Amsterdam, The Netherlands
.PP
This document specifies the implementation-defined behaviour of the ANSI-C
-front end of the Amsterdam Compiler Kit as required by ANS X3.159-1989. Since
+front end of the Amsterdam Compiler Kit as required by ANS X3.159-1989. Since
the implementation-defined behaviour sometimes depends on the machine
compiling on or for, some items will be left unspecified in this
document\(dg.
The compiler assumes that it runs on a UNIX system.
.NS A.6.3.1
.IP -
-Diagnostics are placed on the standard error output. They have the
+Diagnostics are placed on the standard error output. They have the
following specification:
.br
"<file>", line <nr>: [(<class>)] <diagnostic>
When the class is "error", the <class> is absent.
.br
The class "strict" is used for violations of the standard which are
-not severe enough to stop compilation. An example is the the occurrence
+not severe enough to stop compilation. An example is the the occurrence
of non white-space after an '#else' or '#endif' pre-processing
-directive. The class "warning" is used for legal but dubious
-constructions. An example is overflow of constant expressions.
+directive. The class "warning" is used for legal but dubious
+constructions. An example is overflow of constant expressions.
.NS A.6.3.2
.IP -
-The function 'main' can have two arguments. The first argument is an
-integer specifying the number of arguments on the command line. The second
+The function 'main' can have two arguments. The first argument is an
+integer specifying the number of arguments on the command line. The second
argument is a pointer to an array of pointers to the arguments (as
strings).
.IP -
Interactive devices are terminals.
.NS A.6.3.3
.IP -
-The number of significant characters is an option. By default it is 64.
+The number of significant characters is an option. By default it is 64.
There is a distinction between upper and lower case.
.NS A.6.3.4
.IP -
.NS A.6.3.5
.IP -
The compiler assumes that it works on and compiles for a
-2-complement binary-number system. Shorts will use 2 bytes and longs
-will use 4 bytes. The size of integers are machine dependent.
+2-complement binary-number system. Shorts will use 2 bytes and longs
+will use 4 bytes. The size of integers are machine dependent.
.IP -
Converting an integer to a shorter signed integer is implemented by
ignoring the high-order byte(s) of the former.
Converting a unsigned integer to a signed integer of the same type is
-only done in administration. This means that the bit-pattern remains
+only done in administration. This means that the bit-pattern remains
unchanged.
.IP -
The result of bitwise operations on signed integers are what can be
be represented.
.NS A.6.3.7
.IP -
-The type returned by the sizeof-operator is 'unsigned int'. This is done
-for backward compatibility reasons.
+The type returned by the sizeof-operator (also known as size_t)
+is 'unsigned int'. This is done for backward compatibility reasons.
.IP -
Casting an integer to a pointer or vice versa has no effect in
-bit-pattern when the sizes are equal. Otherwise the value will be
+bit-pattern when the sizes are equal. Otherwise the value will be
truncated or zero-extended (depending on the direction of the
conversion and the relative sizes).
.IP -
When a pointer is as large as an integer, the type of a 'ptrdiff_t' will
-be 'int'. Otherwise the type will be 'long'.
+be 'int'. Otherwise the type will be 'long'.
.NS A.6.3.8
.IP -
Since the front end has only limited control over the registers, it can
only make it more likely that variables that are declared as
-registers also end up in registers. The only things that can possibly be
+registers also end up in registers. The only things that can possibly be
put into registers are : 'int', 'long', 'float', 'double', 'long double'
and pointers.
.NS A.6.3.9
.IP -
When a member of a union object is accessed using a member of a
-different type, the resulting value will usually be garbage. The
+different type, the resulting value will usually be garbage. The
compiler makes no effort to catch these errors.
.IP -
-The alignment of types is a compile-time option. The alignment of
-a structure-member is the alignment of its type. Usually, the
-alignment is passed on to the compiler by the 'ack' program. When a
+The alignment of types is a compile-time option. The alignment of
+a structure-member is the alignment of its type. Usually, the
+alignment is passed on to the compiler by the 'ack' program. When a
user wants to do this manually, he/she should be prepared for trouble.
.IP -
-A "plain" 'int' bit-field is taken as a 'signed int'. This means that
+A "plain" 'int' bit-field is taken as a 'signed int'. This means that
a field with a size 1 bit can only store the values 0 and -1.
.IP -
-The order of allocation of bit-fields is a compile-time option. By
+The order of allocation of bit-fields is a compile-time option. By
default, high-order bits are allocated first.
.IP -
An enum has the same size as a "plain" 'int'.
.NS A.6.3.10
.IP -
An access to a volatile declared variable is done by just mentioning
-the variable. E.g. the statement "x;" where x is declared volatile,
+the variable. E.g. the statement "x;" where x is declared volatile,
constitutes an access.
.S A.6.3.11
.IP -
a single character constant in a conditional-inclusion directive
matches the same value in the execution character set.
.IP -
-The pre-processor recognizes -I... command-line options. The
-directories thus specified are searched first. After that, depending on the
+The pre-processor recognizes -I... command-line options. The
+directories thus specified are searched first. After that, depending on the
command that the preprocessor is called with, machine/system-dependant
-directories are searched. After that, ~em/include/_tail_ac and
+directories are searched. After that, ~em/include/_tail_ac and
/usr/include are visited.
.IP -
Quoted names are first looked for in the directory in which the file
defined.
.NS A.6.3.14
.IP -
-NULL is defined as ((void *)0). This in order to flag dubious
+NULL is defined as ((void *)0). This in order to flag dubious
constructions like "int x = NULL;".
.IP -
The diagnostic printed by 'assert' is as follows:
.TE
.KE
As an addition, there is an isascii() macro, which tests whether a character
-is an ascii character. Characters in the range from \e000 to \e177 are ascii
+is an ascii character. Characters in the range from \e000 to \e177 are ascii
characters.
.KS
.IP -
argument is 0.0.
.IP -
The set of signals for the signal() function depends on the UNIX-system
-which the compiler is compiling for. The default handling, semantics
+which the compiler is compiling for. The default handling, semantics
and behaviour of these signals are those specified by the operating
-system vendor. The default handling is not reset when SIGILL is
+system vendor. The default handling is not reset when SIGILL is
received.
.IP -
A text-stream need not end in a new-line character.
A file can be open multiple times.
.IP -
When a remove() is done on an open file, reading and writing behave
-just as can be expected from a non-removed file. When the associated
+just as can be expected from a non-removed file. When the associated
stream is closed, all written data will be lost.
.IP -
When a file exists prior to a call to rename(), the behaviour is that
-of the underlying UNIX system. Normally, the call would fail.
+of the underlying UNIX system. Normally, the call would fail.
.IP -
The %p conversion in fprintf() has the same effect as %#x or %#lx,
depending on the sizes of pointer and integer.
depending on the sizes of pointer and integer.
.IP -
A - character that is neither the first nor the last character in the
-scanlist for %[ conversion is taken to be a range indicator. When the
+scanlist for %[ conversion is taken to be a range indicator. When the
first character has a higher ASCII-value than the second, the - will
just be put into the scanlist.
.IP -
When the requested size is zero, malloc(), calloc() and realloc()
return a null-pointer.
.IP -
-When abort() is called, output buffers will be flushed. Temporary files
+When abort() is called, output buffers will be flushed. Temporary files
(made with the tmpfile() function) will have disappeared when SIGABRT
is not caught or ignored.
.IP -
.br
The argument to putenv() is stored in an internal table, so malloc'ed
strings can not be freed until another call to putenv() (which sets the
-same environment variable) is made. The function returns 1 if it fails,
+same environment variable) is made. The function returns 1 if it fails,
0 otherwise.
.LP
.IP -
.TE
everything else causes strerror() to return "unknown error"
.IP -
-The local time zone is per default MET (GMT + 1:00:00). This can be
+The local time zone is per default MET (GMT + 1:00:00). This can be
changed through the TZ environment variable, or by some changes in the
sources.
.IP -
.TS
box;
l l l l l.
-ADDR STACK from proc sfit
-COERCIONS STACKINGRULES gen reg_any test
-INSTRUCTIONS TESTS highw reg_float to
-INT TIMEFACTOR inreg reg_loop ufit
-MOVES TOKENS is_rom reg_pointer uses
-PATTERNS call kills regvar with
-PROPERTIES cost leaving return yields
-REGISTERS defined loww reusing
-SETS exact move rom
-SIZEFACTOR example pat samesign
+ADDR STACKINGRULES gen proc test
+COERCIONS TESTS highw reg_any to
+INSTRUCTIONS TIMEFACTOR inreg reg_float topeltsize
+INT TOKENS is_rom reg_loop ufit
+MOVES call kills reg_pointer uses
+PATTERNS cost lab regvar with
+PROPERTIES defined labeldef return yields
+REGISTERS exact leaving reusing
+SETS example loww rom
+SIZEFACTOR fallthrough move samesign
+STACK from pat sfit
.TE
C style comments are accepted.
.DS
.I t
is omitted reg_any is assumed.
Undefined if inreg(\fIe\fP)<=0 .
+.LP
+The next two `functions' are only needed in a table that
+uses the top element size information.
+.IP topeltsize($a) 16
+Returns the size of the element on top of the EM-stack at the label
+identified by $a. This can be used to put the top of the stack in a
+register at the moment of an unconditional jump. At an unconditional jump,
+the size of the top-element will always look 0.
+.IP fallthrough($a)
+Returns 1 if the label identified by $a can be reached via fallthrough, 0
+otherwise.
.NH 2
Token descriptions
.PP
but patterns longer than three EM instructions are luckily not needed
too often.
.PP
+The EM mnemonic may also be the pseudo-instruction \fBlab\fP, which matches
+a label. Its argument can be used in testing on topeltsize and
+fallthrough. When this pattern is specified, the label should be defined
+explicitly with a
+.I labeldef
+statement.
+.PP
Following the EM-pattern there may be more than one code
rule,
.I cg
Explanation of this must wait for the description of the
file mach.c below.
.IP 5)
+The
+.I labeldef
+statement. Its only argument should be that of the
+.I lab
+pseudo-instruction. This is needed to generate local labels when the
+top element size information is used. It takes the form
+.DS
+ labeldef $i
+.DE
+.IP 6)
A temporary label of the form <digit>: may be placed here.
Expressions of the form [0-9][bf] in this code rule
generate the same string as is used for this label.
The stack pattern guarantees that everything will be stacked
before the jump is taken.
.DS
+pat lab topeltsize($1)==2 && !fallthrough($1)
+gen labeldef $1 yields r0
+
+pat lab topeltsize($1)==2 && fallthrough($1)
+with src2
+gen move %1,r0
+ labeldef $1 yields r0
+
+pat lab topeltsize($1)!=2
+with STACK
+kills all
+gen labeldef $1
+
+pat bra topeltsize($1)==2
+with src2 STACK
+ gen move %1,d0
+ jbr {label, $1}
+
+pat bra topeltsize($1)!=2
+with STACK
+ gen jbr {label, $1}
+.DE
+The combination of these patterns make sure that the top of the EM-stack will
+be in register r0 whenever necessary. The top element size mechanism will
+also show a size of 0 whenever a conditional branch to a label
+occurs. This saves a lot of patterns and hardly decreases performance.
+When the same register is used to return function results, this can save
+many moves to and from the stack.
+.DS
.ta 7.5c
pat cal
with STACK
Returns from this level of codegen().
Is used at the end of coercions,
move rules etc..
+.NH 4
+DO_LABDEF
+.PP
+This prints a label when the top element size mechanism is used. Only done on
+toplevel.
.NH 3
compute.c
.PP
pseudo associated.
There are functions to enter a symbol and to find a symbol.
.NH 3
+label.c
+.PP
+This module contains routines to handle the top element size messages.
+.NH 3
main.c
.PP
Main routine of the code generator.
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