https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69368
--- Comment #59 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> We already warn about mismatches sizes at LTO link time
Confirmed
[Book15] f90/bug% gfc -c -O2 pr69368_a.f90 -flto
[Book15] f90/bug% gfc -O2 pr69368_a.o pr69368_b.f90 -flto
pr69368_a.f90:3:0: warning: type of 'blk' does not match original declaration
[-Wlto-type-mismatch]
COMMON /BLK/ K(1)
pr69368_b.f90:3:0: note: 'blk' was previously declared here
COMMON /BLK/ K(64)
pr69368_b.f90:3:0: note: code may be misoptimized unless -fno-strict-aliasing
is used
and the executable gives the expected output. IMO the second note is bogus
(pr68717).
If I replace
COMMON /BLK/ K(1)
with
COMMON /BLK/ K(2)
the executable gives the expected output also for all the compiling options I
have tried.
AFAICT the code (invalid for any value of I and J)
FUNCTION FOO(I, J)
COMMON /BLK/ K(1)
FOO = K(I) + K(J) + K(2*I) + K(2*J)
END FUNCTION
is optimized as
FOO = K(I) + K(I) + K(I) + K(I)
Although I know that a compiler can do whatever it deems suitable with invalid
code, I don't understand the rationale of the above "optimization": it is as
invalid as the original code.
Another thing I don't understand is that the following code is not "optimized"
while as invalid as the one above:
INTEGER FUNCTION FOO(I, J, K)
INTEGER K(1)
FOO = K(I) + K(J) + K(2*I) + K(2*J)
END FUNCTION
INTEGER FOO
INTEGER K(64)
DO I=1,64
K(I)=I
END DO
IF (FOO(5,12,K).NE.51) CALL ABORT
END
