| Message ID | orsezmc6h3.fsf@lxoliva.fsfla.org |
|---|---|
| State | New |
| Headers | show |
| Series | [libstdc++,testsuite] disable SRA for compare_exchange_padding | expand |
On Tue, 16 Apr 2024 at 04:49, Alexandre Oliva <oliva@adacore.com> wrote: > > > On arm-vx7r2, the uses of as.load() as initializer get SRAed, so the > padding bits in the tests are not what we might expect from full-word > struct copies. Aha, I was wondering why this was failing on ARM! > I tried adding a function to perform bitwise copying, but even taking > the as.load() argument by const&, we'd still construct a temporary > with SRAed field-wise copying. Unable to find another way to ensure > we wouldn't get a temporary, I went for disabling SRA. > > Regstrapped on x86_64-linux-gnu. Also tested with gcc-13 on arm-, > aarch64-, x86- and x86_64-vxworks7r2. Ok to install? Yes, thanks. > > > for libstdc++-v3/ChangeLog > > * testsuite/29_atomics/atomic/compare_exchange_padding.cc: > Disable SRA. > --- > .../29_atomics/atomic/compare_exchange_padding.cc | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc > index 2f18d426e7f7e..a6081968ca869 100644 > --- a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc > +++ b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc > @@ -1,6 +1,7 @@ > // { dg-do run { target c++20 } } > // { dg-require-atomic-cmpxchg-word "" } > // { dg-add-options libatomic } > +// { dg-additional-options "-fno-tree-sra" } > > #include <atomic> > #include <cstring> > @@ -26,10 +27,10 @@ main () > s.s = 42; > > std::atomic<S> as{ s }; > - auto ts = as.load(); > + auto ts = as.load(); // SRA might prevent copying of padding bits here. > VERIFY( !compare_struct(s, ts) ); // padding cleared on construction > as.exchange(s); > - auto es = as.load(); > + auto es = as.load(); // SRA might prevent copying of padding bits here. > VERIFY( compare_struct(ts, es) ); // padding cleared on exchange > > S n; > > -- > Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ > Free Software Activist GNU Toolchain Engineer > More tolerance and less prejudice are key for inclusion and diversity > Excluding neuro-others for not behaving ""normal"" is *not* inclusive
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc index 2f18d426e7f7e..a6081968ca869 100644 --- a/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc +++ b/libstdc++-v3/testsuite/29_atomics/atomic/compare_exchange_padding.cc @@ -1,6 +1,7 @@ // { dg-do run { target c++20 } } // { dg-require-atomic-cmpxchg-word "" } // { dg-add-options libatomic } +// { dg-additional-options "-fno-tree-sra" } #include <atomic> #include <cstring> @@ -26,10 +27,10 @@ main () s.s = 42; std::atomic<S> as{ s }; - auto ts = as.load(); + auto ts = as.load(); // SRA might prevent copying of padding bits here. VERIFY( !compare_struct(s, ts) ); // padding cleared on construction as.exchange(s); - auto es = as.load(); + auto es = as.load(); // SRA might prevent copying of padding bits here. VERIFY( compare_struct(ts, es) ); // padding cleared on exchange S n;
On arm-vx7r2, the uses of as.load() as initializer get SRAed, so the padding bits in the tests are not what we might expect from full-word struct copies. I tried adding a function to perform bitwise copying, but even taking the as.load() argument by const&, we'd still construct a temporary with SRAed field-wise copying. Unable to find another way to ensure we wouldn't get a temporary, I went for disabling SRA. Regstrapped on x86_64-linux-gnu. Also tested with gcc-13 on arm-, aarch64-, x86- and x86_64-vxworks7r2. Ok to install? for libstdc++-v3/ChangeLog * testsuite/29_atomics/atomic/compare_exchange_padding.cc: Disable SRA. --- .../29_atomics/atomic/compare_exchange_padding.cc | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)