
     instruction, along with some others preceding it, might very well change or
     disappear after rewriting is done. */
  if (p->options.optimization_rewriting)
    p->vm->rewrite (p);
}

/* Check that the pointed routine's last instruction is incomplete, and that the
   next parameter it expects is compatible with the given actual type and, in
   case it's a register, register class.  Fail fatally if that's not the
   case. */
static void
jitter_check_parameter_compatibility
   (struct jitter_mutable_routine *p,
    enum jitter_parameter_type actual_type,
    const struct jitter_register_class *register_class)
{
  /* Check that the routine is in the right stage, and that we're
     actually expecting a parameter. */
  if (p->stage != jitter_routine_stage_unspecialized)
    jitter_fatal ("appending parameter in non-unspecialized routine");

  /* Throw a fatal error on any failure. */
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_check_next_parameter_safe (p, actual_type,
                                                        register_class);
  switch (s)
    {
    case jitter_routine_edit_status_success:
      /* No errors: nothing to do. */
      return;
    case jitter_routine_edit_status_invalid_register:
      jitter_fatal ("invalid register parameter");
    case jitter_routine_edit_status_register_class_mismatch:
      jitter_fatal ("register class mismatch adding parameter");
    case jitter_routine_edit_status_nonexisting_register_class:
      jitter_fatal ("nonexisting register class adding parameter");
    case jitter_routine_edit_status_invalid_parameter_kind:
      jitter_fatal ("invalid parameter kind");
    case jitter_routine_edit_status_too_many_parameters:
      jitter_fatal ("too many parameters");
    default:
      jitter_fatal ("this should not happen MA10");
    }
}

/* Make the current instruction, which must be incomplete, have the next
   expected parameter as its own and start a new instruction if that parameter
   was the last, but *don't* close the old instruction.  Don't do checks. */
static void
jitter_advance_past_next_parameter (struct jitter_mutable_routine *p)
{
  if ((-- p->expected_parameter_no) != 0)
    {
      const struct jitter_instruction *in = p->current_instruction;
      const struct jitter_meta_instruction *min = in->meta_instruction;

      /* There are other parameters expected in the current instruction after
         the one we have just added.  Point to the next one. */
      p->next_uninitialized_parameter
        = in->parameters [min->parameter_no - p->expected_parameter_no];
      p->next_expected_parameter_type ++;
    }
}

/* Add a parameter of the given parameter type (which is a
   jitter_parameter_type, therefore an "actual" type and *not* a
   jitter_meta_instruction_parameter type, expressing the set of "formal"
   accepted types) to the last instruction of the given unspecialized routine,
   which must be incomplete.  A register class is also given to check that it
   matches with the expected parameter, in case of a register-type parameter; it
   is ignored otherwise.
   Fail fatally if the routine is not unspecialized
   or its last instruction is complete, or if the kind or register class is
   wrong.  Return a pointer to the parameter data structure, to be filled in by
   the caller.  In any case, do *not* close the instruction, even if the appended
   parameter was the last; doing that would interfere badly with rewriting, which
   has to see every parameter correctly initialized.
   This is used by jitter_mutable_routine_append_literal_parameter_safe ,
   jitter_mutable_routine_append_register_parameter_safe and
   jitter_mutable_routine_append_label_parameter_safe -- after
   checking that what we are doing here is indeed correct. */
static struct jitter_parameter *
jitter_mutable_routine_append_uninitialized_parameter
   (struct jitter_mutable_routine *p,
    enum jitter_parameter_type actual_type,
    const struct jitter_register_class *register_class)
{
  /* Check that the parameter is compatbile; fail fatally if it isn't. */
  jitter_check_parameter_compatibility (p, actual_type, register_class);

  /* Keep a pointer to the next uninitialized parameter to be returned; it will
     no longer be the next at the end of this function. */
  struct jitter_parameter *res = p->next_uninitialized_parameter;

  /* Advance pointers in the routine past this parameter, starting a new
     instruction if needed -- but don't close the current instruction: see the
     comment before this function. */
  jitter_advance_past_next_parameter (p);

  return res;
}

/* Close the current instruction if the last appended parameter was the last
   one.  See the comment before as to why this is not done there. */
static void
jitter_close_instruction_when_no_more_parameters (struct jitter_mutable_routine
                                                  *p)
{
  if (p->expected_parameter_no == 0)
    jitter_close_current_instruction (p);
}

void
jitter_mutable_routine_append_literal_parameter
   (struct jitter_mutable_routine *p,
    union jitter_word immediate)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_literal_parameter_safe (p, immediate);
  switch (s)
    {
    case jitter_routine_edit_status_too_many_parameters:
      jitter_fatal ("excess (literal) parameter");
    case jitter_routine_edit_status_invalid_parameter_kind:
      jitter_fatal ("invalid parameter kind (literal)");
    case jitter_routine_edit_status_success:
      return;
    default:  jitter_fatal ("this should not happen MA6");
    }
}

/* These are just convenience wrappers around
   jitter_mutable_routine_append_literal_parameter . */
void
jitter_mutable_routine_append_signed_literal_parameter
   (struct jitter_mutable_routine *p,
    jitter_int immediate)
{
  union jitter_word immediate_union = {.fixnum = immediate};
  jitter_mutable_routine_append_literal_parameter (p, immediate_union);
}
void
jitter_mutable_routine_append_unsigned_literal_parameter
   (struct jitter_mutable_routine *p,
    jitter_uint immediate)
{
  union jitter_word immediate_union = {.ufixnum = immediate};
  jitter_mutable_routine_append_literal_parameter (p, immediate_union);
}
void
jitter_mutable_routine_append_pointer_literal_parameter
   (struct jitter_mutable_routine *p,
    void *immediate)
{
  union jitter_word immediate_union = {.pointer = immediate};
  jitter_mutable_routine_append_literal_parameter (p, immediate_union);
}

void
jitter_mutable_routine_append_register_parameter
   (struct jitter_mutable_routine *p,
    const struct jitter_register_class *register_class,
    jitter_register_index register_index)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_register_parameter_safe (p, register_class,
                                                             register_index);
  switch (s)
    {
    case jitter_routine_edit_status_too_many_parameters:
      jitter_fatal ("excess (register) parameter");
    case jitter_routine_edit_status_invalid_parameter_kind:
      jitter_fatal ("invalid parameter kind (register)");
    case jitter_routine_edit_status_invalid_register:
      jitter_fatal ("invalid register parameter %%%c%i",
                    register_class->character, (int) register_index);
    case jitter_routine_edit_status_register_class_mismatch:
      jitter_fatal ("mismatching register class \'%c\' in parameter",
                    register_class->character);
    case jitter_routine_edit_status_success:
      return;
    default:  jitter_fatal ("this should not happen MA7");
    }
}

void
jitter_mutable_routine_append_symbolic_register_parameter
   (struct jitter_mutable_routine *p,
    char register_class_as_char,
    jitter_register_index register_index)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_symbolic_register_parameter_safe
         (p, register_class_as_char, register_index);
  switch (s)
    {
    case jitter_routine_edit_status_too_many_parameters:
      jitter_fatal ("excess (register) parameter");
    case jitter_routine_edit_status_invalid_parameter_kind:
      jitter_fatal ("invalid parameter kind (register)");
    case jitter_routine_edit_status_invalid_register:
      jitter_fatal ("invalid register parameter %%%c%i",
                    register_class_as_char, (int) register_index);
    case jitter_routine_edit_status_register_class_mismatch:
      jitter_fatal ("mismatching register class \'%c\' in parameter",
                    register_class_as_char);
    case jitter_routine_edit_status_nonexisting_register_class:
      jitter_fatal ("nonexisting register class \'%c\' in parameter",
                    register_class_as_char);
    case jitter_routine_edit_status_success:
      return;
    default:  jitter_fatal ("this should not happen MA8");
    }
}

jitter_label
jitter_mutable_routine_append_symbolic_label_parameter
   (struct jitter_mutable_routine *p, const char *label_name)
{
  jitter_label label;
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_symbolic_label_parameter_safe (& label,
                                                                   p,
                                                                   label_name);
  switch (s)
    {
    case jitter_routine_edit_status_too_many_parameters:
      jitter_fatal ("excess (register) parameter");
    case jitter_routine_edit_status_invalid_parameter_kind:
      jitter_fatal ("invalid parameter kind (register)");
    case jitter_routine_edit_status_success:
      return label;
    default:  jitter_fatal ("this should not happen MA9");
    }
}
void
jitter_mutable_routine_append_label_parameter (struct jitter_mutable_routine *p,
                                               jitter_label label)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_label_parameter_safe (p, label);
  switch (s)
    {
    case jitter_routine_edit_status_too_many_parameters:
      jitter_fatal ("excess (label) parameter");
    case jitter_routine_edit_status_invalid_parameter_kind:
      jitter_fatal ("invalid parameter kind (label)");
    case jitter_routine_edit_status_success:
      return;
    default:  jitter_fatal ("this should not happen MA9");
    }
}

void
jitter_mutable_routine_append_meta_instruction
   (struct jitter_mutable_routine *p,
    const struct jitter_meta_instruction * const mi)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_meta_instruction_safe (p, mi);
  switch (s)
    {
    case jitter_routine_edit_status_invalid_instruction:
      jitter_fatal ("appending invalid instruction %s", mi->name);
    case jitter_routine_edit_status_last_instruction_incomplete:
      jitter_fatal ("appending instruction %s with previous instruction "
                    "incomplete", mi->name);
    case jitter_routine_edit_status_success:
      break;
    default:
      jitter_fatal ("this should not happen MA5");
    }
}

void
jitter_mutable_routine_append_instruction_id (struct jitter_mutable_routine *p,
                              const struct jitter_meta_instruction * const mis,
                              size_t meta_instruction_no,
                              unsigned unspecialized_opcode)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_instruction_id_safe (p, mis,
                                                         meta_instruction_no,
                                                         unspecialized_opcode);
  switch (s)
    {
    case jitter_routine_edit_status_invalid_instruction:
      jitter_fatal ("appending instruction with invalid id %u",
                    unspecialized_opcode);
    case jitter_routine_edit_status_last_instruction_incomplete:
      jitter_fatal ("appending instruction with previous instruction "
                    "incomplete");
    case jitter_routine_edit_status_success:
      return;
    default:  jitter_fatal ("this should not happen MA4");
    }
}

void
jitter_mutable_routine_append_instruction_name (struct jitter_mutable_routine *p,
                                                const char *instruction_name)
{
  enum jitter_routine_edit_status s
    = jitter_mutable_routine_append_instruction_name_safe (p, instruction_name);
  switch (s)
    {
    case jitter_routine_edit_status_invalid_instruction:
      jitter_fatal ("appending invalid instruction %s", instruction_name);
    case jitter_routine_edit_status_last_instruction_incomplete:
      jitter_fatal ("appending instruction %s with previous instruction "
                    "incomplete", instruction_name);
    case jitter_routine_edit_status_success:
      break;
    default:  jitter_fatal ("this should not happen MA2");
    }
}




/* Lower-level routine-construction API.
 * ************************************************************************** */

void
jitter_mutable_routine_append_instruction (struct jitter_mutable_routine *p,
                           const struct jitter_instruction *ip)
{
  if (p->stage != jitter_routine_stage_unspecialized)
    jitter_fatal ("jitter_mutable_routine_append_instruction: non non-unspecialized routine");
  if (p->expected_parameter_no != 0)
    jitter_fatal ("jitter_mutable_routine_append_instruction: previous instruction incomplete");
  fprintf (stderr, "Pushing instruction at %p (%s)\n", ip,
           ip->meta_instruction->name);

  /* Add the provided instruction.  There is no need to touch the fields about
     expected parameters, since the previous instruction was already closed. */
  jitter_dynamic_buffer_push (& p->instructions,
                              & ip,
                              sizeof (struct jitter_instruction*));

  /* Close the new instruction.  This increments the number of rewritable
     instructions and triggers rewriting.  Notice that the instruction that was
     just added, along with some others preceding it, might very well change or
     disappear after rewriting is done. */
  jitter_close_current_instruction (p);
}

void
jitter_mutable_routine_append_parameter_copy (struct jitter_mutable_routine *p,
                                              const struct jitter_parameter *pp)
{
  /* Check that the parameter is compatbile with what we are expecting; fail
     fatally if it isn't. */
  jitter_check_parameter_compatibility (p, pp->type, pp->register_class);

  /* The next parameter is pre-allocated.  Copy the pointed one into it. */
  jitter_copy_instruction_parameter (p->next_uninitialized_parameter, pp);

  /* Advance pointers in the routine past this parameter, starting a new
     instruction if needed.  This however doesn't close the instruction... */
  jitter_advance_past_next_parameter (p);

  /* ...So do it if needed. */
  jitter_close_instruction_when_no_more_parameters (p);
}




/* Jump target computation on unspecialized routines.
 * ************************************************************************** */

bool*
jitter_mutable_routine_jump_targets (const struct jitter_mutable_routine *p)
{
  if (p->expected_parameter_no != 0)
    jitter_fatal ("computing jump targets with an instruction incomplete");

  const int instruction_no = jitter_mutable_routine_instruction_no (p);
  const struct jitter_instruction **ins
    = (const struct jitter_instruction **)
      jitter_dynamic_buffer_to_const_pointer (& p->instructions);
  bool *res = jitter_xmalloc (sizeof (bool) * instruction_no);

  /* Initialize: no instruction is a jump target by default. */
  int i;
  for (i = 0; i < instruction_no; i ++)
    res [i] = false;

  /* Scan every instruction... */
  for (i = 0; i < instruction_no; i ++)
    {
      const struct jitter_parameter **ps
        = (const struct jitter_parameter **) ins[i]->parameters;

      /* Any callee instruction is a branch target, reachable by a
         branch-and-link. */
      if (ins [i]->meta_instruction->callee)
        res [i] = true;

      /* Any instruction directly *following* a caller instruction is a branch
         target, implicitly reachable by a return. */
      if (ins [i]->meta_instruction->caller && (i + 1) < instruction_no)
        res [i + 1] = true;

      /* Look at every argument of the i-th instruction: for every one referring
         another instruction as a jump target, set the target to true. */
      const int arity = ins[i]->meta_instruction->parameter_no;
      int j;
      for (j = 0; j < arity; j ++)
        {
          const struct jitter_parameter *p = ps [j];
          if (p->type == jitter_parameter_type_label)
            {
              const long target = p->label_as_index;
              if (target < 0 || target >= instruction_no)
                {
                  printf ("# Warning: invalid label literal in instruction "
                          "at L%li\n", (long) i);
                  res [i] = true; /* Make the invalid instruction visible. */
                }
              else
                res [target] = true;
            }
        } /* inner for: parameter loop. */
    } /* outer for: instruction loop. */

  return res;
}




/* Unspecialized routine printer.
 * ************************************************************************** */

/* Return the length of the longest instruction name actually used in this
   routine. */
static size_t
jitter_maximum_instruction_name_length (const struct jitter_mutable_routine *p)
{
  const int instruction_no = jitter_mutable_routine_instruction_no (p);
  const struct jitter_instruction **ins
    = (const struct jitter_instruction **)
      jitter_dynamic_buffer_to_const_pointer (& p->instructions);

  /* Iterate on every instruction, and find the maximum length. */
  size_t res = 0;
  int i;
  for (i = 0; i < instruction_no; i ++)
    {
      const struct jitter_instruction * in = ins [i];
      const struct jitter_meta_instruction * mi = in->meta_instruction;
      size_t instruction_name_length = strlen (mi->name);
      if (instruction_name_length > res)
        res = instruction_name_length;
    }
  return res;
}

/* Begin using a class in the given print context, where the class name is
   formed by the concatenation of the lower-case prefix for the VM of the
   pointed mutable routine, concatenated to a dash, concatenated to the
   given suffix.
   For example, if the mutable routine r belonged to a VM named "foo",
     jitter_mutable_routine_begin_class (ctx, r, "label")
   would open a class in the context ctx named "foo-label". */
static void
jitter_mutable_routine_begin_class (jitter_print_context ctx,
                                    const struct jitter_mutable_routine *p,
                                    const char *suffix)
{
  char *prefix = p->vm->configuration->lower_case_prefix;
  size_t size = strlen (prefix) + 1 + strlen (suffix) + 1;
  char *buffer = jitter_xmalloc (size);
  sprintf (buffer, "%s-%s", prefix, suffix);
  jitter_print_begin_class (ctx, buffer);
  free (buffer);
}

void
jitter_mutable_routine_print (jitter_print_context ctx,
                              const struct jitter_mutable_routine *r,
                              void *user_data)
{
  const bool slow_registers_only = r->options.slow_registers_only;
  const int instruction_no = jitter_mutable_routine_instruction_no (r);
  const struct jitter_instruction **ins
    = (const struct jitter_instruction **)
      jitter_dynamic_buffer_to_const_pointer (& r->instructions);

  /* We need to keep track of which instructions are jump targets.  If we
     already have the information, which is computed at specialization time,
     then use it; otherwise compute it now. */
  bool *is_target;
  if (r->stage >= jitter_routine_stage_specialized)
    is_target = r->jump_targets;
  else
    is_target = jitter_mutable_routine_jump_targets (r);

  /* Prepare a printf format string leaving the correct amount of space to align
     the first argument of every instruction to the same column.  The format
     string describes a single conversion specification, the instruction name as
     a string. */
  size_t max_instruction_name_length
    = jitter_maximum_instruction_name_length (r);
  size_t max_label_name_length
    = (/* "$L" */ 2
       + jitter_digit_no_radix_10 (instruction_no - 1)
       + /* ":" */ 1);
  int i;
  for (i = 0; i < instruction_no; i ++)
    {
      const struct jitter_instruction * in = ins [i];
      const struct jitter_meta_instruction * mi = in->meta_instruction;
      const struct jitter_parameter **ps
        = (const struct jitter_parameter **) in->parameters;

      bool newline_after_label = false; // FIXME: configuration parameter?
      int indentation_width = max_label_name_length + 1;
      int printed_char_no_for_this_line = 0;
      if (is_target [i])
        {
          /* It is okay to use "$L" followed by an unspecialized index as a
             label name; this way we have a guarantee that all label names are
             unique. */
          char label_name_buffer [100];
          sprintf (label_name_buffer, "$L%i", i);
          jitter_mutable_routine_begin_class (ctx, r, "label");
          jitter_print_char_star (ctx, label_name_buffer);
          jitter_print_end_class (ctx);
          jitter_mutable_routine_begin_class (ctx, r, "punctuation");
          jitter_print_char (ctx, ':');
          jitter_print_end_class (ctx);
          if (newline_after_label)
            jitter_print_char (ctx, '\n');
          else
            printed_char_no_for_this_line = strlen (label_name_buffer) + 1;
        }
      int j;
      for (j = printed_char_no_for_this_line; j < indentation_width; j ++)
        jitter_print_char (ctx, ' ');
      jitter_mutable_routine_begin_class (ctx, r, "instruction");
      jitter_print_char_star (ctx, mi->name);
      jitter_print_end_class (ctx);
      if (mi->parameter_no > 0)
        {
          int j;
          for (j = strlen (mi->name); j < max_instruction_name_length + 1; j ++)
            jitter_print_char (ctx, ' ');
        }
      const int arity = mi->parameter_no;
      for (j = 0; j < arity; j ++)
        {
          const struct jitter_parameter *p = ps [j];
          switch (p->type)
            {
            case jitter_parameter_type_uninitialized:
              jitter_mutable_routine_begin_class (ctx, r, "invalid");
              jitter_print_char_star (ctx, "<uninitialized>");
              jitter_print_end_class (ctx);
              break;
            case jitter_parameter_type_register_id:
              {
                int register_index = p->register_index;
                /* If the routine has been modified to use slow registers only,
                   unmodify it for printing: the modification simply consists in
                   changing register indices so that the first one maps to the
                   first slow register for each class. */
                const struct jitter_register_class *register_class
                  = mi->parameter_types [j].register_class;
                if (slow_registers_only)
                  register_index -= register_class->fast_register_no;
                /* Print the possibly unmodified register. */
                jitter_mutable_routine_begin_class (ctx, r, "register");
                jitter_print_char (ctx, '%');
                jitter_print_char (ctx, register_class->character);
                jitter_print_int (ctx, 10, register_index);
                jitter_print_end_class (ctx);
                break;
              }
            case jitter_parameter_type_literal:
              {
                const jitter_literal_parameter_printer printer
                  = mi->parameter_types [j].literal_printer;
                /* If the printer is the default printer than use the number
                   class; otherwise let the printer itself deal with classes. */
                if (printer == jitter_default_literal_parameter_printer)
                  jitter_mutable_routine_begin_class (ctx, r, "number");
                printer (ctx, p->literal.ufixnum, user_data);
                if (printer == jitter_default_literal_parameter_printer)
                  jitter_print_end_class (ctx);
                break;
              }
            case jitter_parameter_type_label:
              jitter_mutable_routine_begin_class (ctx, r, "label");
              jitter_print_char_star (ctx, "$L");
              jitter_print_long (ctx, 10, (long) p->label_as_index);
              jitter_print_end_class (ctx);
              break;
            default:
              /* Even if in the future I remove some parameter types this
                 default case remains useful for debugging.  Don't touch it. */
              jitter_mutable_routine_begin_class (ctx, r, "invalid");
              jitter_print_char_star (ctx, "<INVALID-ARGUMENT-TYPE>");
              jitter_print_end_class (ctx);
              break;
            } /* switch */
          if (j + 1 != arity)
            {
              jitter_mutable_routine_begin_class (ctx, r, "punctuation");
              jitter_print_char (ctx, ',');
              jitter_print_end_class (ctx);
              jitter_print_char (ctx, ' ');
            }
        } /* inner for: parameter loop. */
      jitter_print_char (ctx, '\n');
    } /* outer for: instruction loop. */

  /* If we have allocated the boolean array here then free it; if not then we
     were reusing some part of the routine, and of course we should not break
     it. */
  if (r->stage < jitter_routine_stage_specialized)
    free (is_target);
}




/* Label resolution.
 * ************************************************************************** */

void
jitter_mutable_routine_resolve_labels (struct jitter_mutable_routine *pr)
{
  if (pr->stage != jitter_routine_stage_unspecialized)
    jitter_fatal ("resolving unspecialized labels in non-unspecialized routine");

  const int instruction_no = jitter_mutable_routine_instruction_no (pr);
  struct jitter_instruction **ins
    = jitter_dynamic_buffer_to_pointer (& pr->instructions);

  /* Scan instructions sequentially, and for each of them scan parameters
     sequentially, replacing opaque labels with instruction indices.  This
     relies of parameters *not* being shared: each label parameter must be
     touched exactly once. */

  /* For every instruction... */
  int i;
  for (i = 0; i < instruction_no; i ++)
    {
      const struct jitter_instruction * in = ins [i];
      const struct jitter_meta_instruction * mi = in->meta_instruction;
      struct jitter_parameter **ps = in->parameters;

      /* ...For every instruction parameter... */
      const int arity = mi->parameter_no;
      int j;
      for (j = 0; j < arity; j ++)
        {
          struct jitter_parameter *p = ps [j];
          /* ...If the parameter is a label... */
          if (p->type == jitter_parameter_type_label)
            {
              /* Replace the label with its instruction index. */
              jitter_label label = p->label;
              jitter_int label_instruction_index
                = jitter_get_label_instruction_index (pr, label);
              if (label_instruction_index == -1)
                jitter_fatal ("undefined label %li", (long) label);

              /* Notice that this assignment invalidates p->label . */
              p->label_as_index = label_instruction_index;
            }
        }
    }
}
