https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68641
Bug ID: 68641
Summary: undefined variables implicitly considered to be zero
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: Joost.VandeVondele at mat dot ethz.ch
Target Milestone: ---
This is an enhancement request. Using -O1 and higher, undefined variables are
considered equal to 0 in optimization. This leads to code compiling at -O1 but
failing to compile at -O0, for example :
> cat test.f90
INTEGER :: i
INTEGER, POINTER :: foo
IF (i/=0) CALL link_error
IF (ASSOCIATED(foo)) CALL link_error
END
another disadvantage is that e.g. using valgrind, the above program will not
fail when compiled at -O1. Only at -O0 these cases will be found (leading to
much longer testing times).
Using -Wmaybe-uninitialized is not a real solution, there are just too many
false positives (I'm not aware of a -Wmust-be-uninitialized, which would be
valuable).
So, ideally no optimization is done based on an assumed value.
