On Tue, 22 Mar 2016, Jakub Jelinek wrote:
> Hi!
>
> As the testcase shows, the C/C++ FEs narrow the shift counters from whatever
> type they had originally to unsigned int (previously signed int).
> Then the vect-patterns code, to be able to use vector by vector shifts
> attempts to narrow or widen them again to the right type. If there is
> already a cast from the right precision, it just uses the rhs1 of that case,
> otherwise it adds a cast to the pattern, which performs the needed widening
> or narrowing.
>
> Unfortunately, we have information loss during optimizations, we don't know
> anymore if it was say:
> long a[64], b[64];
> void foo (void)
> {
> for (int i = 0; i < 64; i++)
> a[i] <<= b[i]; // Here we don't need any masking, it would be UB
> // if b isn't in range
> }
> void bar (void)
> {
> for (int i = 0; i < 64; i++)
> a[i] <<= (unsigned) b[i]; // But here we can't just use b[i] as the
> // shift count, because the upper bits are to be
> masked off.
> }
True. I suppose as signed ops with well-defined overflow would come
in useful sometimes here we'd like to have a conversion with
undefined overflow behavior to capture this fact in the IL...
> void baz (void)
> {
> for (int i = 0; i < 64; i++)
> a[i] <<= b[i] - 0x7200000000ULL; // And here the optimizers will likely
> // optimize away the subtraction, because
> there
> // is implicit cast to (unsigned int). We
> need
> // to mask instead of using b[i] directly.
> }
> But, not casting say long long shift counters to unsigned int would penalize
> other code, computing unneeded operations. So I'm afraid we want the
> following fix, which I've bootstrapped/regtested on x86_64-linux and
> i686-linux. For short/char shifts we don't need this of course.
>
> Ok for trunk?
Ok.
Thanks,
Richard.
> 2016-03-22 Jakub Jelinek <[email protected]>
>
> PR tree-optimization/70354
> * tree-vect-patterns.c (vect_recog_vector_vector_shift_pattern): If
> oprnd0 is wider than oprnd1 and there is a cast from the wider
> type to oprnd1, mask it with the mask of the narrower type.
>
> * gcc.dg/vect/pr70354-1.c: New test.
> * gcc.dg/vect/pr70354-2.c: New test.
> * gcc.target/i386/avx2-pr70354-1.c: New test.
> * gcc.target/i386/avx2-pr70354-2.c: New test.
>
> --- gcc/tree-vect-patterns.c.jj 2016-03-04 15:42:12.000000000 +0100
> +++ gcc/tree-vect-patterns.c 2016-03-22 15:28:24.403579426 +0100
> @@ -2097,7 +2097,20 @@ vect_recog_vector_vector_shift_pattern (
> if (TYPE_MODE (TREE_TYPE (rhs1)) == TYPE_MODE (TREE_TYPE (oprnd0))
> && TYPE_PRECISION (TREE_TYPE (rhs1))
> == TYPE_PRECISION (TREE_TYPE (oprnd0)))
> - def = rhs1;
> + {
> + if (TYPE_PRECISION (TREE_TYPE (oprnd1))
> + >= TYPE_PRECISION (TREE_TYPE (rhs1)))
> + def = rhs1;
> + else
> + {
> + tree mask
> + = build_low_bits_mask (TREE_TYPE (rhs1),
> + TYPE_PRECISION (TREE_TYPE (oprnd1)));
> + def = vect_recog_temp_ssa_var (TREE_TYPE (rhs1), NULL);
> + def_stmt = gimple_build_assign (def, BIT_AND_EXPR, rhs1, mask);
> + new_pattern_def_seq (stmt_vinfo, def_stmt);
> + }
> + }
> }
>
> if (def == NULL_TREE)
> --- gcc/testsuite/gcc.dg/vect/pr70354-1.c.jj 2016-03-22 15:36:42.210847707
> +0100
> +++ gcc/testsuite/gcc.dg/vect/pr70354-1.c 2016-03-22 15:47:45.448878909
> +0100
> @@ -0,0 +1,50 @@
> +/* PR tree-optimization/70354 */
> +/* { dg-do run } */
> +
> +#ifndef main
> +#include "tree-vect.h"
> +#endif
> +
> +long long int b[64], c[64], g[64];
> +unsigned long long int a[64], d[64], e[64], f[64], h[64];
> +
> +__attribute__ ((noinline, noclone)) void
> +foo (void)
> +{
> + int i;
> + for (i = 0; i < 64; i++)
> + {
> + d[i] = h[i] << (((((unsigned long long int) b[i] * e[i])
> + << (-a[i] - 3752448776177690134ULL))
> + - 8214565720323784703ULL) - 1ULL);
> + e[i] = (_Bool) (f[i] + (unsigned long long int) g[i]);
> + g[i] = c[i];
> + }
> +}
> +
> +int
> +main ()
> +{
> + int i;
> +#ifndef main
> + check_vect ();
> +#endif
> + if (__CHAR_BIT__ != 8 || sizeof (long long int) != 8)
> + return 0;
> + for (i = 0; i < 64; ++i)
> + {
> + a[i] = 14694295297531861425ULL;
> + b[i] = -1725558902283030715LL;
> + c[i] = 4402992416302558097LL;
> + e[i] = 6297173129107286501ULL;
> + f[i] = 13865724171235650855ULL;
> + g[i] = 982871027473857427LL;
> + h[i] = 8193845517487445944ULL;
> + }
> + foo ();
> + for (i = 0; i < 64; i++)
> + if (d[i] != 8193845517487445944ULL || e[i] != 1
> + || g[i] != 4402992416302558097ULL)
> + abort ();
> + return 0;
> +}
> --- gcc/testsuite/gcc.dg/vect/pr70354-2.c.jj 2016-03-22 15:36:45.527802852
> +0100
> +++ gcc/testsuite/gcc.dg/vect/pr70354-2.c 2016-03-22 16:07:09.397164461
> +0100
> @@ -0,0 +1,37 @@
> +/* PR tree-optimization/70354 */
> +/* { dg-do run } */
> +
> +#ifndef main
> +#include "tree-vect.h"
> +#endif
> +
> +unsigned long long a[64], b[64];
> +
> +__attribute__((noinline, noclone)) void
> +foo (void)
> +{
> + int i;
> + for (i = 0; i < 64; i++)
> + a[i] <<= (b[i] - 0x1200000000ULL);
> +}
> +
> +int
> +main ()
> +{
> + int i;
> +#ifndef main
> + check_vect ();
> +#endif
> + if (__CHAR_BIT__ != 8 || sizeof (long long int) != 8)
> + return 0;
> + for (i = 0; i < 64; i++)
> + {
> + a[i] = 0x1234ULL;
> + b[i] = 0x1200000000ULL + (i % 54);
> + }
> + foo ();
> + for (i = 0; i < 64; i++)
> + if (a[i] != (0x1234ULL << (i % 54)))
> + abort ();
> + return 0;
> +}
> --- gcc/testsuite/gcc.target/i386/avx2-pr70354-1.c.jj 2016-03-22
> 15:44:42.228356553 +0100
> +++ gcc/testsuite/gcc.target/i386/avx2-pr70354-1.c 2016-03-22
> 15:47:26.738131930 +0100
> @@ -0,0 +1,16 @@
> +/* PR tree-optimization/70354 */
> +/* { dg-do run } */
> +/* { dg-options "-O2 -ftree-vectorize -mavx2" } */
> +/* { dg-require-effective-target avx2 } */
> +
> +#include "avx2-check.h"
> +
> +#define main() do_main ()
> +
> +#include "../../gcc.dg/vect/pr70354-1.c"
> +
> +static void
> +avx2_test (void)
> +{
> + do_main ();
> +}
> --- gcc/testsuite/gcc.target/i386/avx2-pr70354-2.c.jj 2016-03-22
> 15:44:50.283247629 +0100
> +++ gcc/testsuite/gcc.target/i386/avx2-pr70354-2.c 2016-03-22
> 15:44:55.856172268 +0100
> @@ -0,0 +1,16 @@
> +/* PR tree-optimization/70354 */
> +/* { dg-do run } */
> +/* { dg-options "-O2 -ftree-vectorize -mavx2" } */
> +/* { dg-require-effective-target avx2 } */
> +
> +#include "avx2-check.h"
> +
> +#define main() do_main ()
> +
> +#include "../../gcc.dg/vect/pr70354-2.c"
> +
> +static void
> +avx2_test (void)
> +{
> + do_main ();
> +}
>
> Jakub
>
>
--
Richard Biener <[email protected]>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
