Re: [PATCH 2/2] cprop_hardreg: Enable propagation of the stack pointer if possible.

[Philipp Tomsich <philipp.tomsich@vrull.eu>]

This should be covered by PR110308 (proposed fix attached there) and PR110313.
Our bootstrap runs are still in progress to confirm.


On Thu, 22 Jun 2023 at 09:40, Richard Biener <richard.guenther@gmail.com> wrote:
>
> On Thu, Jun 22, 2023 at 1:42 AM Thiago Jung Bauermann
> <thiago.bauermann@linaro.org> wrote:
> >
> >
> > Hello,
> >
> > Jeff Law <jeffreyalaw@gmail.com> writes:
> >
> > > On 6/19/23 22:52, Tamar Christina wrote:
> > >
> > >>> It's a bit hackish, but could we reject the stack pointer for operand1 in the
> > >>> stack-tie?  And if we do so, does it help?
> > >> Yeah this one I had to defer until later this week to look at closer because what I'm
> > >> wondering about is whether the optimization should apply to frame related
> > >> RTX as well.
> > >> Looking at the description of RTX_FRAME_RELATED_P that this optimization may
> > >> end up de-optimizing RISC targets by creating an offset that is larger than offset
> > >> which can be used from a SP making reload having to spill.  i.e. sometimes the
> > >> move was explicitly done. So perhaps it should not apply it to
> > >> RTX_FRAME_RELATED_P in find_oldest_value_reg and copyprop_hardreg_forward_1?
> > >> Other parts of this pass already seems to bail out in similar situations. So I needed
> > >> to
> > >> write some testcases to check what would happen in these cases hence the deferral.
> > >> to later in the week.
> > > Rejecting for RTX_FRAME_RELATED_P would seem reasonable and probably better in general to
> > > me.  The cases where we're looking to clean things up aren't really in the
> > > prologue/epilogue, but instead in the main body after register elimination has turned fp
> > > into sp + offset, thus making all kinds of things no longer valid.
> >
> > The problems I reported were fixed by commits:
> >
> > 580b74a79146 "aarch64: Robustify stack tie handling"
> > 079f31c55318 "aarch64: Fix gcc.target/aarch64/sve/pcs failures"
> >
> > Thanks!
> >
> > But unfortunately I'm still seeing bootstrap failures (ICE segmentation
> > fault) in today's trunk with build config bootstrap-lto in both
> > armv8l-linux-gnueabihf and aarch64-linux-gnu.
>
> If there's not yet a bugreport for this please make sure to open one so
> this issue doesn't get lost.
>
> > If I revert commit 6a2e8dcbbd4b "cprop_hardreg: Enable propagation of
> > the stack pointer if possible" from trunk then both bootstraps succeed.
> >
> > Here's the command I'm using to build on armv8l:
> >
> > ~/src/configure \
> >     SHELL=/bin/bash \
> >     --with-gnu-as \
> >     --with-gnu-ld \
> >     --disable-libmudflap \
> >     --enable-lto \
> >     --enable-shared \
> >     --without-included-gettext \
> >     --enable-nls \
> >     --with-system-zlib \
> >     --disable-sjlj-exceptions \
> >     --enable-gnu-unique-object \
> >     --enable-linker-build-id \
> >     --disable-libstdcxx-pch \
> >     --enable-c99 \
> >     --enable-clocale=gnu \
> >     --enable-libstdcxx-debug \
> >     --enable-long-long \
> >     --with-cloog=no \
> >     --with-ppl=no \
> >     --with-isl=no \
> >     --disable-multilib \
> >     --with-float=hard \
> >     --with-fpu=neon-fp-armv8 \
> >     --with-mode=thumb \
> >     --with-arch=armv8-a \
> >     --enable-threads=posix \
> >     --enable-multiarch \
> >     --enable-libstdcxx-time=yes \
> >     --enable-gnu-indirect-function \
> >     --disable-werror \
> >     --enable-checking=yes \
> >     --enable-bootstrap \
> >     --with-build-config=bootstrap-lto \
> >     --enable-languages=c,c++,fortran,lto \
> >     && make \
> >         profiledbootstrap \
> >         SHELL=/bin/bash \
> >         -w \
> >         -j 40 \
> >         CFLAGS_FOR_BUILD="-pipe -g -O2" \
> >         CXXFLAGS_FOR_BUILD="-pipe -g -O2" \
> >         LDFLAGS_FOR_BUILD="-static-libgcc" \
> >         MAKEINFOFLAGS=--force \
> >         BUILD_INFO="" \
> >         MAKEINFO=echo
> >
> > And here's the slightly different one for aarch64-linux:
> >
> > ~/src/configure \
> >     SHELL=/bin/bash \
> >     --with-gnu-as \
> >     --with-gnu-ld \
> >     --disable-libmudflap \
> >     --enable-lto \
> >     --enable-shared \
> >     --without-included-gettext \
> >     --enable-nls \
> >     --with-system-zlib \
> >     --disable-sjlj-exceptions \
> >     --enable-gnu-unique-object \
> >     --enable-linker-build-id \
> >     --disable-libstdcxx-pch \
> >     --enable-c99 \
> >     --enable-clocale=gnu \
> >     --enable-libstdcxx-debug \
> >     --enable-long-long \
> >     --with-cloog=no \
> >     --with-ppl=no \
> >     --with-isl=no \
> >     --disable-multilib \
> >     --enable-fix-cortex-a53-835769 \
> >     --enable-fix-cortex-a53-843419 \
> >     --with-arch=armv8-a \
> >     --enable-threads=posix \
> >     --enable-multiarch \
> >     --enable-libstdcxx-time=yes \
> >     --enable-gnu-indirect-function \
> >     --disable-werror \
> >     --enable-checking=yes \
> >     --enable-bootstrap \
> >     --with-build-config=bootstrap-lto \
> >     --enable-languages=c,c++,fortran,lto \
> >     && make \
> >         profiledbootstrap \
> >         SHELL=/bin/bash \
> >         -w \
> >         -j 40 \
> >         LDFLAGS_FOR_TARGET="-Wl,-fix-cortex-a53-843419" \
> >         CFLAGS_FOR_BUILD="-pipe -g -O2" \
> >         CXXFLAGS_FOR_BUILD="-pipe -g -O2" \
> >         LDFLAGS_FOR_BUILD="-static-libgcc" \
> >         MAKEINFOFLAGS=--force \
> >         BUILD_INFO="" \
> >         MAKEINFO=echo
> >
> > --
> > Thiago