This file contains an overview of the design of the compiler.
See also overall_design.html
for an overview of how the different sub-systems (compiler,
library, runtime, etc.) fit together.
OUTLINE
The main job of the compiler is to translate Mercury into C, although it
can also translate (subsets of) Mercury to some other languages: Goedel,
Mercury bytecode (for a planned bytecode interpreter), MSIL (for the
Microsoft .NET platform) and RL (the Aditi Relational Language).
The top-level of the compiler is in the file mercury_compile.m.
The basic design is that compilation is broken into the following
stages:
- 1. parsing (source files -> HLDS)
- 2. semantic analysis and error checking (HLDS -> annotated HLDS)
- 3. high-level transformations (annotated HLDS -> annotated HLDS)
- 4. code generation (annotated HLDS -> target representation)
- 5. low-level optimizations
(target representation -> target representation)
- 6. output code (target representation -> target code)
Note that in reality the separation is not quite as simple as that.
Although parsing is listed as step 1 and semantic analysis is listed
as step 2, the last stage of parsing actually includes some semantic checks.
And although optimization is listed as steps 3 and 5, it also occurs in
steps 2, 4, and 6. For example, elimination of assignments to dead
variables is done in mode analysis; middle-recursion optimization and
the use of static constants for ground terms is done in code
generation; and a few low-level optimizations are done in llds_out.m
as we are spitting out the C code.
In addition, the compiler is actually a multi-targeted compiler
with several different back-ends. When you take the different
back-ends into account, the structure looks like this:
- front-end
- 1. parsing (source files -> HLDS)
- 2. semantic analysis and error checking (HLDS -> annotated HLDS)
- 3. high-level transformations (annotated HLDS -> annotated HLDS)
- back-ends
- a. LLDS back-end
- 4a. code generation (annotated HLDS -> LLDS)
- 5a. low-level optimizations (LLDS -> LLDS)
- 6a. output code (LLDS -> C)
- b. MLDS back-end
- 4b. code generation (annotated HLDS -> MLDS)
- 5b. MLDS transformations (MLDS -> MLDS)
- 6b. output code
(MLDS -> C or MLDS -> MSIL
or eventually MLDS -> Java, etc.)
- c. RL back-end
- 4c. code generation (annotated HLDS -> RL)
- 5c. low-level optimizations (RL -> RL)
- 6c. output code (RL -> RL-bytecode)
- d. bytecode back-end
- 4d. code generation (annotated HLDS -> bytecode)
DETAILED DESIGN
This section describes the role of each module in the compiler.
For more information about the design of a particular module,
see the documentation at the start of that module's source code.
The action is co-ordinated from mercury_compile.m.
Option handling
The command-line options are defined in the module options.m.
mercury_compile.m calls library/getopt.m, passing the predicates
defined in options.m as arguments, to parse them. It then invokes
handle_options.m to postprocess the option set. The results are
stored in the io__state, using the type globals defined in globals.m.
FRONT END
1. Parsing
The result at this stage is the High Level Data Structure,
which is defined in four files:
- hlds_data.m defines the parts of the HLDS concerned with
function symbols, types, insts, modes and determinisms;
- hlds_goal.m defines the part of the HLDS concerned with the
structure of goals, including the annotations on goals;
- hlds_pred.m defines the part of the HLDS concerning
predicates and procedures;
- hlds_module.m defines the top-level parts of the HLDS,
including the type module_info.
The module hlds_out.m contains predicates to dump the HLDS to a file.
The module goal_util.m contains predicates for renaming variables
in an HLDS goal.
2. Semantic analysis and error checking
Any pass which can report errors or warnings must be part of this stage,
so that the compiler does the right thing for options such as
`--halt-at-warn' (which turns warnings into errors) and
`--error-check-only' (which makes the compiler only compile up to this stage).
- implicit quantification
-
quantification.m handles implicit quantification and computes
the set of non-local variables for each sub-goal.
It also expands away bi-implication (unlike the expansion
of implication and universal quantification, this expansion
cannot be done until after quantification).
This pass is called from the `transform' predicate in make_hlds.m.
- checking typeclass instances (check_typeclass.m)
-
check_typeclass.m both checks that instance declarations satisfy all
the appropriate superclass constraints and
performs a source-to-source transformation on the
methods methods from the instance declarations.
The transformed code is checked for type, mode, uniqueness, purity
and determinism correctness by the later passes, which has the effect
of checking the correctness of the instance methods themselves
(ie. that the instance methods match those expected by the typeclass
declaration).
During the transformation,
pred_ids and proc_ids are assigned to the methods for each instance.
In
addition, while checking that the superclasses of a class are satisfied
by the instance declaration, a set of constraint_proofs are built up
for the superclass constraints. These are used by polymorphism.m when
generating the base_typeclass_info for the instance.
- type checking
-
- typecheck.m handles type checking, overloading resolution &
module name resolution, and almost fully qualifies all predicate
and functor names. It sets the map(var, type) field in the
pred_info. However, typecheck.m doesn't figure out the pred_id
for function calls or calls to overloaded predicates; that can't
be done in a single pass of typechecking, and so it is done
later on (in post_typecheck.m, for both preds and function calls)
Typeclass constraints are checked here, and
any redundant constraints that are eliminated are recorded (as
constraint_proofs) in the pred_info for future reference. When it has
finished, typecheck.m calls clause_to_proc.m to make duplicate copies
of the clauses for each different mode of a predicate; all later
stages work on procedures, not predicates.
- type_util.m contains utility predicates dealing with types
that are used in a variety of different places within the compiler
- post_typecheck.m may also be considered to logically be a part
of typechecking, but it is actually called from purity
analysis (see below). It contains the stuff related to
type checking that can't be done in the main type checking pass.
It also removes assertions from further processing.
- assertions
-
assertion.m is the abstract interface to the assertion table.
Currently all the compiler does is type check the assertions and
record for each predicate that is used in an assertion, which
assertion it is used in. The set up of the assertion table occurs
in post_typecheck__finish_assertion.
- purity analysis
-
purity.m is responsible for purity checking, as well as
defining the
purity
type and a few public
operations on it. It also calls post_typecheck.m to
complete the handling of predicate
overloading for cases which typecheck.m is unable to handle,
and to check for unbound type variables.
Elimination of double negation is also done here; that needs to
be done after quantification analysis and before mode analysis.
- polymorphism transformation
-
polymorphism.m handles introduction of type_info arguments for
polymorphic predicates and introduction of typeclass_info arguments
for typeclass-constrained predicates.
This phase needs to come before mode analysis so that mode analysis
can properly reorder code involving existential types.
(It also needs to come before simplification so that simplify.m's
optimization of goals with no output variables doesn't do the
wrong thing for goals whose only output is the type_info for
an existentially quantified type parameter.)
This phase also
converts higher-order predicate terms into lambda expressions,
and copies the clauses to the proc_infos in preparation for
mode analysis.
The polymorphism.m module also exports some utility routines that
are used by other modules. These include some routines for generating
code to create type_infos, which are used by simplify.m and magic.m
when those modules introduce new calls to polymorphic procedures.
- mode analysis
-
- indexing and determinism analysis
-
- switch_detection.m transforms into switches those disjunctions
in which several disjuncts test the same variable against different
function symbols.
- cse_detection.m looks for disjunctions in which each disjunct tests
the same variable against the same function symbols, and hoists any
such unifications out of the disjunction.
If cse_detection.m modifies the code,
it will re-run mode analysis and switch detection.
- det_analysis.m annotates each goal with its determinism;
it inserts cuts in the form of "some" goals wherever the determinisms
and delta instantiations of the goals involved make it necessary.
Any errors found during determinism analysis are reported by
det_report.m.
Det_util.m contains utility predicates used in several modules.
- checking of unique modes (unique_modes.m)
-
unique_modes.m checks that non-backtrackable unique modes were
not used in a context which might require backtracking.
Note that what unique_modes.m does is quite similar to
what modes.m does, and unique_modes calls lots of predicates
defined in modes.m to do it.
- stratification checking
-
The module stratify.m implements the `--warn-non-stratification'
warning, which is an optional warning that checks for loops
through negation.
- simplification (simplify.m)
-
simplify.m finds and exploits opportunities for simplifying the
internal form of the program, both to optimize the code and to
massage the code into a form the code generator will accept.
It also warns the programmer about any constructs that are so simple
that they should not have been included in the program in the first
place. (That's why this pass needs to be part of semantic analysis:
because it can report warnings.)
simplify.m converts complicated unifications into procedure calls.
simplify.m calls common.m which looks for (a) construction unifications
that construct a term that is the same as one that already exists,
or (b) repeated calls to a predicate with the same inputs, and replaces
them with assignment unifications.
simplify.m also attempts to partially evaluate calls to builtin
procedures if the inputs are all constants (see const_prop.m),
3. High-level transformations
The first pass of this stage does tabling transformations (table_gen.m).
This involves the insertion of several calls to tabling predicates
defined in mercury_builtin.m and the addition of some scaffolding structure.
Note that this pass can change the evaluation methods of some procedures to
eval_table_io, so it should come before any passes that require definitive
evaluation methods (e.g. inlining).
The next pass of this stage is a code simplification, namely
removal of lambda expressions (lambda.m):
-
lambda.m converts lambda expressions into higher-order predicate
terms referring to freshly introduced separate predicates.
This pass needs to come after unique_modes.m to ensure that
the modes we give to the introduced predicates are correct.
It also needs to come after polymorphism.m since polymorphism.m
doesn't handle higher-order predicate constants.
(Is there any good reason why lambda.m comes after table_gen.m?)
The next pass is termination analysis. The various modules involved are:
-
termination.m is the control module. It sets the argument size and
termination properties of builtin and compiler generated procedures,
invokes term_pass1.m and term_pass2.m
and writes .trans_opt files and error messages as appropriate.
-
term_pass1.m analyzes the argument size properties of user-defined procedures,
-
term_pass2.m analyzes the termination properties of user-defined procedures.
-
term_traversal.m contains code common to the two passes.
-
term_errors.m defines the various kinds of termination errors
and prints the messages appropriate for each.
-
term_util.m defines the main types used in termination analysis
and contains utility predicates.
-
lp.m is used by term_pass1.m. It implements the Linear Programming
algorithm for optimizing a set of linear constraints with respect to
a linear cost function.
Most of the remaining HLDS-to-HLDS transformations are optimizations:
- specialization of higher-order and polymorphic predicates where the
value of the higher-order/type_info/typeclass_info arguments are known
(higher_order.m)
- attempt to introduce accumulators (accumulator.m). This optimizes
procedures whose tail consists of independent associative computations
or independant chains of commutative computations into a tail
recursive form by the introduction of accumulators. If lco is turned
on it can also transform some procedures so that only construction
unifications are after the recursive call. This pass must come before
lco, unused_args (eliminating arguments makes it hard to relate the
code back to the assertion) and inlining (can make the associative
call disappear).
- inlining (i.e. unfolding) of simple procedures (inlining.m)
- pushing constraints as far left as possible (constraint.m);
this does not yet work.
- deforestation and partial evaluation (deforest.m). This optimizes
multiple traversals of data structures within a conjunction, and
avoids creating intermediate data structures. It also performs
loop unrolling where the clause used is known at compile time.
deforest.m makes use of the following sub-modules
(`pd_' stands for "partial deduction"):
-
pd_cost.m contains some predicates to estimate the improvement
caused by deforest.m.
-
pd_debug.m produces debugging output.
-
pd_info.m contains a state type for deforestation.
-
pd_term.m contains predicates to check that the deforestation algorithm
terminates.
-
pd_util.m contains various utility predicates.
- issue warnings about unused arguments from predicates, and create
specialized versions without them (unused_args.m); type_infos are
often unused.
- unneeded_code.m looks for goals whose results are either not needed
at all, or needed in some branches of computation but not others. Provided
that the goal in question satisfies some requirements (e.g. it is pure,
it cannot fail etc), it either deletes the goal or moves it to the
computation branches where its output is needed.
- elimination of dead procedures (dead_proc_elim.m). Inlining, higher-order
specialization and the elimination of unused args can make procedures dead
even the user doesn't, and automatically constructed unification and
comparison predicates are often dead as well.
- conversion of Aditi procedures into disjunctive normal form (dnf.m).
The supplementary magic sets and context transformations are only defined
for predicates in DNF.
- supplementary magic sets or supplementary context transformation of
Aditi procedures (magic.m, magic_util.m, context.m).
The magic sets or context transformations must be applied to convert the
program to a form for which Aditi-RL bytecode can be generated.
- reducing the number of variables that have to be saved across
procedure calls (saved_vars.m). We do this by putting the code that
generates the value of a variable just before the use of that variable,
duplicating the variable and the code that produces it if necessary,
provided the cost of doing so is smaller than the cost of saving and
restoring the variable would be.
The module transform.m contains stuff that is supposed to be useful
for high-level optimizations (but which is not yet used).
a. LLDS BACK-END
4a. Code generation.
- pre-passes to annotate the HLDS
-
Before code generation there are a few more passes which
annotate the HLDS with information used for code generation:
- choosing registers for procedure arguments (arg_info.m)
-
Currently uses one of two simple algorithms, but
we may add other algorithms later.
- annotation of goals with liveness information (liveness.m)
-
This records the birth and death of each variable
in the HLDS goal_info.
- allocation of stack slots
-
This is done by live_vars.m, which works
out which variables need to be saved on the
stack when (trace.m determines what variables
are needed for debugging purposes).
It then uses graph_colour.m to determine
a good allocation of variables to stack slots.
- migration of builtins following branched structures
-
This transformation, which is performed by
follow_code.m, improves the results of follow_vars.
- allocating the follow vars (follow_vars.m)
-
Traverses backwards over the HLDS, annotating some
goals with information about what locations variables
will be needed in next. This allows us to generate
more efficient code by putting variables in the right
spot directly. This module is not called from
mercury_compile.m; it is called from store_alloc.m.
- allocating the store map (store_alloc.m)
-
Annotates each branched goal with variable location
information so that we can generate correct code
by putting variables in the same spot at the end
of each branch.
- computing goal paths (goal_path.m)
-
The goal path of a goal defines its position in
the procedure body. This transformation attaches
its goal path to every goal, for use by the debugger.
- code generation
-
Code generation converts HLDS into LLDS.
For the LLDS back-end, this is also the point at which we
insert code to handle debugging and trailing, and to do
heap reclamation on failure.
The main code generation module is code_gen.m.
It handles conjunctions and negations, but calls sub-modules
to do most of the other work:
- ite_gen.m (if-then-elses)
- call_gen.m (predicate calls and also calls to
out-of-line unification procedures)
- disj_gen.m (disjunctions)
- par_conj.m (parallel conjunctions)
- unify_gen.m (unifications)
- switch_gen.m (switches), which has sub-modules
- dense_switch.m
- lookup_switch.m
- string_switch.m
- tag_switch.m
- switch_util.m (also used by MLDS back-end)
- commit_gen.m (commits)
- pragma_c_gen.m (embedded C code)
It also calls middle_rec.m to do middle recursion optimization.
The code generation modules make use of
- code_info.m
-
The main data structure for the code generator.
- code_exprn.m
-
This defines the exprn_info type, which is
a sub-component of the code_info data structure
which holds the information about
the contents of registers and
the values/locations of variables.
- exprn_aux.m
-
Various preds which use exprn_info.
- code_util.m
-
Some miscellaneous preds used for code generation.
- code_aux.m
-
Some miscellaneous preds which, unlike those in
code_util, use code_info.
- continuation_info.m
-
For accurate garbage collection, collects
information about each live value after calls,
and saves information about procedures.
- trace.m
-
Inserts calls to the runtime debugger.
- code generation for `pragma export' declarations (export.m)
- This is handled seperately from the other parts of code generation.
mercury_compile.m calls the procedures `export__produce_header_file'
and `export__get_pragma_exported_procs' to produce C code fragments
which declare/define the C functions which are the interface stubs
for procedures exported to C.
- generation of constants for RTTI data structures
- This could also be considered a part of code generation,
but for the LLDS back-end this is currently done as part
of the output phase (see below).
The result of code generation is the Low Level Data Structure (llds.m),
which may also contains some data structures whose types are defined in rtti.m.
The code for each procedure is generated as a tree of code fragments
which is then flattened (tree.m).
5a. Low-level optimization (LLDS).
The various LLDS-to-LLDS optimizations are invoked from optimize.m.
They are:
- optimization of jumps to jumps (jumpopt.m)
- elimination of duplicate code sequences (dupelim.m)
- optimization of stack frame allocation/deallocation (frameopt.m)
- filling branch delay slots (delay_slot.m)
- dead code and dead label removal (labelopt.m)
- peephole optimization (peephole.m)
- value numbering
This is done by value_number.m, which has the following sub-modules:
- vn_block.m
-
Traverse an extended basic block, building up tables showing
the actions that must be taken, and the current and desired
contents of locations.
- vn_cost.m
-
Computes the cost of instruction sequences.
Value numbering should never replace an instruction
sequence with a more expensive sequence. Unfortunately,
computing costs accurately is very difficult.
- vn_debug.m
-
Predicates to dump data structures used in value
numbering.
- vn_filter.m
-
Module to eliminate useless temporaries introduced by
value numbering. Not generating them in the first place
would be better, but would be quite difficult.
- vn_flush.m
-
Given the tables built up by vn_block and a list of nodes
computed by vn_order, generate code to assign the required
values to each temporary and live location in what is
hopefully the fastest and most compact way.
- vn_order.m
-
Given tables built up by vn_block showing the actions that
must be taken, and the current and desired contents of
locations, find out which shared subexpressions should
have temporaries allocated to them and in what order these
temporaries and the live locations should be assigned to.
This module uses the module atsort.m to perform an approximate
topological sort on the nodes of the location dependency
graph it operations on (since the graph may have cycles,
a precise topological sort may not exist).
- vn_table.m
-
Abstract data type showing the current and desired
contents of locations.
- vn_temploc.m
-
Abstract data type to keep track of the availability
of registers and temporaries.
- vn_type.m
-
This module defines the types used by the other
modules of the value numbering optimization.
- vn_util.m
-
Utility predicates.
- vn_verify.m
-
Sanity checks to make sure that (a) the optimized code
computes the same values as the original code, and (b)
the optimized code does not dereference tagged pointers
until the tag is known. (Violations of (b) usually cause
unaligned accesses, which cause bus errors on many machines.)
Several of these modules (and also frameopt, above) use livemap.m,
which finds the set of locations live at each label.
Depending on which optimization flags are enabled,
optimize.m may invoke many of these passes multiple times.
Some of the low-level optimization passes use basic_block.m,
which defines predicates for converting sequences of instructions to
basic block format and back, as well as opt_util.m, which contains
miscellaneous predicates for LLDS-to-LLDS optimization.
6a. Output C code
- type_ctor_info.m generates the type_ctor_gen_info structures that list
items of information (including unification, index and compare predicates)
associated with each declared type constructor that go into the static
type_ctor_info data structure. If the type_ctor_gen_info structure is not
eliminated as inaccessible, this module adds the corresponding type_ctor_info
structure to the RTTI data structures defined in rtti.m,
which are part of the LLDS.
- base_typeclass_info.m generates the base_typeclass_info structures that
list the methods of a class for each instance declaration. These are added to
the RTTI data structures, which are part of the LLDS.
- stack_layout.m generates the stack_layout structures for
accurate garbage collection. Tables are created from the data
collected in continuation_info.m.
Stack_layout.m uses prog_rep.m and static_term.m to generate representations
of procedure bodies for use by the declarative debugger.
- Type_ctor_info structures and stack_layout structures both contain
pseudo_type_infos, which are type_infos with holes for type variables;
these are generated by pseudo_type_info.m.
- llds_common.m extracts static terms from the main body of the LLDS, and
puts them at the front. If a static term originally appeared several times,
it will now appear as a single static term with multiple references to it.
- transform_llds.m is responsible for doing any source to source
transformations on the llds which are required to make the C output
acceptable to various C compilers. Currently computed gotos can have
their maximum size limited to avoid a fixed limit in lcc.
- Final generation of C code is done in llds_out.m, which subcontracts the
output of RTTI structures to rtti_out.m.
b. MLDS BACK-END
The original LLDS code generator generates very low-level code,
since the LLDS was designed to map easily to RISC architectures.
We're currently developing a new back-end that generates much higher-level
code, suitable for generating Java, high-level C, etc.
This back-end uses the Medium Level Data Structure (mlds.m) as its
intermediate representation.
3b. pre-passes to annotate/transform the HLDS
Before code generation there is a pass which annotates the HLDS with
information used for code generation:
- mark_static_terms.m marks construction unifications
which can be implemented using static constants rather
than heap allocation.
For the MLDS back-end, we've tried to keep the code generator simple.
So we prefer to do things as HLDS to HLDS transformations where possible,
rather than complicating the HLDS to MLDS code generator.
So we have a pass which transforms the HLDS to handle trailing:
- add_trail_ops.m inserts code to manipulate the trail,
in particular ensuring that we apply the appropriate
trail operations before each choice point, when execution
resumes after backtracking, and whenever we do a commit.
The trail operations are represented as (and implemented as)
calls to impure procedures defined in library/private_builtin.m.
4b. MLDS code generation
- ml_code_gen.m converts HLDS code to MLDS.
The following sub-modules are used to handle different constructs:
- ml_unify_gen.m
- ml_call_gen.m
- ml_switch_gen.m, which in turn has sub-modules
- ml_dense_switch.m
- ml_string_switch.m
- ml_tag_switch.m
- switch_util.m (also used by MLDS back-end)
The module ml_code_util.m provides utility routines for
MLDS code generation. The module ml_util.m provides some
general utility routines for the MLDS.
- ml_type_gen.m converts HLDS types to MLDS.
- type_ctor_info.m and base_typeclass_info.m generate
the RTTI data structures defined in rtti.m and pseudo_type_info.m
(those four modules are shared with the LLDS back-end)
and then mlds_to_rtti.m converts these to MLDS.
5b. MLDS transformations
- ml_tailcall.m annotates the MLDS with information about tailcalls.
- ml_optimize.m does MLDS->MLDS optimizations
- ml_elim_nested.m transforms the MLDS to eliminate nested functions.
6b. MLDS output
There are currently two backends that generate code from MLDS, one
generates C/C++ code, the other generates Microsoft's Intermediate
Language (MSIL or IL).
- mlds_to_c.m converts MLDS to C/C++ code.
The MLDS->IL backend is broken into several submodules.
- mlds_to_ilasm.m converts MLDS to IL assembler and writes it to a .il file.
- mlds_to_il.m converts MLDS to IL
- ilds.m contains representations of IL
- ilasm.m contains output routines for writing IL to assembler.
- il_peephole.m performs peephole optimization on IL instructions.
After IL assembler has been emitted, ILASM in invoked to turn the .il
file into a .dll or .exe.
c. Aditi-RL BACK-END
4c. Aditi-RL generation
- rl_gen.m converts HLDS to RL.
- rl_relops.m generates RL for relational operations such as joins.
- rl_info.m defines a state type.
- rl.m defines the the representation of Aditi-RL used within the
Mercury compiler. There are some slight differences between rl.m
and Aditi-RL to make optimization easier.
- rl_dump.m contains predicates to write the types defined in rl.m.
5c. Aditi-RL optimization
- rl_opt.m invokes the RL optimization passes.
- rl_block.m converts an RL procedure into basic blocks, and performs
other tasks such as detecting the loops in those basic blocks.
- rl_analyse.m contains a generic data-flow analysis procedure for
RL procedures.
- rl_liveness.m uses rl_analyse.m to insert code to initialise relations
and clear references to them when they are no longer needed.
- rl_loop.m moves invariants out of loops.
- rl_block_opt.m performs common subexpression elimination and instruction
merging on basic blocks.
- rl_key.m computes upper and lower bounds on the non-locals of a goal
for which the goal could succeed, which is useful for determining when
an index could be used for a relational operation.
- rl_sort.m introduces sort-merge and indexed versions of relational
operations where possible, and optimizes away unnecessary sorting and
indexing.
- rl_stream.m detects relations which do not need to be materialised.
6c. Output Aditi-RL code
- rl_out.m converts from the instructions defined in rl.m
to bytecode either as data in the <module>.c file or
to <module>.rlo and outputs a text representation to
<module>.rla.
- rl_exprn.m is called from rl_out.m to convert top down Mercury
code (in HLDS form) to Aditi bytecode.
- rl_code.m contains the definition of the bytecodes interpreted
by Aditi. This file is automatically generated from the Aditi sources.
- rl_file.m contains routines to output the bytecodes defined in rl_code.m.
d. BYTECODE BACK-END
The Mercury compiler can translate Mercury programs into bytecode for
interpretation by a bytecode interpreter. The intent of this is to
achieve faster turn-around time during development. However, the
bytecode interpreter has not yet been written.
- bytecode.m defines the internal representation of bytecodes, and contains
the predicates to emit them in two forms. The raw bytecode form is emitted
into <filename>.bytecode for interpretation, while a human-readable
form is emitted into <filename>.bytedebug for visual inspection.
- bytecode_gen.m contains the predicates that translate HLDS into bytecode.
- bytecode_data.m contains the predicates that translate ints, strings
and floats into bytecode. This is also used by rl_code.m.
MISCELLANEOUS
- builtin_ops:
-
This module defines the types unary_op and binary_op
which are used by several of the different back-ends:
bytecode.m, llds.m, and mlds.m.
- c_util:
-
This module defines utility routines useful for generating
C code. It is used by both llds_out.m and mlds_to_c.m.
- det_util:
-
This module contains utility predicates needed by the parts
of the semantic analyzer and optimizer concerned with
determinism.
- special_pred.m, unify_proc.m:
-
These modules contain stuff for handling the special
compiler-generated predicates which are generated for
each type: unify/2, compare/3, and index/1 (used in the
implementation of compare/3).
- dependency_graph.m:
-
This contains predicates to compute the call graph for a
module, and to print it out to a file.
(The call graph file is used by the profiler.)
The call graph may eventually also be used by det_analysis.m,
inlining.m, and other parts of the compiler which could benefit
from traversing the predicates in a module in a bottom-up or
top-down fashion with respect to the call graph.
- passes_aux.m
-
Contains code to write progress messages, and higher-order
code to traverse all the predicates defined in the current
module and do something with each one.
- opt_debug.m:
-
Utility routines for debugging the LLDS-to-LLDS optimizations.
- error_util.m:
-
Utility routines for printing nicely formatted error messages.
CURRENTLY USELESS
The following modules do not serve any function at the moment.
Some of them are obsolete; other are work-in-progress.
(For some of them its hard to say which!)
- excess.m:
-
This eliminates assignments that merely introduce another
name for an already existing variable. The functionality of
this module has been included in simplify.m, however sometime
in the future it may be necessary to provide a version which
maintains superhomogeneous form.
- lco.m:
-
This finds predicates whose implementations would benefit
from last call optimization modulo constructor application.
It does not apply the optimization and will not until the
mode system is capable of expressing definite aliasing.
- mercury_to_goedel.m:
-
This converts from item_list to Goedel source code.
It works for simple programs, but doesn't handle
various Mercury constructs such as lambda expressions,
higher-order predicates, and functor overloading.
Last update was $Date: 2001/01/19 01:50:32 $ by $Author: zs $@cs.mu.oz.au.