notes

把pascal程序转成C语言程序 把pascal程序转成C语言程序

   Support the "BigSetConst" option by creating constant arrays just as the
   Pascal compiler does.

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   The 2^(N+1) - 2^M method for generating [M..N] is not safe if N is 31.
   If the small-sets we are dealing with encompass the value 31 (== setbits-1)
   then we must use the bitwise construction instead.  (Currently, the
   translator just issues a note.)

   (If N is 31, 2^32 will most likely evaluate to 0 on most machines, which
   is the correct value.  So this is only a minor problem.)

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   Big-set constants right now are always folded.  Provide a mechanism
   for defined set constants, say by having a #define with an argument
   which is the name of the temporary variable to use for the set.

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   Should we convert NA_LONGWORD-type variants into C casts?

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   Are there implementations of strcpy that do not return their first
   argument?  If so, should have an option that says so.

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   Handle absolute-addressed variables better.  For  var a[12345]:integer,
   create an initialized int *.  For  var a['foo']:integer, create an int *
   which is initialized to NULL and accessed by a macro which locates the
   symbol the first time the variable is used.

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   Handle the idiom, "reset(f, name); open(f);"

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   Should have an option that lowercases all file names used in "reset",
   "fixfname", etc.  This should be on by default.

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   Add more complete support for conformant arrays.  Specifically, support
   non-GNU compilers by converting variable-sized array declarations into
   pointer declarations with calls to alloca or malloc/free (what if the
   function uses free and contains return statements)?  Also convert
   variable-array references into explicit index arithmetic.

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   Have a mode in which the body of a TRY-RECOVER is moved out into
   a sub-procedure all its own, communicating with the parent through
   varstructs as usual, so that the ANSI C warning about what longjmp
   can do to the local variables is avoided.  Alternatively, have an
   option in which all necessary locals are declared volatile when
   setjmps are present.

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   If a sub-procedure refers to a parent's variable with the VAX Pascal
   [STATIC] attribute, that variable is declared "static" inside the
   varstruct!  Need to convert it into a varref to a static variable in
   the parent.

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   When comparing records and arrays a la UCSD Pascal, should expand
   into an "&&" expression comparing each field individually.  (What about
   variants?  Maybe just compare the first variant, or the tagged
   variant.)  Probably best to write a struct-comparison function the
   first time a given type of struct is compared; that way, the function
   can include a complete if tree or switch statement in the case of
   tagged unions.

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   In the checkvarchanged code, take aliasing of VAR parameters into account.
   For example, in "procedure p(s1 : string; var s2 : string)" p2c now avoids
   copying s1 if s1 is not changed within p, but probably should also require
   that s2 not change, or at least that s1 have been read and used before s2
   is changed.

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   Provide an option that tells the code generator to provide helpful
   comments of its own when generated code may be obscure.


=============================================================================


   Compact the various data structures.  In particular, typical runs
   show the majority of memory is used by Meanings and Symbols for
   global and imported objects.

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   The program wastes memory.  Find ways to reduce memory usage, and to
   avoid leaving dead records on the heap.  (Garbage collection?  Yuck!)
   (Maybe GC between each function declaration would be okay.)

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   Assign better names to temporaries.  Also, could avoid making redundant
   temporaries by generating a unique temporary every time one is needed,
   then crunching them down at the end just before the declarations are
   written out.  Each temporary would maintain a list of all the other
   temporaries (of the same type) with which it would conflict.  (This
   would avoid the current method's waste when several temps are created,
   then most are cancelled.)  Also, note that char STR1[10], STR2[20] can
   be considered type-compatible and merged into STR[20].

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   Don't generate _STR_xxx structure names if they aren't forward-referenced.

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   Can optimize, e.g., "strpos(a,b) = 0" to a call to strstr() or strchr(),
   even though these ANSI functions are not Pascal-like enough to use in 
   the general case.

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   Complete the handling of "usecommas=0" mode.

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   Optimize "s := strltrim(s)", "s := strrtrim(s)", and both together.

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   Convert "(ch < 'a') or (ch > 'z')" to "!islower(ch)", and so on.
   Also do "!islower(ch) && !isupper(ch)" => "!isalpha(ch)", etc.

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   Find other cases in which to call mixassignments().

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   The sequence:   sprintf(buf + strlen(buf), "...", ...);
                   sprintf(buf + strlen(buf), "...", ...);
   could be changed to a single sprintf.
   Also, "sprintf(temp, "...%s", ..., buf); strcpy(buf, temp); (above);"
   could be crunched down.  (This comes from strinsert, then strappend.)

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   If there is only one assignment to a structured function's return
   variable, and that assignment is at the very end and assigns a local
   variable to the return variable, then merge the variables.
   (Example: name_list in netcmp's datastruct module.  RET_name_list
   should be renamed to namestr.)

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   Have an option that causes if-then-else's to be replaced by ? :'s in
   certain cases.  If the branches of the if are either both returns or
   both assignments to the same variable, which has no side effects, and
   if the whole conditional will be simple enough to fit on one line when
   printed, then the ? : transformation is okay.

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   Have an option that finds cases of multiple assignment.  For example:
      a := x; b := x;   =>  a = b = x;
      a := x; b := a;   =>  a = b = x;
   (provided the objects in question have the same type).

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   Need an option that causes $if$'s to change to #if's, instead of being
   evaluated at translation-time.  (This is *really hard* in general;
   do it for some common cases, such as entire statements being commented
   out, or fields being commented out of records.)

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   Have an option that prevents generation and inclusion of .h files for
   modules; instead, each module would contain extern declarations for
   the things it imports.  (Only declare names that are actually used---
   this means the declarations will have to be emitted on a procedure-by-
   procedure basis.)

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   Extend the ExpandIncludes option to compile include files as separate
   stand-alone C modules.  The hard part is warning when the new module
   uses a procedure which was declared static in an earlier C module.
   Remember to re-emit all the proper #include's at the beginning.
   Anything else?

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   Consider an option where the variables in a varStruct are made into
   globals instead, or into parameters if there are few of them.

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   Get flow analysis to eliminate redundant nil pointer checks.
   Also, there's still room for improvement in the handling of
   file names in StructFiles mode.

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   Need a method for simple pattern matching predicates in FuncMacros.
   For example, allow special translations of functions where a given
   argument is a known constant, or known to be positive, or two
   arguments are the same, etc.

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   Have some way to provide run-time templates for fixblock/fixexpr-like
   applications.  The user enters two C expressions A and B, possibly including
   Prolog-like logical variables.  If fixexpr sees an expression matching A,
   it rewrites it into the form of B.

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   Have an option to cause selected Pascal procedures or functions to be
   expanded in-line.  Do this either by generating the keyword "inline",
   or by doing the expansion in the translator.

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   Technically speaking, strcmp shouldn't be used to compute < and > for
   strings on a machine with signed chars.  Should we care?

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   Have an option for creating a "display" of LINK pointers local to a
   function.  Should only create such pointers for static levels which are
   referred to in the function body.

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