On Tue, Jun 14, 2022 at 12:49 PM Eric Botcazou <botca...@adacore.com> wrote: > > > Hmm, I think instead of special-casing UNKNOWN_LOCATION > > what gimple_set_location should probably do is either not copy > > warnings at all or union them. Btw, gimple_set_location also > > removes a previously set BLOCK (but gimple_set_block preserves > > the location locus and diagnostic override). > > > > So I'd be tempted to axe the copy_warning () completely here. > > The first thing I tried, but it regressed the original testcase IIRC. > > Even my minimal patch manages to break bootstrap on ARM: > > buildslave/workspace/tcwg_gnu_1/abe/snapshots/gcc.git~master/libcpp/lex.cc: > 1523:9: error: pointer used after ‘void operator delete(void*, std::size_t)’ > [-Werror=use-after-free] > # 00:31:04 make[3]: *** [Makefile:227: lex.o] Error 1 > # 00:31:04 make[2]: *** [Makefile:9527: all-stage3-libcpp] Error 2 > # 00:31:35 make[1]: *** [Makefile:25887: stage3-bubble] Error 2 > # 00:31:35 make: *** [Makefile:1072: all] Error 2 > > /* Don't warn for cases like when a cdtor returns 'this' on ARM. */ > else if (warning_suppressed_p (var, OPT_Wuse_after_free)) > return; > > because warning-control.cc:copy_warning also clobbers the warning data of the > destination. We have in cp/decl.cc:maybe_return_this the lines: > > /* Return the address of the object. */ > tree val = DECL_ARGUMENTS (current_function_decl); > suppress_warning (val, OPT_Wuse_after_free); > > -Wuse-after-free is suppressed for the location of VAL and the TREE_NO_WARNING > bit set on it. But other expressions may have the same location as VAL and > the TREE_NO_WARNING bit _not_ set, so when you call copy_warning (expr, expr) > (we do that a lot after failed folding) for them, copy_warning erases the > warning data of the location. > > I have installed the obvious fixlet after testing on x86-64/Linux, but the > decoupling between TREE_NO_WARNING bit and location looks a bit problematic.
Thanks - that makes more sense. > > * warning-control.cc (copy_warning) [generic version]: Do not erase > the warning data of the destination location when the no-warning > bit is not set on the source. > (copy_warning) [tree version]: Return early if TO is equal to FROM. > (copy_warning) [gimple version]: Likewise. > testsuite/ > * g++.dg/warn/Wuse-after-free5.C: New test. > > -- > Eric Botcazou
