Table of Contents

Name

snoot - translate pre-processed C to SUIF

Synopsis

snoot [ options ] infile outfile

Description

The snoot program is the core of the SUIF C front end. It translates from pre-processed ANSI-C to SUIF. The SUIF code that snoot produces is non-standard, however; it must be passed through porky with the -defaults flag before it becomes standard SUIF that other passes can handle.

The entire C front-end for SUIF consists of three passes. First, cpp, the ANSI-C pre-processor. This is not included with SUIF. Any standard ANSI-C pre-processor may be used; the gnu C pre-processor that is included with gcc is one option. The output of cpp is then fed into snoot. The output from snoot is the first SUIF file. Then the last stage is porky with the -defaults option. Together, these three passes turn ANSI-C into standard SUIF.

Options

-W
Turn on more warning messages. By default, only important warnings are displayed. If used a second time, all possible warnings are issued.
-w
Suppress all warning messages. This overrides the -W option.
-keep-comments
Save all comments from the C code as C comment" annotations on SUIF ``mrk'' instructions. By default, comments are ignored.

Note that for this to have any effect, the C comments must have been preserved by the C pre-processor; by default cpp throws them away before snoot even sees the code. Use the -C option for cpp to save comments in the pre-processing stage.

-ignore-comments
Do not save C comments. This is the default. If both -keep-comments and -ignore-comments are specified, the one that occurs latest on the command line takes effect.
-x
Write cross-reference of symbol uses as source references annotations on the SUIF symbols. The location of each reference in the source file is recorded.
-P
Print function prototypes and global variable declarations to standard error. This output can be appended to the top of a source file so that the next time it's compiled more type checking can be done.
-sdensity
Set the density of labels used as a cutoff for using SUIF mbr instructions instead of individual comparisons for switch statements. The density is interpreted as a floating point value. The default is 0.5, meaning that at least half the values in a range have to have case labels before an mbr instruction is used.
-en
Set the maximum number of error messages snoot will issue before giving up. The default is 20. Ordinarily, snoot will issue an error message and continue to look for more errors. Even if the rest of the program can successfully be translated, snoot will still return an error code. Once the limit is reached, snoot assumes that it is so hopelessly confused by earlier errors that there's no point in reporting any more.
-mark-execution-points
Put sequence point annotations in the SUIF code corresponding to sequence points in the source code, when possible. Temporary values will be spilled into new variables if necessary. The one situation where sequence points are not properly inserted is for C ``for()'' statements that are translated into SUIF TREE_FOR nodes. There is no place on a SUIF TREE_FOR to put the sequence point that comes between evaluation of the incrementing expression and the test expression.

Sequence points are defined in the ANSI C standard as points in the execution where some things are guaranteed to have already been executed and others not yet executed. The standard defines exactly where they occur. The option of marking these in the SUIF code is provided in case later passes want to use them to print traces of variable values or something of that sort.

-ignore-execution-points
Do not mark sequence points in the SUIF code. This is the default. If both -mark-execution-points and -ignore-execution-points are specified, the one that occurs latest on the command line takes effect.
-null-check
Insert code to check at runtime for a NULL pointer every time memory is explicitly read or written in the C code (i.e. for every use of the ``[]'', ``->'', or unary ``*'' operators). If a NULL pointer is found, an error message is issued giving the source line number and file and the program aborts.
-no-null-check
Do not insert code to check at runtime for NULL pointers. This is the default. If both -nullcheck and -no-null-check are specified, the one that occurs latest on the command line takes effect.
-Ttarget-name
Use the system-specific target parameters specified by target-name in compilation. This is used in cross-compilation or to generate code for a different back-end C compiler. The parameters include such things as the byte order of the machine, the sizes of the various types, and whether the type ``char'' is signed or unsigned. The default is to use the parameters from the C compiler used to build snoot (typically gcc).

To see a list of targets snoot understands, type snoot -T-. Target information is stored in the snoot source file config.h. See the snoot source file find_params.c for information on generating target information for new systems.

-keep-typedef-info
Create dummy variables to represent typedef names. The dummy variables are given type ``int'' and have typedef name annotations attached. The data on the annotation contains an immed list with one item, the type of the typedef.
-builtin builtin-name
Consider builtin-name to be a built-in identifier. That means that builtin-name can be used as a variable or followed by arguments in parentheses and each such expression will be translated to a SUIF generic instruction with builtin-name as its name. Within the parentheses can be a comma-separated argument list, where each argument can be a type, a string literal, or an expression. These generic instructions will be passed through most SUIF passes and s2c will translate them back into a form similar to their form in the original source code. This can be used to implement asm() directives, or built-in identifiers used for vararg macros in headers for some systems. Note that an alternative to specifying built-in identifiers on the commandline with this switch is to specify them in the configuration file config.h".
-force-enum-is-int
Force all enum types to use type ``int'' as their equivalent type. Ordinarily, enum types are mapped to the smallest integer type that can contain all their enumeration constants. This option overrides that for compatibility, since some programs assume that the compiler maps enums only to ``int'' under all circumstances.

History

The first ANSI-C front-end for SUIF was snout, written by Robert French. It was based on lcc, a portable C frontend with a code-generation interface (see ``A Code Generation Interface for ANSI C'' by Fraser and Hanson). Since the back-end interface provided by lcc is too low-level for SUIF, some substantial changes were made in various levels of lcc code and data-structures to preserve more information when generating SUIF code.

When the SUIF system was overhauled, Todd Smith rewrote the SUIF-specific parts of snout to create snoot for new SUIF. When more changes were made to SUIF that required more information to be preserved that lcc was losing early-on, Chris Wilson rewrote snoot. Various internal transformations and datastructures used by lcc were removed. Now the front-end of lcc is used to generate SUIF code directly.

Table of Contents