Message ID | 20211022172849.499625-1-pc@us.ibm.com |
---|---|
State | New |
Headers | show |
Series | rs6000: Add optimizations for _mm_sad_epu8 | expand |
Gentle ping... On Fri, Oct 22, 2021 at 12:28:49PM -0500, Paul A. Clarke via Gcc-patches wrote: > Power9 ISA added `vabsdub` instruction which is realized in the > `vec_absd` instrinsic. > > Use `vec_absd` for `_mm_sad_epu8` compatibility intrinsic, when > `_ARCH_PWR9`. > > Also, the realization of `vec_sum2s` on little-endian includes > two shifts in order to position the input and output to match > the semantics of `vec_sum2s`: > - Shift the second input vector left 12 bytes. In the current usage, > that vector is `{0}`, so this shift is unnecessary, but is currently > not eliminated under optimization. > - Shift the vector produced by the `vsum2sws` instruction left 4 bytes. > The two words within each doubleword of this (shifted) result must then > be explicitly swapped to match the semantics of `_mm_sad_epu8`, > effectively reversing this shift. So, this shift (and a susequent swap) > are unnecessary, but not currently removed under optimization. > > Using `__builtin_altivec_vsum2sws` retains both shifts, so is not an > option for removing the shifts. > > For little-endian, use the `vsum2sws` instruction directly, and > eliminate the explicit shift (swap). > > 2021-10-22 Paul A. Clarke <pc@us.ibm.com> > > gcc > * config/rs6000/emmintrin.h (_mm_sad_epu8): Use vec_absd > when _ARCH_PWR9, optimize vec_sum2s when LE. > --- > Tested on powerpc64le-linux on Power9, with and without `-mcpu=power9`, > and on powerpc/powerpc64-linux on Power8. > > OK for trunk? > > gcc/config/rs6000/emmintrin.h | 24 +++++++++++++++++------- > 1 file changed, 17 insertions(+), 7 deletions(-) > > diff --git a/gcc/config/rs6000/emmintrin.h b/gcc/config/rs6000/emmintrin.h > index ab16c13c379e..c4758be0e777 100644 > --- a/gcc/config/rs6000/emmintrin.h > +++ b/gcc/config/rs6000/emmintrin.h > @@ -2197,27 +2197,37 @@ extern __inline __m128i __attribute__((__gnu_inline__, __always_inline__, __arti > _mm_sad_epu8 (__m128i __A, __m128i __B) > { > __v16qu a, b; > - __v16qu vmin, vmax, vabsdiff; > + __v16qu vabsdiff; > __v4si vsum; > const __v4su zero = { 0, 0, 0, 0 }; > __v4si result; > > a = (__v16qu) __A; > b = (__v16qu) __B; > - vmin = vec_min (a, b); > - vmax = vec_max (a, b); > +#ifndef _ARCH_PWR9 > + __v16qu vmin = vec_min (a, b); > + __v16qu vmax = vec_max (a, b); > vabsdiff = vec_sub (vmax, vmin); > +#else > + vabsdiff = vec_absd (a, b); > +#endif > /* Sum four groups of bytes into integers. */ > vsum = (__vector signed int) vec_sum4s (vabsdiff, zero); > +#ifdef __LITTLE_ENDIAN__ > + /* Sum across four integers with two integer results. */ > + asm ("vsum2sws %0,%1,%2" : "=v" (result) : "v" (vsum), "v" (zero)); > + /* Note: vec_sum2s could be used here, but on little-endian, vector > + shifts are added that are not needed for this use-case. > + A vector shift to correctly position the 32-bit integer results > + (currently at [0] and [2]) to [1] and [3] would then need to be > + swapped back again since the desired results are two 64-bit > + integers ([1]|[0] and [3]|[2]). Thus, no shift is performed. */ > +#else > /* Sum across four integers with two integer results. */ > result = vec_sum2s (vsum, (__vector signed int) zero); > /* Rotate the sums into the correct position. */ > -#ifdef __LITTLE_ENDIAN__ > - result = vec_sld (result, result, 4); > -#else > result = vec_sld (result, result, 6); > #endif > - /* Rotate the sums into the correct position. */ > return (__m128i) result; > } > > -- > 2.27.0 >
On Mon, Nov 08, 2021 at 11:43:26AM -0600, Paul A. Clarke via Gcc-patches wrote: > Gentle ping... Gentle re-ping. > On Fri, Oct 22, 2021 at 12:28:49PM -0500, Paul A. Clarke via Gcc-patches wrote: > > Power9 ISA added `vabsdub` instruction which is realized in the > > `vec_absd` instrinsic. > > > > Use `vec_absd` for `_mm_sad_epu8` compatibility intrinsic, when > > `_ARCH_PWR9`. > > > > Also, the realization of `vec_sum2s` on little-endian includes > > two shifts in order to position the input and output to match > > the semantics of `vec_sum2s`: > > - Shift the second input vector left 12 bytes. In the current usage, > > that vector is `{0}`, so this shift is unnecessary, but is currently > > not eliminated under optimization. > > - Shift the vector produced by the `vsum2sws` instruction left 4 bytes. > > The two words within each doubleword of this (shifted) result must then > > be explicitly swapped to match the semantics of `_mm_sad_epu8`, > > effectively reversing this shift. So, this shift (and a susequent swap) > > are unnecessary, but not currently removed under optimization. > > > > Using `__builtin_altivec_vsum2sws` retains both shifts, so is not an > > option for removing the shifts. > > > > For little-endian, use the `vsum2sws` instruction directly, and > > eliminate the explicit shift (swap). > > > > 2021-10-22 Paul A. Clarke <pc@us.ibm.com> > > > > gcc > > * config/rs6000/emmintrin.h (_mm_sad_epu8): Use vec_absd > > when _ARCH_PWR9, optimize vec_sum2s when LE. > > --- > > Tested on powerpc64le-linux on Power9, with and without `-mcpu=power9`, > > and on powerpc/powerpc64-linux on Power8. > > > > OK for trunk? > > > > gcc/config/rs6000/emmintrin.h | 24 +++++++++++++++++------- > > 1 file changed, 17 insertions(+), 7 deletions(-) > > > > diff --git a/gcc/config/rs6000/emmintrin.h b/gcc/config/rs6000/emmintrin.h > > index ab16c13c379e..c4758be0e777 100644 > > --- a/gcc/config/rs6000/emmintrin.h > > +++ b/gcc/config/rs6000/emmintrin.h > > @@ -2197,27 +2197,37 @@ extern __inline __m128i __attribute__((__gnu_inline__, __always_inline__, __arti > > _mm_sad_epu8 (__m128i __A, __m128i __B) > > { > > __v16qu a, b; > > - __v16qu vmin, vmax, vabsdiff; > > + __v16qu vabsdiff; > > __v4si vsum; > > const __v4su zero = { 0, 0, 0, 0 }; > > __v4si result; > > > > a = (__v16qu) __A; > > b = (__v16qu) __B; > > - vmin = vec_min (a, b); > > - vmax = vec_max (a, b); > > +#ifndef _ARCH_PWR9 > > + __v16qu vmin = vec_min (a, b); > > + __v16qu vmax = vec_max (a, b); > > vabsdiff = vec_sub (vmax, vmin); > > +#else > > + vabsdiff = vec_absd (a, b); > > +#endif > > /* Sum four groups of bytes into integers. */ > > vsum = (__vector signed int) vec_sum4s (vabsdiff, zero); > > +#ifdef __LITTLE_ENDIAN__ > > + /* Sum across four integers with two integer results. */ > > + asm ("vsum2sws %0,%1,%2" : "=v" (result) : "v" (vsum), "v" (zero)); > > + /* Note: vec_sum2s could be used here, but on little-endian, vector > > + shifts are added that are not needed for this use-case. > > + A vector shift to correctly position the 32-bit integer results > > + (currently at [0] and [2]) to [1] and [3] would then need to be > > + swapped back again since the desired results are two 64-bit > > + integers ([1]|[0] and [3]|[2]). Thus, no shift is performed. */ > > +#else > > /* Sum across four integers with two integer results. */ > > result = vec_sum2s (vsum, (__vector signed int) zero); > > /* Rotate the sums into the correct position. */ > > -#ifdef __LITTLE_ENDIAN__ > > - result = vec_sld (result, result, 4); > > -#else > > result = vec_sld (result, result, 6); > > #endif > > - /* Rotate the sums into the correct position. */ > > return (__m128i) result; > > } > > > > -- > > 2.27.0 > >
Hi! On Fri, Oct 22, 2021 at 12:28:49PM -0500, Paul A. Clarke wrote: > Power9 ISA added `vabsdub` instruction which is realized in the > `vec_absd` instrinsic. > > Use `vec_absd` for `_mm_sad_epu8` compatibility intrinsic, when > `_ARCH_PWR9`. > > Also, the realization of `vec_sum2s` on little-endian includes > two shifts in order to position the input and output to match > the semantics of `vec_sum2s`: > - Shift the second input vector left 12 bytes. In the current usage, > that vector is `{0}`, so this shift is unnecessary, but is currently > not eliminated under optimization. The vsum2sws implementation uses an unspec, so there is almost no chance of anything with it being optimised :-( It rotates it right by 4 bytes btw, it's not a shift. > - Shift the vector produced by the `vsum2sws` instruction left 4 bytes. > The two words within each doubleword of this (shifted) result must then > be explicitly swapped to match the semantics of `_mm_sad_epu8`, > effectively reversing this shift. So, this shift (and a susequent swap) > are unnecessary, but not currently removed under optimization. Rotate left by 4 -- same thing once you consider word 0 and 2 are set to zeroes by the sum2sws. Not sure why it is not optimised, what do the dump files say? -dap and I'd start looking at the combine dump. > Using `__builtin_altivec_vsum2sws` retains both shifts, so is not an > option for removing the shifts. > > For little-endian, use the `vsum2sws` instruction directly, and > eliminate the explicit shift (swap). > > 2021-10-22 Paul A. Clarke <pc@us.ibm.com> > > gcc > * config/rs6000/emmintrin.h (_mm_sad_epu8): Use vec_absd > when _ARCH_PWR9, optimize vec_sum2s when LE. Please don't break changelog lines early. > - vmin = vec_min (a, b); > - vmax = vec_max (a, b); > +#ifndef _ARCH_PWR9 > + __v16qu vmin = vec_min (a, b); > + __v16qu vmax = vec_max (a, b); > vabsdiff = vec_sub (vmax, vmin); > +#else > + vabsdiff = vec_absd (a, b); > +#endif So hrm, maybe we should have the vec_absd macro (or the builtin) always, just expanding to three insns if necessary. Okay for trunk with approproate changelog and commit message changes. Thanks! Segher
diff --git a/gcc/config/rs6000/emmintrin.h b/gcc/config/rs6000/emmintrin.h index ab16c13c379e..c4758be0e777 100644 --- a/gcc/config/rs6000/emmintrin.h +++ b/gcc/config/rs6000/emmintrin.h @@ -2197,27 +2197,37 @@ extern __inline __m128i __attribute__((__gnu_inline__, __always_inline__, __arti _mm_sad_epu8 (__m128i __A, __m128i __B) { __v16qu a, b; - __v16qu vmin, vmax, vabsdiff; + __v16qu vabsdiff; __v4si vsum; const __v4su zero = { 0, 0, 0, 0 }; __v4si result; a = (__v16qu) __A; b = (__v16qu) __B; - vmin = vec_min (a, b); - vmax = vec_max (a, b); +#ifndef _ARCH_PWR9 + __v16qu vmin = vec_min (a, b); + __v16qu vmax = vec_max (a, b); vabsdiff = vec_sub (vmax, vmin); +#else + vabsdiff = vec_absd (a, b); +#endif /* Sum four groups of bytes into integers. */ vsum = (__vector signed int) vec_sum4s (vabsdiff, zero); +#ifdef __LITTLE_ENDIAN__ + /* Sum across four integers with two integer results. */ + asm ("vsum2sws %0,%1,%2" : "=v" (result) : "v" (vsum), "v" (zero)); + /* Note: vec_sum2s could be used here, but on little-endian, vector + shifts are added that are not needed for this use-case. + A vector shift to correctly position the 32-bit integer results + (currently at [0] and [2]) to [1] and [3] would then need to be + swapped back again since the desired results are two 64-bit + integers ([1]|[0] and [3]|[2]). Thus, no shift is performed. */ +#else /* Sum across four integers with two integer results. */ result = vec_sum2s (vsum, (__vector signed int) zero); /* Rotate the sums into the correct position. */ -#ifdef __LITTLE_ENDIAN__ - result = vec_sld (result, result, 4); -#else result = vec_sld (result, result, 6); #endif - /* Rotate the sums into the correct position. */ return (__m128i) result; }