gcc/gcc
Kenneth Zadeck 57512f5363 re PR middle-end/37448 (cannot compile big function)
2008-10-11  Kenneth Zadeck <zadeck@naturalbridge.com>

	PR rtl-optimization/37448
	* df.h: (df_ref_class): New enum.
	(DF_REF_TYPE_NAMES, df_ref_extract): Removed.
	(struct df_ref): Replaced with union df_ref_d.
	(df_base_ref, df_artificial_ref, df_regular_ref, df_extract_ref):
	New members of df_ref_d union.
	(DF_REF_REAL_REG, DF_REF_REGNO, DF_REF_REAL_LOC, DF_REF_REG,
	DF_REF_LOC, DF_REF_BB, DF_REF_INSN_INFO, DF_REF_INSN,
	DF_REF_CLASS, DF_REF_TYPE, DF_REF_CHAIN, DF_REF_ID, DF_REF_FLAGS,
	DF_REF_ORDER, DF_REF_IS_ARTIFICIAL, DF_REF_NEXT_REG,
	DF_REF_PREV_REG, DF_REF_EXTRACT_WIDTH, DF_REF_EXTRACT_OFFSET,
	DF_REF_EXTRACT_MODE): Replaced definition to access union
	df_ref_d.
       	(DF_MWS_REG_DEF_P, DF_MWS_REG_USE_P, DF_MWS_TYPE): New macros.
	(df_scan_bb_info, df_bb_regno_first_def_find,
	df_bb_regno_last_def_find, df_find_def, df_find_use,
	df_refs_chain_dump, df_regs_chain_dump, df_ref_debug,
	debug_df_ref, df_chain_create, df_chain_unlink, df_chain_copy,
	df_ref_create, df_ref_remove, df_compute_accessed_bytes,
	df_get_artificial_defs, df_get_artificial_uses, union_defs)
	Replaced struct df_ref * with df_ref.
	* df-scan.c (df_collection_rec, df_null_ref_rec,
	df_ref_chain_delete_du_chain, df_ref_chain_delete, df_install_ref,
	df_grow_ref_info, df_ref_create, df_reg_chain_unlink,
	df_ref_compress_rec, df_ref_remove, df_ref_chain_delete_du_chain,
	df_ref_chain_delete, df_free_collection_rec, df_insn_rescan,
	df_reorganize_refs_by_reg_by_reg,
	df_reorganize_refs_by_reg_by_insn, df_reorganize_refs_by_reg,
	df_ref_change_reg_with_loc_1, df_notes_rescan, df_swap_refs,
	df_sort_and_compress_refs, df_install_ref, df_install_refs,
	df_ref_record, df_get_conditional_uses, df_get_call_refs,
	df_bb_refs_record, df_exit_block_uses_collect,
	df_record_exit_block_uses, df_reg_chain_mark,
	df_reg_chain_verify_unmarked, df_refs_verify): Replaced struct
	df_ref * with df_ref.
	(df_ref_record, df_uses_record, df_ref_create_structure): Added
	df_ref_class parameter.
	(df_scan_problem_data): Added new pools for different types of
	refs.
	(df_scan_free_internal, df_scan_alloc, df_free_ref,
	df_ref_create_structure): Processed new ref pools.
	(df_scan_start_dump): Added counts of refs and insns.
	(df_ref_create, df_notes_rescan, df_def_record_1, df_uses_record,
	df_get_call_refs, df_insn_refs_collect, df_bb_refs_collect,
	df_entry_block_defs_collect, df_exit_block_uses_collect): Added
	code to pass df_ref_class down to ref creation functions.
	(df_reg_chain_unlink, df_ref_remove, df_ref_change_reg_with_loc_1,
	df_reg_chain_mark): Use macros to hide references to df_refs.
	(df_ref_chain_change_bb): Removed.
	(df_insn_change_bb): Remove calls to df_ref_insn_change_bb.
	(df_ref_equal_p, df_ref_compare, df_ref_create_structure):
	Enhanced to understand df_ref union structure.
	* fwprop.c (local_ref_killed_between_p, use_killed_between,
	all_uses_available_at, update_df, try_fwprop_subst,
	forward_propagate_subreg, forward_propagate_and_simplify,
	forward_propagate_into, fwprop, fwprop_addr): Replaced struct
	df_ref * with df_ref.
	(use_killed_between, all_uses_available_at): Use macros to hide
	references to df_refs.
	* regstat.c (regstat_bb_compute_ri,
	regstat_bb_compute_calls_crossed): Replaced struct df_ref * with
	df_ref.
	* see.c (see_handle_relevant_defs, see_handle_relevant_uses,
	see_handle_relevant_refs, see_analyze_one_def,
	see_update_relevancy, see_propagate_extensions_to_uses): Replaced
	struct df_ref * with df_ref.
	* ra-conflict.c (record_one_conflict, clear_reg_in_live,
	global_conflicts): Replaced struct df_ref * with df_ref.
	* ddg.c (create_ddg_dep_from_intra_loop_link,
	add_cross_iteration_register_deps, build_inter_loop_deps):
	Replaced struct df_ref * with df_ref.
	(create_ddg_dep_from_intra_loop_link,
	add_cross_iteration_register_deps): Use macros to hide references
	to df_refs.
	* auto-inc-dec.c (find_inc, merge_in_block): Replaced struct
	df_ref * with df_ref.
	* df-core.c (df_bb_regno_first_def_find,
	df_bb_regno_last_def_find, df_find_def, df_find_use,
	df_refs_chain_dump, df_regs_chain_dump, df_ref_debug,
	debug_df_ref): Replaced struct df_ref * with df_ref.
	(df_mws_dump, df_ref_debug): Use macros to hide references to
	df_refs.
	* cse.c (cse_extended_basic_block): Replaced struct df_ref * with
	df_ref.
	* web.c (union_defs, entry_register, replace_ref, web_main):
	Replaced struct df_ref * with df_ref.
	(union_defs, replace_ref): Use macros to hide references to
	df_refs.
	* global.c (compute_regs_asm_clobbered, build_insn_chain):
	Replaced struct df_ref * with df_ref.
	* ifcvt.c (dead_or_predicable): Replaced struct df_ref * with
	df_ref.
	* sel-sched-ir.c (maybe_downgrade_id_to_use, setup_id_reg_sets, ):
	Replaced struct df_ref * with df_ref.
	* ira-lives.c (mark_ref_live, def_conflicts_with_inputs_p,
	mark_ref_dead, process_bb_node_lives): Replaced struct df_ref *
	with df_ref.
	* local-alloc.c (block_alloc): Replaced struct df_ref * with
	df_ref.
	* df-byte-scan.c (df_compute_accessed_bytes_extract,
	df_compute_accessed_bytes_strict_low_part,
	df_compute_accessed_bytes_subreg, df_compute_accessed_bytes):
	Replaced struct df_ref * with df_ref.
	(df_compute_accessed_bytes): Use macros to hide references to
	df_refs.
	* init-regs.c (initialize_uninitialized_regs): Replaced struct
	df_ref * with df_ref.
	* loop-invariant.c (invariant_for_use, hash_invariant_expr_1,
	check_dependency, check_dependencies, record_uses): Replaced
	struct df_ref * with df_ref.
	(invariant_for_use, check_dependency): Use macros to hide
	references to df_refs.
	* loop-iv.c (iv_analysis_loop_init, iv_get_reaching_def,
	get_biv_step_1, get_biv_step, record_iv, iv_analyze_def,
	iv_analyze, biv_p): Replaced struct df_ref * with df_ref.
	(iv_analysis_loop_init, iv_get_reaching_def): Use macros to hide
	references to df_refs.
	* ira.c (compute_regs_asm_clobbered): Replaced struct df_ref * with df_ref.
	* combine.c (create_log_links): Replaced struct df_ref * with df_ref.
	* df-problems.c (df_rd_bb_local_compute_process_def,
	df_lr_bb_local_compute, df_live_bb_local_compute, df_chain_create,
	df_chain_unlink_1, df_chain_unlink, df_chain_copy,
	df_chain_remove_problem, df_chain_create_bb_process_use,
	df_chain_create_bb, df_chain_top_dump, df_chain_bottom_dump,
	df_byte_lr_check_regs, df_byte_lr_bb_local_compute,
	df_byte_lr_simulate_defs, df_byte_lr_simulate_uses,
	df_byte_lr_simulate_artificial_refs_at_top,
	df_byte_lr_simulate_artificial_refs_at_end, df_create_unused_note,
	df_note_bb_compute, df_note_add_problem, df_simulate_defs,
	df_simulate_uses, df_simulate_artificial_refs_at_end,
	df_simulate_artificial_refs_at_top): Replaced struct df_ref * with df_ref.
	(df_chain_dump): Use macros to hide
	references to df_refs.
	* config/mips/mips.c (r10k_simplify_address): Replaced struct
	df_ref * with df_ref.
	* dce.c (mark_nonreg_stores, delete_corresponding_reg_eq_notes,
	mark_artificial_uses, mark_reg_dependencies,
	byte_dce_process_block): Replaced struct df_ref * with df_ref.

From-SVN: r141067
2008-10-11 23:39:21 +00:00
..
ada
config re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
cp re PR c++/37146 (Invalid types with COND_EXPR) 2008-10-10 20:22:17 +02:00
doc rs6000.c (rs6000_parse_fpu_option): Interpret -mfpu options. 2008-10-11 09:33:04 -04:00
fortran re PR fortran/37794 (Fortran module overloading regression) 2008-10-11 12:09:23 +00:00
ginclude
java
objc
objcp
po
testsuite tree.h (contains_packed_reference): Mention ARRAY_RANGE_REF in head comment. 2008-10-11 19:48:47 +00:00
ABOUT-GCC-NLS
acinclude.m4
aclocal.m4
addresses.h
alias.c
alias.h
alloc-pool.c
alloc-pool.h
attribs.c
auto-inc-dec.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
BASE-VER
basic-block.h
bb-reorder.c
bitmap.c
bitmap.h
bt-load.c
builtin-attrs.def
builtin-types.def
builtins.c
builtins.def
c-aux-info.c
c-common.c
c-common.def
c-common.h
c-config-lang.in
c-convert.c
c-cppbuiltin.c
c-decl.c
c-dump.c
c-errors.c
c-format.c
c-format.h
c-gimplify.c c-gimplify.c (c_genericize): Don't refer to DECL_ASSEMBLER_NAME before ensuring it's already computed. 2008-10-10 07:20:30 +00:00
c-lang.c
c-lex.c
c-objc-common.c
c-objc-common.h
c-omp.c
c-opts.c
c-parser.c
c-pch.c
c-ppoutput.c
c-pragma.c
c-pragma.h
c-pretty-print.c
c-pretty-print.h
c-semantics.c
c-tree.h
c-typeck.c
c.opt
caller-save.c
calls.c
cfg.c
cfganal.c
cfgbuild.c
cfgcleanup.c
cfgexpand.c
cfghooks.c
cfghooks.h
cfglayout.c
cfglayout.h
cfgloop.c
cfgloop.h
cfgloopanal.c
cfgloopmanip.c
cfgrtl.c
cgraph.c
cgraph.h
cgraphbuild.c
cgraphunit.c
ChangeLog re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
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collect2.c
collect2.h
combine-stack-adj.c
combine.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
common.opt
conditions.h
config.build
config.gcc rs6000.c (rs6000_parse_fpu_option): Interpret -mfpu options. 2008-10-11 09:33:04 -04:00
config.host
config.in
configure
configure.ac
convert.c
convert.h
COPYING
COPYING3
COPYING3.LIB
COPYING.LIB
coretypes.h
coverage.c
coverage.h
cppdefault.c
cppdefault.h
cppspec.c
crtstuff.c
cse.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
cselib.c
cselib.h
cstamp-h.in
DATESTAMP Daily bump. 2008-10-11 00:18:40 +00:00
dbgcnt.c
dbgcnt.def
dbgcnt.h
dbxout.c
dbxout.h
dce.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
dce.h
ddg.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
ddg.h
debug.c
debug.h
defaults.h
DEV-PHASE
df-byte-scan.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
df-core.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
df-problems.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
df-scan.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
df.h re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
dfp.c
dfp.h
diagnostic.c
diagnostic.def
diagnostic.h
dojump.c
dominance.c
domwalk.c
domwalk.h
double-int.c
double-int.h
dse.c
dse.h
dummy-checksum.c
dwarf2.h
dwarf2asm.c
dwarf2asm.h
dwarf2out.c re PR debug/37002 (No debug info on unreferenced parameters after stack alignment) 2008-10-10 16:28:05 -07:00
dwarf2out.h
dwarf.h
ebitmap.c
ebitmap.h
emit-rtl.c
emit-rtl.h
emutls.c
errors.c
errors.h
et-forest.c
et-forest.h
except.c
except.h
exec-tool.in
explow.c
expmed.c
expr.c tree.h (contains_packed_reference): Mention ARRAY_RANGE_REF in head comment. 2008-10-11 19:48:47 +00:00
expr.h
final.c
fix-header.c
fixed-value.c
fixed-value.h
fixproto
flags.h
fold-const.c
fp-test.c
FSFChangeLog
FSFChangeLog.10
FSFChangeLog.11
function.c
function.h
fwprop.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
gbl-ctors.h
gcc.c
gcc.h
gccbug.in
gccspec.c
gcov-dump.c
gcov-io.c
gcov-io.h
gcov-iov.c
gcov.c
gcse.c
gdbinit.in
gen-protos.c
genattr.c
genattrtab.c
genautomata.c
gencheck.c
genchecksum.c
gencodes.c
genconditions.c
genconfig.c
genconstants.c
genemit.c
genextract.c
genflags.c
gengenrtl.c
gengtype-lex.l
gengtype-parse.c
gengtype.c
gengtype.h
genmddeps.c
genmodes.c
genmultilib
genopinit.c
genoutput.c
genpeep.c
genpreds.c
genrecog.c
gensupport.c
gensupport.h
ggc-common.c
ggc-none.c
ggc-page.c
ggc-zone.c
ggc.h
gimple-iterator.c
gimple-low.c
gimple-pretty-print.c
gimple.c
gimple.def
gimple.h
gimplify.c
glimits.h
global.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
graph.c
graph.h
graphds.c
graphds.h
graphite.c
graphite.h
gsstruct.def
gstab.h
gsyms.h
gsyslimits.h
gthr-aix.h
gthr-dce.h
gthr-gnat.c
gthr-gnat.h
gthr-lynx.h
gthr-mipssde.h
gthr-nks.h
gthr-posix95.h
gthr-posix.c
gthr-posix.h
gthr-rtems.h
gthr-single.h
gthr-solaris.h
gthr-tpf.h
gthr-vxworks.h
gthr-win32.h
gthr.h
haifa-sched.c
hard-reg-set.h
hooks.c
hooks.h
host-default.c
hosthooks-def.h
hosthooks.h
hwint.h
ifcvt.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
incpath.c
incpath.h
init-regs.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
input.h
insn-addr.h
insn-notes.def
integrate.c
integrate.h
intl.c
intl.h
ipa-cp.c
ipa-inline.c
ipa-prop.c
ipa-prop.h
ipa-pure-const.c
ipa-reference.c
ipa-reference.h
ipa-struct-reorg.c
ipa-struct-reorg.h
ipa-type-escape.c
ipa-type-escape.h
ipa-utils.c
ipa-utils.h
ipa.c
ira-build.c
ira-color.c
ira-conflicts.c
ira-costs.c
ira-emit.c
ira-int.h
ira-lives.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
ira.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
ira.h
jump.c
lambda-code.c
lambda-mat.c
lambda-trans.c
lambda.h
langhooks-def.h
langhooks.c
langhooks.h
LANGUAGES
lcm.c
libfuncs.h
libgcc2.c
libgcc2.h
libgcc-std.ver
libgcov.c
limitx.h
limity.h
lists.c
local-alloc.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
longlong.h
loop-doloop.c
loop-init.c
loop-invariant.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
loop-iv.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
loop-unroll.c
loop-unswitch.c
lower-subreg.c
machmode.def
machmode.h
main.c
Makefile.in
matrix-reorg.c
mcf.c
mips-tdump.c
mips-tfile.c
mkconfig.sh
mkmap-flat.awk
mkmap-symver.awk
mode-classes.def
mode-switching.c
modulo-sched.c
omega.c
omega.h
omp-builtins.def
omp-low.c
ONEWS
opt-functions.awk
opt-gather.awk
optabs.c
optabs.h
optc-gen.awk
opth-gen.awk
opts-common.c
opts.c
opts.h
output.h
params.c
params.def
params.h
passes.c
pointer-set.c
pointer-set.h
postreload-gcse.c
postreload.c
predict.c
predict.def
predict.h
prefix.c
prefix.h
pretty-print.c
pretty-print.h
print-rtl.c
print-tree.c
profile.c
profile.h
protoize.c
ra-conflict.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
ra.h
read-rtl.c
README.Portability
real.c
real.h
recog.c
recog.h
reg-notes.def
reg-stack.c
regclass.c
regmove.c
regrename.c
regs.h
regstat.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
reload1.c
reload.c
reload.h
reorg.c
resource.c
resource.h
rtl-error.c
rtl-factoring.c
rtl.c
rtl.def
rtl.h
rtlanal.c
rtlhooks-def.h
rtlhooks.c
sbitmap.c
sbitmap.h
scan-decls.c
scan-types.sh
scan.c
scan.h
sched-deps.c
sched-ebb.c
sched-int.h
sched-rgn.c
sched-vis.c
sdbout.c
sdbout.h
see.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
sel-sched-dump.c
sel-sched-dump.h
sel-sched-ir.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
sel-sched-ir.h
sel-sched.c
sel-sched.h
simplify-rtx.c
sort-protos
sparseset.c
sparseset.h
sreal.c
sreal.h
stab.def
stack-ptr-mod.c
statistics.c
statistics.h
stmt.c
stor-layout.c
stringpool.c
stub-objc.c
sync-builtins.def
sys-protos.h
sys-types.h
system.h
target-def.h
target.h
targhooks.c
targhooks.h
timevar.c
timevar.def
timevar.h
tlink.c
toplev.c
toplev.h
tracer.c
tree-affine.c
tree-affine.h
tree-browser.c
tree-browser.def
tree-call-cdce.c
tree-cfg.c
tree-cfgcleanup.c
tree-chrec.c
tree-chrec.h
tree-complex.c
tree-data-ref.c
tree-data-ref.h
tree-dfa.c
tree-dump.c
tree-dump.h
tree-eh.c
tree-flow-inline.h
tree-flow.h
tree-if-conv.c
tree-inline.c
tree-inline.h
tree-into-ssa.c
tree-iterator.c
tree-iterator.h
tree-loop-distribution.c
tree-loop-linear.c
tree-mudflap.c
tree-mudflap.h
tree-nested.c
tree-nomudflap.c
tree-nrv.c
tree-object-size.c
tree-optimize.c
tree-outof-ssa.c
tree-parloops.c
tree-pass.h
tree-phinodes.c
tree-predcom.c
tree-pretty-print.c
tree-profile.c
tree-scalar-evolution.c
tree-scalar-evolution.h
tree-sra.c
tree-ssa-address.c
tree-ssa-alias-warnings.c
tree-ssa-alias.c
tree-ssa-ccp.c
tree-ssa-coalesce.c
tree-ssa-copy.c
tree-ssa-copyrename.c
tree-ssa-dce.c
tree-ssa-dom.c
tree-ssa-dse.c
tree-ssa-forwprop.c
tree-ssa-ifcombine.c
tree-ssa-live.c
tree-ssa-live.h
tree-ssa-loop-ch.c
tree-ssa-loop-im.c
tree-ssa-loop-ivcanon.c
tree-ssa-loop-ivopts.c tree.h (contains_packed_reference): Mention ARRAY_RANGE_REF in head comment. 2008-10-11 19:48:47 +00:00
tree-ssa-loop-manip.c
tree-ssa-loop-niter.c
tree-ssa-loop-prefetch.c
tree-ssa-loop-unswitch.c
tree-ssa-loop.c
tree-ssa-math-opts.c
tree-ssa-operands.c
tree-ssa-operands.h
tree-ssa-phiopt.c
tree-ssa-phiprop.c
tree-ssa-pre.c
tree-ssa-propagate.c
tree-ssa-propagate.h
tree-ssa-reassoc.c
tree-ssa-sccvn.c
tree-ssa-sccvn.h
tree-ssa-sink.c
tree-ssa-structalias.c
tree-ssa-structalias.h
tree-ssa-ter.c
tree-ssa-threadedge.c
tree-ssa-threadupdate.c
tree-ssa-uncprop.c
tree-ssa.c
tree-ssanames.c
tree-stdarg.c
tree-stdarg.h
tree-switch-conversion.c re PR target/35760 (ICE with complex types and -static on PPC darwin) 2008-10-11 10:55:43 +02:00
tree-tailcall.c
tree-vect-analyze.c
tree-vect-generic.c
tree-vect-patterns.c
tree-vect-transform.c
tree-vectorizer.c
tree-vectorizer.h
tree-vrp.c
tree.c
tree.def
tree.h tree.h (contains_packed_reference): Mention ARRAY_RANGE_REF in head comment. 2008-10-11 19:48:47 +00:00
treestruct.def
tsystem.h
typeclass.h
unwind-c.c
unwind-compat.c
unwind-compat.h
unwind-dw2-fde-compat.c
unwind-dw2-fde-darwin.c
unwind-dw2-fde-glibc.c
unwind-dw2-fde.c
unwind-dw2-fde.h
unwind-dw2.c
unwind-dw2.h
unwind-generic.h
unwind-pe.h
unwind-sjlj.c
unwind.inc
value-prof.c
value-prof.h
var-tracking.c
varasm.c
varpool.c
varray.c
varray.h
vec.c
vec.h
vecprim.h
version.c
version.h
vmsdbg.h
vmsdbgout.c
web.c re PR middle-end/37448 (cannot compile big function) 2008-10-11 23:39:21 +00:00
xcoff.h
xcoffout.c
xcoffout.h

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.