On 9/30/20 6:14 PM, Martin Sebor via Gcc-patches wrote: > -Wstring-compare triggers under the same strict conditions as > the strcmp/strncmp call is folded into a constant: only when > all the uses of the result are [in]equality expressions with > zero. However, even when the call cannot be folded into > a constant because the result is in addition used in other > expressions besides equality to zero, GCC still sets the range > of the result to nonzero. So in more complex functions where > some of the uses of the same result are in tests for equality > to zero and others in other expressions, the warning fails to > point out the very mistake it's designed to detect. > > The attached change enhances the function that determines how > the strcmp/strncmp is used to also make it possible to detect > the mistakes in the multi-use situations. > > Tested on x86_64-linux & by building Glibc and Binutils/GDB > and confirming it triggers no new warnings. > > Martin > > gcc-95673.diff > > PR middle-end/95673 - missing -Wstring-compare for an impossible strncmp test > > gcc/ChangeLog: > > PR middle-end/95673 > * tree-ssa-strlen.c (used_only_for_zero_equality): Rename... > (use_in_zero_equality): ...to this. Add a default argument. > (handle_builtin_memcmp): Adjust to the name change above. > (handle_builtin_string_cmp): Same. > (maybe_warn_pointless_strcmp): Same. Pass in an explicit argument. > > gcc/testsuite/ChangeLog: > > PR middle-end/95673 > * gcc.dg/Wstring-compare-3.c: New test.
Please retest on the trunk and if testing is OK this is fine for the trunk. jeff
