Re: [bootstrap-O3] add a default initializer to avoid a warning at -O3
On Wed, 2017-01-04 at 09:04 -0700, Jeff Law wrote: > On 01/04/2017 06:42 AM, Jason Merrill wrote: > > On Wed, Jan 4, 2017 at 8:13 AM, Alexandre Oliva > > wrote: > > > On Jan 3, 2017, Jason Merrill wrote: > > > > > > > Are there bugzillas for these false positive warnings? > > > > > > I don't think so. > > > > > > Did you mean in the sense that the patch silences them and thus > > > "fixes" > > > them, or in the sense that the underlying cause for the warnings > > > is not > > > fixed and someone might want to look into them at a later time? > > > > > > FWIW, I hadn't considered the latter (it doesn't seem too hard to > > > find > > > such warnings anyway; every time I try bootstrap-O3, which is not > > > very > > > often, I get a few of those), and the former didn't seem enough > > > of a > > > reason to have bug reports created. > > > > The latter; false positive warnings like this are bugs that should > > be fixed. > For the -O1 stuff the lower optimization level disables the > optimizers > that would identify and optimize away the infeasible path. > > For -O3 cases with unrolling, the unroller can create oob array > references with a guard. Our ability to exploit the guard isn't as > strong as it should be -- we've got BZs for this already. > > For the -O3 these are cases where the inliner exposes the infeasible > path, but we're not currently able to analyze the infeasible path. > > One could argue that any initializer we add ought to avoid a false > positive for -O2 or -O3 ought to be marked and a bug opened. But I > didn't feel it was worth pushing for that level of rigor since at > most > these are missed optimizations. But it would certainly be nice. FWIW I've filed PR middle-end/78993 about the input.c false positive that Alex's patch addresses; I *think* it's a case where the inliner has exposed an infeasible path (but I could be wrong).
Re: [bootstrap-O3] add a default initializer to avoid a warning at -O3
On 01/04/2017 06:42 AM, Jason Merrill wrote: On Wed, Jan 4, 2017 at 8:13 AM, Alexandre Oliva wrote: On Jan 3, 2017, Jason Merrill wrote: Are there bugzillas for these false positive warnings? I don't think so. Did you mean in the sense that the patch silences them and thus "fixes" them, or in the sense that the underlying cause for the warnings is not fixed and someone might want to look into them at a later time? FWIW, I hadn't considered the latter (it doesn't seem too hard to find such warnings anyway; every time I try bootstrap-O3, which is not very often, I get a few of those), and the former didn't seem enough of a reason to have bug reports created. The latter; false positive warnings like this are bugs that should be fixed. For the -O1 stuff the lower optimization level disables the optimizers that would identify and optimize away the infeasible path. For -O3 cases with unrolling, the unroller can create oob array references with a guard. Our ability to exploit the guard isn't as strong as it should be -- we've got BZs for this already. For the -O3 these are cases where the inliner exposes the infeasible path, but we're not currently able to analyze the infeasible path. One could argue that any initializer we add ought to avoid a false positive for -O2 or -O3 ought to be marked and a bug opened. But I didn't feel it was worth pushing for that level of rigor since at most these are missed optimizations. But it would certainly be nice. jeff
Re: [bootstrap-O3] add a default initializer to avoid a warning at -O3
On Wed, Jan 4, 2017 at 8:13 AM, Alexandre Oliva wrote: > On Jan 3, 2017, Jason Merrill wrote: > >> Are there bugzillas for these false positive warnings? > > I don't think so. > > Did you mean in the sense that the patch silences them and thus "fixes" > them, or in the sense that the underlying cause for the warnings is not > fixed and someone might want to look into them at a later time? > > FWIW, I hadn't considered the latter (it doesn't seem too hard to find > such warnings anyway; every time I try bootstrap-O3, which is not very > often, I get a few of those), and the former didn't seem enough of a > reason to have bug reports created. The latter; false positive warnings like this are bugs that should be fixed. Jason
Re: [bootstrap-O3] add a default initializer to avoid a warning at -O3
On Jan 3, 2017, Jason Merrill wrote: > Are there bugzillas for these false positive warnings? I don't think so. Did you mean in the sense that the patch silences them and thus "fixes" them, or in the sense that the underlying cause for the warnings is not fixed and someone might want to look into them at a later time? FWIW, I hadn't considered the latter (it doesn't seem too hard to find such warnings anyway; every time I try bootstrap-O3, which is not very often, I get a few of those), and the former didn't seem enough of a reason to have bug reports created. -- Alexandre Oliva, freedom fighterhttp://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
Re: [bootstrap-O3] add a default initializer to avoid a warning at -O3
Are there bugzillas for these false positive warnings? On Tue, Jan 3, 2017 at 12:45 PM, Jeff Law wrote: > On 01/02/2017 10:28 PM, Alexandre Oliva wrote: >> >> Building with the bootstrap-O3 configuration option fails to compile >> input.c due to an AFAICT false-positive warning about an uninitialized >> use of a variable. >> >> This patch adds a default initializer to silence it. >> >> Regstrapped on x86_64-linux-gnu and i686-linux-gnu. OK to install? >> >> for gcc/ChangeLog >> >> * input.c (assert_char_at_range): Default-initialize >> actual_range. > > OK. > jeff >
Re: [bootstrap-O3] add a default initializer to avoid a warning at -O3
On 01/02/2017 10:28 PM, Alexandre Oliva wrote: Building with the bootstrap-O3 configuration option fails to compile input.c due to an AFAICT false-positive warning about an uninitialized use of a variable. This patch adds a default initializer to silence it. Regstrapped on x86_64-linux-gnu and i686-linux-gnu. OK to install? for gcc/ChangeLog * input.c (assert_char_at_range): Default-initialize actual_range. OK. jeff
[bootstrap-O3] add a default initializer to avoid a warning at -O3
Building with the bootstrap-O3 configuration option fails to compile input.c due to an AFAICT false-positive warning about an uninitialized use of a variable. This patch adds a default initializer to silence it. Regstrapped on x86_64-linux-gnu and i686-linux-gnu. OK to install? for gcc/ChangeLog * input.c (assert_char_at_range): Default-initialize actual_range. --- gcc/input.c |2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/gcc/input.c b/gcc/input.c index dcb5101..a478873 100644 --- a/gcc/input.c +++ b/gcc/input.c @@ -2168,7 +2168,7 @@ assert_char_at_range (const location &loc, cpp_reader *pfile = test.m_parser; string_concat_db *concats = &test.m_concats; - source_range actual_range; + source_range actual_range = source_range(); const char *err = get_source_range_for_char (pfile, concats, strloc, type, idx, &actual_range); -- Alexandre Oliva, freedom fighterhttp://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
