How can this Makefile be made better/easier/less redundant?

Question

I would like some advice about the following Makefile. It works fine, but it is overly redundant and not harnessing any most of the magic make can do to help a C project.

Its purpose is to test a small ANSI C library. Portability is important.

.PHONY : test

OPTIMIZE = -g
INCLUDE  = -I.
CC       = gcc
WARNINGS = -Wall -ansi -pedantic -Wno-long-long -Wextra -Wdeclaration-after-statement -Wendif-labels -Wconversion
CFLAGS   = $(WARNINGS) $(OPTIMIZE) $(INCLUDE)
COMPILE  = $(CC) $(CFLAGS)
LINK     = $(COMPILE)

all : time64.o bin/check_max

bin/check_max : time64.o time64_config.h bin/check_max.c
    $(LINK) time64.o bin/check_max.c -o $@

time64.o : time64_config.h time64.h time64.c Makefile

t/bench : t/bench.c time64.o
    $(LINK) time64.o t/bench.c -o $@

bench : t/bench
    time t/bench

t/localtime_test : t/localtime_test.c time64.o
    $(LINK) time64.o t/localtime_test.c -o $@

t/gmtime_test : t/gmtime_test.c time64.o
    $(LINK) time64.o t/gmtime_test.c -o $@

t/year_limit.t : t/tap.c t/year_limit.t.c time64.o
    $(LINK) time64.o t/year_limit.t.c -o $@

t/negative.t : t/tap.c t/negative.t.c time64.o
    $(LINK) time64.o t/negative.t.c -o $@

t/overflow.t : t/tap.c t/overflow.t.c time64.o
    $(LINK) time64.o t/overflow.t.c -o $@

t/timegm.t : t/tap.c t/timegm.t.c time64.o
    $(LINK) time64.o t/timegm.t.c -o $@

t/safe_year.t : t/tap.c t/safe_year.t.c time64.c
    $(LINK) t/safe_year.t.c -o $@

t/gmtime64.t : t/tap.c t/gmtime64.t.c time64.o
    $(LINK) time64.o t/gmtime64.t.c -o $@

t/mktime64.t : t/tap.c t/mktime64.t.c time64.o
    $(LINK) time64.o t/mktime64.t.c -o $@

t/asctime64.t : t/tap.c t/asctime64.t.c time64.o
    $(LINK) time64.o t/asctime64.t.c -o $@

t/ctime64.t : t/tap.c t/ctime64.t.c time64.o
    $(LINK) time64.o t/ctime64.t.c -o $@

t/seconds_between_years.t : t/tap.c t/seconds_between_years.t.c time64.c
    $(LINK) t/seconds_between_years.t.c -o $@

test : tap_tests localtime_tests

localtime_tests: t/localtime_test t/gmtime_test
    @which bzdiff > /dev/null || (echo 'You need bzdiff to run these tests'; exit 1)
    @which less   > /dev/null || (echo 'You need less to run these tests';   exit 1)
    @echo "On failure, these tests will produce a diff between the failed and expected results.  If they pass they'll be quiet."
    TZ=Canada/Eastern t/gmtime_test | bzip2 -9 > t/gmtime_test.out.bz2
    bzdiff -u t/gmtime_test.out.bz2 t/gmtime.out.bz2 | less -F
    TZ=Canada/Eastern t/localtime_test | bzip2 -9 > t/eastern_test.out.bz2
    bzdiff -u t/eastern_test.out.bz2 t/eastern.out.bz2 | less -F
    TZ=Australia/West t/localtime_test | bzip2 -9 > t/oz_test.out.bz2
    bzdiff -u t/oz_test.out.bz2 t/oztime.out.bz2 | less -F

tap_tests: t/year_limit.t t/negative.t t/overflow.t t/timegm.t t/safe_year.t t/gmtime64.t t/asctime64.t t/ctime64.t
    @which prove > /dev/null || (echo 'You need prove (from the Test::Harness perl module) to run these tests'; exit 1)
    @prove --exec '' t/*.t

clean:
    -rm     t/*.t           \
        t/localtime_test    \
        t/gmtime_test       \
        t/*_test.out.bz2    \
        t/bench         \
        *.o

You can see it in situ here.

Answer 1

Use implicit rules and don't redeclare things make can find out automatically. Also simplified the variables at the top, but that's more preference (several merely reset default values). This is possibly slightly less portable, but not significantly so, IMHO. it's also more portable in some ways, e.g. on systems where 'gcc' isn't the default compiler.

Making localtime_tests and tap_tests into shell scripts (but not changing what they do), moves that logic elsewhere and is the main thing that makes the makefile readable daily.

CFLAGS = -g -Wall -ansi -pedantic -Wno-long-long -Wextra \
-Wdeclaration-after-statement -Wendif-labels -Wconversion

all : bin/check_max

bin/check_max : time64.o time64_config.h 
time64.o : time64_config.h time64.h Makefile

bench : t/bench
    time t/bench

t/bench : t/bench.c time64.o
t/localtime_test : time64.o
t/gmtime_test : time64.o

t/year_limit.t: t/tap.c time64.o
t/negative.t  : t/tap.c time64.o
t/overflow.t  : t/tap.c time64.o
t/timegm.t    : t/tap.c time64.o
t/safe_year.t : t/tap.c time64.c
t/gmtime64.t  : t/tap.c time64.o
t/mktime64.t  : t/tap.c time64.o
t/asctime64.t : t/tap.c time64.o
t/ctime64.t   : t/tap.c time64.o
t/seconds_between_years.t: t/tap.c time64.c

test : tap_tests localtime_tests
tap_tests: t/year_limit.t t/negative.t t/overflow.t t/timegm.t t/safe_year.t \
t/gmtime64.t t/asctime64.t t/ctime64.t
    ./tap_tests
localtime_tests: t/localtime_test t/gmtime_test
    ./localtime_tests
.PHONY : test tap_tests localtime_tests

clean:
    -rm t/*.t t/localtime_test t/gmtime_test t/*_test.out.bz2 t/bench
    -rm *.o
.PHONY : clean

You can make use of GNUmake-specific features to simplify even more, if that loss of portability is acceptable.