| Message ID | 20230830015808.19870-4-yangyujie@loongson.cn |
|---|---|
| State | New |
| Headers | show |
| Series | LoongArch: target configuration interface update | expand |
On Wed, 2023-08-30 at 09:58 +0800, Yang Yujie wrote: > LoongArch processors may not support memory accesses without natural > alignments. Building libraries with -mstrict-align may help with > toolchain binary compatiblity and performance on these implementations > (e.g. Loongson 2K1000LA). > > No significant performance degredation is observed on current mainstream > LoongArch processors when the option is enabled. > > gcc/ChangeLog: > > * config.gcc: use -mstrict-align for building libraries > if --with-strict-align-lib is given. Isn't this equivalent to --with-default-multilib=mno-strict-align now? And I still believe the easiest way for 2K1000LA is adding -march=la264 support so the user can simply configure with --with-arch=la264. > --- > gcc/config.gcc | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > diff --git a/gcc/config.gcc b/gcc/config.gcc > index 4fae672a3b7..ed70fa63268 100644 > --- a/gcc/config.gcc > +++ b/gcc/config.gcc > @@ -4892,7 +4892,7 @@ case "${target}" in > ;; > > loongarch*-*) > - supported_defaults="abi arch tune fpu simd multilib- > default" > + supported_defaults="abi arch tune fpu simd multilib- > default strict-align-lib" > > # Local variables > unset \ > @@ -5089,6 +5089,17 @@ case "${target}" in > ;; > esac > > + # Build libraries with -mstrict-align if --with- > strict-align-lib is given. > + case ${with_strict_align_lib} in > + yes) strict_align_opt="/mstrict-align" ;; > + ""|no) ;; > + *) > + echo "Unknown option: --with-strict-align- > lib=${with_strict_align_lib}" 1>&2 > + exit 1 > + ;; > + esac > + > + > # Handle --with-multilib-default > if echo "${with_multilib_default}" \ > | grep -E -e '[[:space:]]' -e '//' -e '/$' -e '^/' > > /dev/null 2>&1; then > @@ -5250,6 +5261,9 @@ case "${target}" in > ;; > esac > > + # Use mstrict-align for building libraries if > --with-strict-align-lib is given. > + loongarch_multilib_list_make="${loongarch_mult > ilib_list_make}${strict_align_opt}" > + > # Check for repeated configuration of the same > multilib variant. > if echo "${elem_abi_base}/${elem_abi_ext}" \ > | grep -E "^(${all_abis%|})$" >/dev/null > 2>&1; then
> > LoongArch processors may not support memory accesses without natural > > alignments. Building libraries with -mstrict-align may help with > > toolchain binary compatiblity and performance on these implementations > > (e.g. Loongson 2K1000LA). > > > > No significant performance degredation is observed on current mainstream > > LoongArch processors when the option is enabled. > > > > gcc/ChangeLog: > > > > * config.gcc: use -mstrict-align for building libraries > > if --with-strict-align-lib is given. > > Isn't this equivalent to --with-default-multilib=mno-strict-align now? > > And I still believe the easiest way for 2K1000LA is adding -march=la264 > support so the user can simply configure with --with-arch=la264. Not exactly -- Options given in --with-multilib-default= will not be applied to multilib variants that have build options specified in --with-multilib-list, but --with-strict-align-lib is always effective. e.g. for the following configuration: --with-multilib-default=mstrict-align --with-multilib-list=lp64d/la464,lp64s The library build options would be: base/lp64d variant: -mabi=lp64d -march=la464 (no -mstrict-align appended) base/lp64s variant: -mabi=lp64s -march=abi-default -mstrict-align Sure, you can do it with --with-arch=la264. It's just a convenient switch that we can use for building generic toolchains.
On Wed, 2023-08-30 at 14:51 +0800, Yujie Yang wrote: > > > LoongArch processors may not support memory accesses without natural > > > alignments. Building libraries with -mstrict-align may help with > > > toolchain binary compatiblity and performance on these implementations > > > (e.g. Loongson 2K1000LA). > > > > > > No significant performance degredation is observed on current mainstream > > > LoongArch processors when the option is enabled. > > > > > > gcc/ChangeLog: > > > > > > * config.gcc: use -mstrict-align for building libraries > > > if --with-strict-align-lib is given. > > > > Isn't this equivalent to --with-default-multilib=mno-strict-align now? > > > > And I still believe the easiest way for 2K1000LA is adding -march=la264 > > support so the user can simply configure with --with-arch=la264. > > Not exactly -- Options given in --with-multilib-default= will not be applied > to multilib variants that have build options specified in --with-multilib-list, > but --with-strict-align-lib is always effective. > > e.g. for the following configuration: > > --with-multilib-default=mstrict-align > --with-multilib-list=lp64d/la464,lp64s > > The library build options would be: > > base/lp64d variant: -mabi=lp64d -march=la464 (no -mstrict-align appended) > base/lp64s variant: -mabi=lp64s -march=abi-default -mstrict-align > > Sure, you can do it with --with-arch=la264. It's just a convenient > switch that we can use for building generic toolchains. If you want a generic toolchain, it should default to -mstrict-align as well. Or it will still do unexpected thing for cases like: struct foo { char x; int y; } __attribute__ ((packed)); int get (struct foo *foo) { return foo->y; } So it should be --with-strict-align (it should make the *compiler* default to -mstrict-align). But them it seems --with-arch=la264 is just easier... Or maybe we should add -march=la64-baseline (or another name?) as the "bottom line" of a LA64 CPU. Currently the definition of - march=loongarch64 includes unaligned access and 64-bit FP support, so IMO we should have a baseline definition if we need to support something "below" loongarch64.
On Wed, Aug 30, 2023 at 04:22:13PM +0800, Xi Ruoyao wrote: > On Wed, 2023-08-30 at 14:51 +0800, Yujie Yang wrote: > > > > LoongArch processors may not support memory accesses without natural > > > > alignments. Building libraries with -mstrict-align may help with > > > > toolchain binary compatiblity and performance on these implementations > > > > (e.g. Loongson 2K1000LA). > > > > > > > > No significant performance degredation is observed on current mainstream > > > > LoongArch processors when the option is enabled. > > > > > > > > gcc/ChangeLog: > > > > > > > > * config.gcc: use -mstrict-align for building libraries > > > > if --with-strict-align-lib is given. > > > > > > Isn't this equivalent to --with-default-multilib=mno-strict-align now? > > > > > > And I still believe the easiest way for 2K1000LA is adding -march=la264 > > > support so the user can simply configure with --with-arch=la264. > > > > Not exactly -- Options given in --with-multilib-default= will not be applied > > to multilib variants that have build options specified in --with-multilib-list, > > but --with-strict-align-lib is always effective. > > > > e.g. for the following configuration: > > > > --with-multilib-default=mstrict-align > > --with-multilib-list=lp64d/la464,lp64s > > > > The library build options would be: > > > > base/lp64d variant: -mabi=lp64d -march=la464 (no -mstrict-align appended) > > base/lp64s variant: -mabi=lp64s -march=abi-default -mstrict-align > > > > Sure, you can do it with --with-arch=la264. It's just a convenient > > switch that we can use for building generic toolchains. > > If you want a generic toolchain, it should default to -mstrict-align as > well. Or it will still do unexpected thing for cases like: > > struct foo { char x; int y; } __attribute__ ((packed)); > > int get (struct foo *foo) { return foo->y; } > > So it should be --with-strict-align (it should make the *compiler* > default to -mstrict-align). But them it seems --with-arch=la264 is just > easier... By "generic" I mean: when you enable "-march=la264"/"-march=la464" and link statically, you get a binary that's good for running on LA264/LA464 cores, respectively. It's more of a cross-toolchain case.
diff --git a/gcc/config.gcc b/gcc/config.gcc index 4fae672a3b7..ed70fa63268 100644 --- a/gcc/config.gcc +++ b/gcc/config.gcc @@ -4892,7 +4892,7 @@ case "${target}" in ;; loongarch*-*) - supported_defaults="abi arch tune fpu simd multilib-default" + supported_defaults="abi arch tune fpu simd multilib-default strict-align-lib" # Local variables unset \ @@ -5089,6 +5089,17 @@ case "${target}" in ;; esac + # Build libraries with -mstrict-align if --with-strict-align-lib is given. + case ${with_strict_align_lib} in + yes) strict_align_opt="/mstrict-align" ;; + ""|no) ;; + *) + echo "Unknown option: --with-strict-align-lib=${with_strict_align_lib}" 1>&2 + exit 1 + ;; + esac + + # Handle --with-multilib-default if echo "${with_multilib_default}" \ | grep -E -e '[[:space:]]' -e '//' -e '/$' -e '^/' > /dev/null 2>&1; then @@ -5250,6 +5261,9 @@ case "${target}" in ;; esac + # Use mstrict-align for building libraries if --with-strict-align-lib is given. + loongarch_multilib_list_make="${loongarch_multilib_list_make}${strict_align_opt}" + # Check for repeated configuration of the same multilib variant. if echo "${elem_abi_base}/${elem_abi_ext}" \ | grep -E "^(${all_abis%|})$" >/dev/null 2>&1; then