[Bug c/80756] missing diagnostic on non-constant expression with function call such as fabs or fma in initializer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80756 Andrew Pinski changed: What|Removed |Added Resolution|--- |INVALID Status|UNCONFIRMED |RESOLVED --- Comment #7 from Andrew Pinski --- As mentioned -std=c99 -pedantic-errors errors out like expected.
[Bug c/80756] missing diagnostic on non-constant expression with function call such as fabs or fma in initializer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80756 --- Comment #6 from joseph at codesourcery dot com --- On Mon, 15 May 2017, nsz at gcc dot gnu.org wrote: > fabs and fma identifiers are reserved for the implementation and it is valid > to > treat them as constant expression in initializers based on c99 6.6p10 The calls violate the requirement for constant expressions not to contain function calls, hence the pedwarns-if-pedantic being necessary for this code.
[Bug c/80756] missing diagnostic on non-constant expression with function call such as fabs or fma in initializer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80756 --- Comment #5 from joseph at codesourcery dot com --- On Mon, 15 May 2017, vincent-gcc at vinc17 dot net wrote: > GCC misses a diagnostic when the fabs() or fma() function is used in an > initializer. For instance, consider: There are pedwarns-if-pedantic for these cases. > Note that is not included, so that fabs() and fma() must not be > regarded as special. But even when these functions are regarded as ISO C's > specified ones, the diagnostic should probably still be present (it seems that > the C standard does not make an exception for such functions, unfortunately). The reservations with external linkage in C99/C11 7.1.3#1 are not conditional on whether the corresponding header is included. (Only C90 Amendment 1 had such reservations conditional on inclusion of the corresponding header, for the new functions it added, and that condition would only be relevant with -std=iso9899:199409.)
[Bug c/80756] missing diagnostic on non-constant expression with function call such as fabs or fma in initializer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80756 --- Comment #4 from Vincent Lefèvre --- (In reply to nsz from comment #3) > fabs and fma identifiers are reserved for the implementation and it is valid > to treat them as constant expression in initializers based on c99 6.6p10 Well, if is included, perhaps, but this would need to be documented as an implementation-defined behavior. The GCC manual Section 4 "C Implementation-Defined Behavior" doesn't seem to document such constant expressions and when they are available. If is not included, there should be at least a warning because fabs() or fma() is used without including the header first, thus potentially yielding unexpected results and obscure bugs.
[Bug c/80756] missing diagnostic on non-constant expression with function call such as fabs or fma in initializer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80756 nsz at gcc dot gnu.org changed: What|Removed |Added CC||nsz at gcc dot gnu.org --- Comment #3 from nsz at gcc dot gnu.org --- fabs and fma identifiers are reserved for the implementation and it is valid to treat them as constant expression in initializers based on c99 6.6p10 i think the gcc behaviour is reasonable.
[Bug c/80756] missing diagnostic on non-constant expression with function call such as fabs or fma in initializer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80756 --- Comment #2 from Vincent Lefèvre --- (In reply to Vincent Lefèvre from comment #1) > The cause seems to be that the functions are builtins: > > $ gcc-snapshot -std=c99 -c tst-cst.c [...] Oops, incomplete copy-paste. It should have been: $ gcc-snapshot -std=c99 -c tst-cst.c -fno-builtin tst-cst.c: In function 'f': tst-cst.c:7:21: error: initializer element is not constant static double x = fabs (3.0); ^~~~ tst-cst.c:8:21: error: initializer element is not constant static double y = fma (2.0, 3.0, 4.0); ^~~ tst-cst.c:9:21: error: initializer element is not constant static double z = foo (2.0, 3.0, 4.0); ^~~ Without the -fno-builtin, the diagnostic for fabs() and fma() are missing.
[Bug c/80756] missing diagnostic on non-constant expression with function call such as fabs or fma in initializer
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80756 --- Comment #1 from Vincent Lefèvre --- The cause seems to be that the functions are builtins: $ gcc-snapshot -std=c99 -c tst-cst.c tst-cst.c: In function 'f': tst-cst.c:7:21: error: initializer element is not constant static double x = fabs (3.0); ^~~~ tst-cst.c:8:21: error: initializer element is not constant static double y = fma (2.0, 3.0, 4.0); ^~~ tst-cst.c:9:21: error: initializer element is not constant static double z = foo (2.0, 3.0, 4.0); ^~~ But I think that this is wrong. The use of -std=c99 shouldn't allow builtin functions when they would give a different result (and even without -std=c99, as this would be confusing). On this point, Clang has the same issue.
