PR 30735
PR 31090
* doc/invoke.texi: Document --params max-aliased-vops and
avg-aliased-vops.
* tree-ssa-operands.h (get_mpt_for, dump_memory_partitions,
debug_memory_partitions): Move to tree-flow.h
* params.h (AVG_ALIASED_VOPS): Define.
* tree-ssa-alias.c (struct mp_info_def): Remove. Update all
users.
(mp_info_t): Likewise.
(get_mem_sym_stats_for): New.
(set_memory_partition): Move from tree-flow-inline.h.
(mark_non_addressable): Only clear the set of symbols for the
partition if it exists.
(dump_memory_partitions): Move from tree-ssa-operands.c
(debug_memory_partitions): Likewise.
(need_to_partition_p): New.
(dump_mem_ref_stats): New.
(debug_mem_ref_stats): New.
(dump_mem_sym_stats): New.
(debug_mem_sym_stats): New.
(update_mem_sym_stats_from_stmt): New.
(compare_mp_info_entries): New.
(mp_info_cmp): Call it.
(sort_mp_info): Change argument to a list of mem_sym_stats_t
objects.
(get_mpt_for): Move from tree-ssa-operands.c.
(find_partition_for): New.
(create_partition_for): Remove.
(estimate_vop_reduction): New.
(update_reference_counts): New.
(build_mp_info): New.
(compute_memory_partitions): Refactor.
Document new heuristic.
Call build_mp_info, update_reference_counts,
find_partition_for and estimate_vop_reduction.
(compute_may_aliases): Populate virtual operands before
calling debugging dumps.
(delete_mem_sym_stats): New.
(delete_mem_ref_stats): New.
(init_mem_ref_stats): New.
(init_alias_info): Call it.
(maybe_create_global_var): Remove alias_info argument.
Get number of call sites and number of pure/const call sites
from gimple_mem_ref_stats().
(dump_alias_info): Call dump_memory_partitions first.
(dump_points_to_info_for): Show how many times a pointer has
been dereferenced.
* opts.c (decode_options): For -O2 set --param
max-aliased-vops to 500.
For -O3 set --param max-aliased-vops to 1000 and --param
avg-aliased-vops to 3.
* fortran/options.c (gfc_init_options): Remove assignment to
MAX_ALIASED_VOPS.
* tree-flow-inline.h (gimple_mem_ref_stats): New.
* tree-dfa.c (dump_variable): Dump memory reference
statistics.
Dump NO_ALIAS* settings.
(referenced_var_lookup): Tidy.
(mem_sym_stats): New.
* tree-ssa-copy.c (may_propagate_copy): Return true if DEST
and ORIG are different SSA names for a memory partition.
* tree-ssa.c (delete_tree_ssa): Call delete_mem_ref_stats.
* tree-flow.h (struct mem_sym_stats_d): Define.
(mem_sym_stats_t): Define.
(struct mem_ref_stats_d): Define.
(struct gimple_df): Add field mem_ref_stats.
(enum noalias_state): Define.
(struct var_ann_d): Add bitfield noalias_state.
(mem_sym_stats, delete_mem_ref_stats, dump_mem_ref_stats,
debug_mem_ref_stats, debug_memory_partitions,
debug_mem_sym_stats): Declare.
* tree-ssa-structalias.c (update_alias_info): Update call
sites, pure/const call sites and asm sites in structure
returned by gimple_mem_ref_stats.
Remove local variable IS_POTENTIAL_DEREF.
Increase NUM_DEREFS if the memory expression is a potential
dereference.
Call update_mem_sym_stats_from_stmt.
If the memory references memory, call
update_mem_sym_stats_from_stmt for all the direct memory
symbol references found.
(intra_create_variable_infos): Set noalias_state field for
pointer arguments according to the value of
flag_argument_noalias.
* tree-ssa-structalias.h (struct alias_info): Remove fields
num_calls_found and num_pure_const_calls_found.
(update_mem_sym_stats_from_stmt): Declare.
* params.def (PARAM_MAX_ALIASED_VOPS): Change description.
Set default value to 100.
(PARAM_AVG_ALIASED_VOPS): Define.
From-SVN: r123719
Copyright (C) 2000, 2003 Free Software Foundation, Inc.
This file is intended to contain a few notes about writing C code
within GCC so that it compiles without error on the full range of
compilers GCC needs to be able to compile on.
The problem is that many ISO-standard constructs are not accepted by
either old or buggy compilers, and we keep getting bitten by them.
This knowledge until know has been sparsely spread around, so I
thought I'd collect it in one useful place. Please add and correct
any problems as you come across them.
I'm going to start from a base of the ISO C90 standard, since that is
probably what most people code to naturally. Obviously using
constructs introduced after that is not a good idea.
For the complete coding style conventions used in GCC, please read
http://gcc.gnu.org/codingconventions.html
String literals
---------------
Irix6 "cc -n32" and OSF4 "cc" have problems with constant string
initializers with parens around it, e.g.
const char string[] = ("A string");
This is unfortunate since this is what the GNU gettext macro N_
produces. You need to find a different way to code it.
Some compilers like MSVC++ have fairly low limits on the maximum
length of a string literal; 509 is the lowest we've come across. You
may need to break up a long printf statement into many smaller ones.
Empty macro arguments
---------------------
ISO C (6.8.3 in the 1990 standard) specifies the following:
If (before argument substitution) any argument consists of no
preprocessing tokens, the behavior is undefined.
This was relaxed by ISO C99, but some older compilers emit an error,
so code like
#define foo(x, y) x y
foo (bar, )
needs to be coded in some other way.
free and realloc
----------------
Some implementations crash upon attempts to free or realloc the null
pointer. Thus if mem might be null, you need to write
if (mem)
free (mem);
Trigraphs
---------
You weren't going to use them anyway, but some otherwise ISO C
compliant compilers do not accept trigraphs.
Suffixes on Integer Constants
-----------------------------
You should never use a 'l' suffix on integer constants ('L' is fine),
since it can easily be confused with the number '1'.
Common Coding Pitfalls
======================
errno
-----
errno might be declared as a macro.
Implicit int
------------
In C, the 'int' keyword can often be omitted from type declarations.
For instance, you can write
unsigned variable;
as shorthand for
unsigned int variable;
There are several places where this can cause trouble. First, suppose
'variable' is a long; then you might think
(unsigned) variable
would convert it to unsigned long. It does not. It converts to
unsigned int. This mostly causes problems on 64-bit platforms, where
long and int are not the same size.
Second, if you write a function definition with no return type at
all:
operate (int a, int b)
{
...
}
that function is expected to return int, *not* void. GCC will warn
about this.
Implicit function declarations always have return type int. So if you
correct the above definition to
void
operate (int a, int b)
...
but operate() is called above its definition, you will get an error
about a "type mismatch with previous implicit declaration". The cure
is to prototype all functions at the top of the file, or in an
appropriate header.
Char vs unsigned char vs int
----------------------------
In C, unqualified 'char' may be either signed or unsigned; it is the
implementation's choice. When you are processing 7-bit ASCII, it does
not matter. But when your program must handle arbitrary binary data,
or fully 8-bit character sets, you have a problem. The most obvious
issue is if you have a look-up table indexed by characters.
For instance, the character '\341' in ISO Latin 1 is SMALL LETTER A
WITH ACUTE ACCENT. In the proper locale, isalpha('\341') will be
true. But if you read '\341' from a file and store it in a plain
char, isalpha(c) may look up character 225, or it may look up
character -31. And the ctype table has no entry at offset -31, so
your program will crash. (If you're lucky.)
It is wise to use unsigned char everywhere you possibly can. This
avoids all these problems. Unfortunately, the routines in <string.h>
take plain char arguments, so you have to remember to cast them back
and forth - or avoid the use of strxxx() functions, which is probably
a good idea anyway.
Another common mistake is to use either char or unsigned char to
receive the result of getc() or related stdio functions. They may
return EOF, which is outside the range of values representable by
char. If you use char, some legal character value may be confused
with EOF, such as '\377' (SMALL LETTER Y WITH UMLAUT, in Latin-1).
The correct choice is int.
A more subtle version of the same mistake might look like this:
unsigned char pushback[NPUSHBACK];
int pbidx;
#define unget(c) (assert(pbidx < NPUSHBACK), pushback[pbidx++] = (c))
#define get(c) (pbidx ? pushback[--pbidx] : getchar())
...
unget(EOF);
which will mysteriously turn a pushed-back EOF into a SMALL LETTER Y
WITH UMLAUT.
Other common pitfalls
---------------------
o Expecting 'plain' char to be either sign or unsigned extending.
o Shifting an item by a negative amount or by greater than or equal to
the number of bits in a type (expecting shifts by 32 to be sensible
has caused quite a number of bugs at least in the early days).
o Expecting ints shifted right to be sign extended.
o Modifying the same value twice within one sequence point.
o Host vs. target floating point representation, including emitting NaNs
and Infinities in a form that the assembler handles.
o qsort being an unstable sort function (unstable in the sense that
multiple items that sort the same may be sorted in different orders
by different qsort functions).
o Passing incorrect types to fprintf and friends.
o Adding a function declaration for a module declared in another file to
a .c file instead of to a .h file.