Grammar Nazi strikes! :-)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48722 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2008-03-24 05:55:54 +00:00
parent a582f404df
commit ae851b63af

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@ -7,56 +7,55 @@ making it more configurable and useful.
Motivation
==========
As it stands, current version of LLVMC does not meet its stated goals
of configurability and extensibility and is therefore not used
much. The need for enhancements in LLVMC is also reflected in [1]_. The
As it stands, the current version of LLVMC does not meet its stated goals
of configurability and extensibility, and is therefore not used
much. The need for enhancements to LLVMC is also reflected in [1]_. The
proposed rewrite will fix the aforementioned deficiences and provide
an extensible, future-proof solution.
Design
======
A compiler driver's job is essentially to find a way how to transform
a set of input files into a set of targets, depending on the
user-provided options. Since several ways of transformation can exist
potentially, it's natural to use a directed graph to represent all of
them. In this graph, nodes are tools (for example, ``gcc -S`` is a tool
that generates assembly from C language files) and edges between them
mean that the output of one tool can be given as input to another (as
in ``gcc -S -o - file.c | as``). We'll call this graph the compilation
graph.
A compiler driver's job is essentially to find a way to transform a set
of input files into a set of targets, depending on the user-provided
options. Since several methods of transformation can potentially exist,
it's natural to use a directed graph to represent all of them. In this
graph, nodes are tools -- e.g., ``gcc -S`` is a tool that generates
assembly from C language files -- and edges between the nodes indicate
that the output of one tool can be given as input to another -- i.e.,
``gcc -S -o - file.c | as``. We'll call this graph the compilation graph.
The proposed design revolves around the compilation graph and the
following core abstractions:
- Target - An (intermediate) compilation target.
- Action - A shell command template that represents basic compilation
transformation(example: ``gcc -S $INPUT_FILE -o $OUTPUT_FILE``).
- Action - A shell command template that represents a basic compilation
transformation -- example: ``gcc -S $INPUT_FILE -o $OUTPUT_FILE``.
- Tool - Encapsulates information about a concrete tool used in the
compilation process, produces Actions. Operation depends on
compilation process, produces Actions. Its operation depends on
command-line options provided by the user.
- GraphBuilder - Constructs the compilation graph, operation depends
on command-line options.
- GraphBuilder - Constructs the compilation graph. Its operation
depends on command-line options.
- GraphTraverser - Traverses the compilation graph and constructs a
sequence of Actions needed to build the target file, operation
sequence of Actions needed to build the target file. Its operation
depends on command-line options.
A high-level view of the compilation process:
1. Configuration libraries (see below) are loaded in and the
compilation graph is constructed from the tool descriptions.
compilation graph is constructed from the tool descriptions.
2. Information about possible options is gathered from (the nodes of)
the compilation graph.
the compilation graph.
3. Options are parsed based on data gathered in step 2.
4. A sequence of Actions needed to build the target is constructed
using the compilation graph and provided options.
using the compilation graph and provided options.
5. The resulting action sequence is executed.
@ -65,8 +64,8 @@ Extensibility
To make this design extensible, TableGen [2]_ will be used for
automatic generation of the Tool classes. Users wanting to customize
LLVMC will need to write a configuration library consisting of a set
of TableGen descriptions of compilation tools plus a number of hooks
LLVMC need to write a configuration library consisting of a set of
TableGen descriptions of compilation tools plus a number of hooks
that influence compilation graph construction and traversal. LLVMC
will have the ability to load user configuration libraries at runtime;
in fact, its own basic functionality will be implemented as a
@ -76,7 +75,7 @@ TableGen specification example
------------------------------
This small example specifies a Tool that converts C source to object
files. Note that it is only a mock-up of inteded functionality, not a
files. Note that it is only a mock-up of intended functionality, not a
final specification::
def GCC : Tool<
@ -192,15 +191,15 @@ mock-up)::
Option handling
===============
Since one of the main tasks of the compiler driver is to correctly
Because one of the main tasks of the compiler driver is to correctly
handle user-provided options, it is important to define this process
in exact way. The intent of the proposed scheme is to function as a
drop-in replacement for GCC.
in an exact way. The intent of the proposed scheme is to function as
a drop-in replacement for GCC.
Option syntax
-------------
Option syntax is specified by the following formal grammar::
The option syntax is specified by the following formal grammar::
<command-line> ::= <option>*
<option> ::= <positional-option> | <named-option>
@ -211,20 +210,20 @@ Option syntax is specified by the following formal grammar::
<option-argument> ::= <string>
This roughly corresponds to the GCC option syntax. Note that grouping
of short options(as in ``ls -la``) is forbidden.
of short options (as in ``ls -la``) is forbidden.
Example::
llvmc -O3 -Wa,-foo,-bar -pedantic -std=c++0x a.c b.c c.c
Option arguments can also have special forms: for example, an argument
Option arguments can also have special forms. For example, an argument
can be a comma-separated list (like in -Wa,-foo,-bar). In such cases,
it's up to the option handler to parse the argument.
Option semantics
----------------
According to their meaning, options are classified into following
According to their meaning, options are classified into the following
categories:
- Global options - Options that influence compilation graph
@ -233,19 +232,19 @@ categories:
- Local options - Options that influence one or several Actions in
the generated action sequence. Example: -O3 (turn on optimization).
- Prefix options - Options that influence meaning of the following
- Prefix options - Options that influence the meaning of the following
command-line arguments. Example: -x language (specify language for
the input files explicitly). Prefix options can be local or global.
- Built-in options - Options that are hard-coded into
- Built-in options - Options that are hard-coded into the
driver. Examples: --help, -o file/-pipe (redirect output). Can be
local or global.
Naming
======
Since the compiler driver, as a single point of access to the LLVM
tool set, is a very often used tool, it would be desirable to make its name
Because the compiler driver, as a single point of access to the LLVM
tool set, is a frequently used tool, it is desirable to make its name
as short and easy to type as possible. Some possible names are 'llcc' or
'lcc', by analogy with gcc.