| Summary: | missing warning comparing array address to null | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Martin Sebor <msebor> |
| Component: | c | Assignee: | Martin Sebor <msebor> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | egallager |
| Priority: | P3 | Keywords: | diagnostic, patch |
| Version: | 12.0 | ||
| Target Milestone: | 12.0 | ||
| See Also: |
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33925 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102555 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102867 |
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| Host: | Target: | ||
| Build: | Known to work: | ||
| Known to fail: | 10.2.0, 11.2.0, 12.0, 4.5.3, 4.6.4, 4.9.4, 5.5.0, 6.4.0, 7.2.0, 8.3.0, 9.1.0 | Last reconfirmed: | 2021-08-30 00:00:00 |
The master branch has been updated by Martin Sebor <msebor@gcc.gnu.org>: https://gcc.gnu.org/g:4dc7ce6fb3917958d1a6036d8acf2953b9c1b868 commit r12-4059-g4dc7ce6fb3917958d1a6036d8acf2953b9c1b868 Author: Martin Sebor <msebor@redhat.com> Date: Fri Oct 1 11:50:25 2021 -0600 Enhance -Waddress to detect more suspicious expressions [PR102103]. Resolves: PR c/102103 - missing warning comparing array address to null gcc/ChangeLog: PR c/102103 * doc/invoke.texi (-Waddress): Update. * gengtype.c (write_types): Avoid -Waddress. * poly-int.h (POLY_SET_COEFF): Avoid using null. gcc/c-family/ChangeLog: PR c/102103 * c-common.c (decl_with_nonnull_addr_p): Handle members. Check and perform warning suppression. (c_common_truthvalue_conversion): Enhance warning suppression. gcc/c/ChangeLog: PR c/102103 * c-typeck.c (maybe_warn_for_null_address): New function. (build_binary_op): Call it. gcc/cp/ChangeLog: PR c/102103 * typeck.c (warn_for_null_address): Enhance. (cp_build_binary_op): Call it also for member pointers. gcc/fortran/ChangeLog: PR c/102103 * array.c: Remove an unnecessary test. * trans-array.c: Same. gcc/testsuite/ChangeLog: PR c/102103 * g++.dg/cpp0x/constexpr-array-ptr10.C: Suppress a valid warning. * g++.dg/warn/Wreturn-local-addr-6.C: Correct a cast. * gcc.dg/Waddress.c: Expect a warning. * c-c++-common/Waddress-3.c: New test. * c-c++-common/Waddress-4.c: New test. * g++.dg/warn/Waddress-5.C: New test. * g++.dg/warn/Waddress-6.C: New test. * g++.dg/warn/pr101219.C: Expect a warning. * gcc.dg/Waddress-3.c: New test. Done for GCC 12. This should probably get a note in gcc-12/changes.html IMO |
GCC issues -Waddress only for the equality test in f() but not those in g() or h(), even though all three evaluate to false (and even though GCC folds all three to false even with no optimization). It would be helpful to diagnose all three. $ cat z.c && gcc -S -Wall -fdump-tree-optimized=/dev/stdout z.c void f (void) { int i; if (&i == 0) // -Waddress (good) __builtin_abort (); } void g (void) { int a[1]; if (a == 0) // missing warning __builtin_abort (); } void h (void) { int a[1][2]; if (a[0] == 0) // missing warning __builtin_abort (); } z.c: In function ‘f’: z.c:4:10: warning: the comparison will always evaluate as ‘false’ for the address of ‘i’ will never be NULL [-Waddress] 4 | if (&i == 0) // -Waddress (good) | ^~ ;; Function f (f, funcdef_no=0, decl_uid=1943, cgraph_uid=1, symbol_order=0) void f () { int i; <bb 2> : i ={v} {CLOBBER}; return; } ;; Function g (g, funcdef_no=1, decl_uid=1947, cgraph_uid=2, symbol_order=1) void g () { int a[1]; <bb 2> : a ={v} {CLOBBER}; return; } ;; Function h (h, funcdef_no=2, decl_uid=1951, cgraph_uid=3, symbol_order=2) void h () { int a[1][2]; <bb 2> : a ={v} {CLOBBER}; return; } Clang diagnoses both the one in f() and in g() (but not the one in h()). GCC 4.4.7 does as well but the latter has been lost since GCC 4.5 (see https://gcc.godbolt.org/z/8dbjxv89E) so technically this could be viewed as a regression.