On Thu, 1 Jul 2021, Jiufu Guo wrote:
> For code like:
> unsigned foo(unsigned val, unsigned start)
> {
> unsigned cnt = 0;
> for (unsigned i = start; i > val; ++i)
> cnt++;
> return cnt;
> }
>
> The number of iterations should be about UINT_MAX - start.
For
unsigned foo(unsigned val, unsigned start)
{
unsigned cnt = 0;
for (unsigned i = start; i >= val; ++i)
cnt++;
return cnt;
}
and val == 0 the loop never terminates. I don't see anywhere
in the patch that you disregard GE_EXPR and I remember
the code handles GE as well as GT? From a quick look this is
also not covered by a testcase you add - not exactly sure
how it would materialize in a miscompilation.
> There is function adjust_cond_for_loop_until_wrap which
> handles similar work for const bases.
> Like adjust_cond_for_loop_until_wrap, this patch enhance
> function number_of_iterations_cond/number_of_iterations_lt
> to analyze number of iterations for this kind of loop.
>
> Bootstrap and regtest pass on powerpc64le, is this ok for trunk?
>
> gcc/ChangeLog:
>
> PR tree-optimization/101145
> * tree-ssa-loop-niter.c
> (number_of_iterations_until_wrap): New function.
> (number_of_iterations_lt): Invoke above function.
> (adjust_cond_for_loop_until_wrap):
> Merge to number_of_iterations_until_wrap.
> (number_of_iterations_cond): Update invokes for
> adjust_cond_for_loop_until_wrap and number_of_iterations_lt.
>
> gcc/testsuite/ChangeLog:
>
> PR tree-optimization/101145
> * gcc.dg/vect/pr101145.c: New test.
> * gcc.dg/vect/pr101145.inc: New test.
> * gcc.dg/vect/pr101145_1.c: New test.
> * gcc.dg/vect/pr101145_2.c: New test.
> * gcc.dg/vect/pr101145_3.c: New test.
> ---
> gcc/testsuite/gcc.dg/vect/pr101145.c | 187 +++++++++++++++++++++++++
> gcc/testsuite/gcc.dg/vect/pr101145.inc | 63 +++++++++
> gcc/testsuite/gcc.dg/vect/pr101145_1.c | 15 ++
> gcc/testsuite/gcc.dg/vect/pr101145_2.c | 15 ++
> gcc/testsuite/gcc.dg/vect/pr101145_3.c | 15 ++
> gcc/tree-ssa-loop-niter.c | 150 +++++++++++---------
> 6 files changed, 380 insertions(+), 65 deletions(-)
> create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145.c
> create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145.inc
> create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145_1.c
> create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145_2.c
> create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145_3.c
>
> diff --git a/gcc/testsuite/gcc.dg/vect/pr101145.c
> b/gcc/testsuite/gcc.dg/vect/pr101145.c
> new file mode 100644
> index 00000000000..74031b031cf
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145.c
> @@ -0,0 +1,187 @@
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-options "-O3 -fdump-tree-vect-details" } */
> +#include <limits.h>
> +
> +unsigned __attribute__ ((noinline))
> +foo (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
> +{
> + while (n < ++l)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +foo_1 (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned)
> +{
> + while (UINT_MAX - 64 < ++l)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +foo_2 (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
> +{
> + l = UINT_MAX - 32;
> + while (n < ++l)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +foo_3 (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
> +{
> + while (n <= ++l)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +foo_4 (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
> +{ // infininate
> + while (0 <= ++l)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +foo_5 (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
> +{
> + //no loop
> + l = UINT_MAX;
> + while (n < ++l)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +bar (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
> +{
> + while (--l < n)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +bar_1 (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned)
> +{
> + while (--l < 64)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +unsigned __attribute__ ((noinline))
> +bar_2 (int *__restrict__ a, int *__restrict__ b, unsigned l, unsigned n)
> +{
> + l = 32;
> + while (--l < n)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +
> +int a[3200], b[3200];
> +int fail;
> +
> +int
> +main ()
> +{
> + unsigned l, n;
> + unsigned res;
> + /* l > n*/
> + n = UINT_MAX - 64;
> + l = n + 32;
> + res = foo (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + l = n;
> + res = foo (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + l = n - 1;
> + res = foo (a, b, l, n);
> + if (res != l + 1)
> + fail++;
> +
> + l = n - 32;
> + res = foo (a, b, l, n);
> + if (res != l + 1)
> + fail++;
> +
> + l = UINT_MAX;
> + res = foo (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + l = n + 32;
> + res = foo_1 (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + l = n + 32;
> + res = foo_2 (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + l = n;
> + res = foo_3 (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + l = n - 1;
> + res = foo_3 (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + l = n - 2;
> + res = foo_3 (a, b, l, n);
> + if (res != l + 1)
> + fail++;
> +
> + res = foo_5 (a, b, l, n);
> + if (res != 0)
> + fail++;
> +
> + n = 64;
> + l = n - 32;
> + res = bar (a, b, l, n);
> + res++;
> + if (res != 0)
> + fail++;
> +
> + l = n;
> + res = bar (a, b, l, n);
> + res++;
> + if (res != 0)
> + fail++;
> +
> + l = n + 1;
> + res = bar (a, b, l, n);
> + res++;
> + if (res != l)
> + fail++;
> +
> + l = 0;
> + res = bar (a, b, l, n);
> + res++;
> + if (res != l)
> + fail++;
> +
> + l = 32;
> + res = bar_1 (a, b, l, n);
> + res++;
> + if (res != 0)
> + fail++;
> +
> + res = bar_1 (a, b, l, n);
> + res++;
> + if (res != 0)
> + fail++;
> +
> + if (fail)
> + __builtin_abort ();
> + return 0;
> +}
> +
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 7 "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/pr101145.inc
> b/gcc/testsuite/gcc.dg/vect/pr101145.inc
> new file mode 100644
> index 00000000000..6eed3fa8aca
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145.inc
> @@ -0,0 +1,63 @@
> +TYPE __attribute__ ((noinline))
> +foo_sign (int *__restrict__ a, int *__restrict__ b, TYPE l, TYPE n)
> +{
> + for (l = L_BASE; n < l; l += C)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +TYPE __attribute__ ((noinline))
> +bar_sign (int *__restrict__ a, int *__restrict__ b, TYPE l, TYPE n)
> +{
> + for (l = L_BASE_DOWN; l < n; l -= C)
> + *a++ = *b++ + 1;
> + return l;
> +}
> +
> +int __attribute__ ((noinline)) neq (int a, int b) { return a != b; }
> +
> +int a[1000], b[1000];
> +int fail;
> +
> +int
> +main ()
> +{
> + TYPE res;
> + TYPE l;
> + TYPE n;
> + n = N_BASE;
> + l = n - C;
> + res = foo_sign (a, b, l, n);
> + if (res != l)
> + fail++;
> +
> + l = n;
> + res = foo_sign (a, b, l, n);
> + if (res != l)
> + fail++;
> +
> + l = n + C;
> + res = foo_sign (a, b, l, n);
> + if (neq ((res - MIN) / C, 0))
> + fail++;
> +
> + n = N_BASE_DOWN;
> + l = n - C;
> + res = bar_sign (a, b, l, n);
> + if (neq ((MAX - res) / C, 0))
> + fail++;
> +
> + l = n;
> + res = bar_sign (a, b, l, n);
> + if (res != l)
> + fail++;
> +
> + l = n + C;
> + res = bar_sign (a, b, l, n);
> + if (res != l)
> + fail++;
> +
> + if (fail)
> + __builtin_abort ();
> + return 0;
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/pr101145_1.c
> b/gcc/testsuite/gcc.dg/vect/pr101145_1.c
> new file mode 100644
> index 00000000000..94f6b99b893
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145_1.c
> @@ -0,0 +1,15 @@
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-options "-O3 -fdump-tree-vect-details" } */
> +#define TYPE signed char
> +#define MIN -128
> +#define MAX 127
> +#define N_BASE (MAX - 32)
> +#define N_BASE_DOWN (MIN + 32)
> +
> +#define C 3
> +#define L_BASE l
> +#define L_BASE_DOWN l
> +
> +#include "pr101145.inc"
> +
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/pr101145_2.c
> b/gcc/testsuite/gcc.dg/vect/pr101145_2.c
> new file mode 100644
> index 00000000000..d3cfc9e01e1
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145_2.c
> @@ -0,0 +1,15 @@
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-options "-O3 -fdump-tree-vect-details" } */
> +#define TYPE unsigned char
> +#define MIN 0
> +#define MAX 255
> +#define N_BASE (MAX - 32 + 1)
> +#define N_BASE_DOWN (MIN + 32)
> +
> +#define C 2
> +#define L_BASE l
> +#define L_BASE_DOWN l
> +
> +#include "pr101145.inc"
> +
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" } } */
> diff --git a/gcc/testsuite/gcc.dg/vect/pr101145_3.c
> b/gcc/testsuite/gcc.dg/vect/pr101145_3.c
> new file mode 100644
> index 00000000000..e2cf9b1f7e6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145_3.c
> @@ -0,0 +1,15 @@
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-options "-O3 -fdump-tree-vect-details" } */
> +#define TYPE int *
> +#define MIN ((TYPE)0)
> +#define MAX ((TYPE)((long long)-1))
> +#define N_BASE ((TYPE) (-32))
> +#define N_BASE_DOWN (MIN + 32)
> +
> +#define C 1
> +#define L_BASE l
> +#define L_BASE_DOWN l
> +
> +#include "pr101145.inc"
> +
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 2 "vect" } } */
> diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
> index b5add827018..06db6a36ef8 100644
> --- a/gcc/tree-ssa-loop-niter.c
> +++ b/gcc/tree-ssa-loop-niter.c
> @@ -1473,6 +1473,86 @@ assert_loop_rolls_lt (tree type, affine_iv *iv0,
> affine_iv *iv1,
> }
> }
>
> +/* Determines number of iterations of loop whose ending condition
> + is IV0 < IV1 which likes: {base, -C} < n, or n < {base, C}.
> + The number of iterations is stored to NITER. */
> +
> +static bool
> +number_of_iterations_until_wrap (class loop *, tree type, affine_iv *iv0,
> + affine_iv *iv1, class tree_niter_desc *niter)
> +{
> + tree niter_type = unsigned_type_for (type);
> + tree max, min;
> +
> + if (POINTER_TYPE_P (type))
> + {
> + max = fold_convert (type, TYPE_MAX_VALUE (niter_type));
> + min = fold_convert (type, TYPE_MIN_VALUE (niter_type));
> + }
> + else
> + {
> + max = TYPE_MAX_VALUE (type);
> + min = TYPE_MIN_VALUE (type);
> + }
It would be cheaper to use wide_int here - wi::min/max_value
(TYPE_PRECISION (...), TYPE_SIGN (...)) and in the simplification
code below.
> + tree high = max, low = min, one = build_int_cst (niter_type, 1);
> + tree step;
> +
> + /* n < {base, C}. */
> + if (integer_zerop (iv0->step) && TREE_CODE (iv1->step) == INTEGER_CST
> + && !tree_int_cst_sign_bit (iv1->step))
> + {
> + step = iv1->step;
> + niter->niter = fold_build2 (MINUS_EXPR, niter_type, max, iv1->base);
> + if (TREE_CODE (iv1->base) == INTEGER_CST)
> + low = fold_build2 (MINUS_EXPR, type, iv1->base, one);
> + else if (TREE_CODE (iv0->base) == INTEGER_CST)
> + low = iv0->base;
> + }
> + /* {base, -C} < n. */
> + else if (TREE_CODE (iv0->step) == INTEGER_CST
> + && tree_int_cst_sign_bit (iv0->step) && integer_zerop (iv1->step))
> + {
> + step = fold_build1 (NEGATE_EXPR, TREE_TYPE (iv0->step), iv0->step);
> + niter->niter = fold_build2 (MINUS_EXPR, niter_type, iv0->base, min);
> + if (TREE_CODE (iv0->base) == INTEGER_CST)
> + high = fold_build2 (PLUS_EXPR, type, iv0->base, one);
> + else if (TREE_CODE (iv1->base) == INTEGER_CST)
> + high = iv1->base;
> + }
> + else
> + return false;
> +
> + /* (delta + step - 1) / step */
> + step = fold_convert (niter_type, step);
> + niter->niter = fold_convert (niter_type, niter->niter);
> + niter->niter = fold_build2 (PLUS_EXPR, niter_type, niter->niter, step);
> + niter->niter = fold_build2 (FLOOR_DIV_EXPR, niter_type, niter->niter,
> step);
> +
> + tree m = fold_build2 (MINUS_EXPR, niter_type, high, low);
> + m = fold_convert (niter_type, m);
> + mpz_t mstep, tmp, mmax;
> + mpz_init (mstep);
> + mpz_init (tmp);
> + mpz_init (mmax);
> + wi::to_mpz (wi::to_wide (step), mstep, UNSIGNED);
> + wi::to_mpz (wi::to_wide (m), mmax, UNSIGNED);
> + mpz_add (tmp, mmax, mstep);
> + mpz_sub_ui (tmp, tmp, 1);
> + mpz_fdiv_q (tmp, tmp, mstep);
> + niter->max = widest_int::from (wi::from_mpz (niter_type, tmp, false),
> + TYPE_SIGN (niter_type));
> + mpz_clear (mstep);
> + mpz_clear (tmp);
You forget to clear mmax? I wonder why you need to involve GMP here
at all since this is just add/sub/divide - you could use
widest_int directly I think. At least the back-and-forth between
trees, wide-int and mpz looks odd.
Richard.
> + niter->may_be_zero
> + = fold_build2 (LE_EXPR, boolean_type_node, iv1->base, iv0->base);
> +
> + niter->control.no_overflow = false;
> +
> + return true;
> +}
> +
> /* Determines number of iterations of loop whose ending condition
> is IV0 < IV1. TYPE is the type of the iv. The number of
> iterations is stored to NITER. BNDS bounds the difference
> @@ -1501,6 +1581,11 @@ number_of_iterations_lt (class loop *loop, tree type,
> affine_iv *iv0,
> niter->bound = iv0->base;
> }
>
> + /* {base, -C} < n, or n < {base, C} */
> + if (tree_int_cst_sign_bit (iv0->step)
> + || (!integer_zerop (iv1->step) && !tree_int_cst_sign_bit (iv1->step)))
> + return number_of_iterations_until_wrap (loop, type, iv0, iv1, niter);
> +
> delta = fold_build2 (MINUS_EXPR, niter_type,
> fold_convert (niter_type, iv1->base),
> fold_convert (niter_type, iv0->base));
> @@ -1665,62 +1750,6 @@ dump_affine_iv (FILE *file, affine_iv *iv)
> }
> }
>
> -/* Given exit condition IV0 CODE IV1 in TYPE, this function adjusts
> - the condition for loop-until-wrap cases. For example:
> - (unsigned){8, -1}_loop < 10 => {0, 1} != 9
> - 10 < (unsigned){0, max - 7}_loop => {0, 1} != 8
> - Return true if condition is successfully adjusted. */
> -
> -static bool
> -adjust_cond_for_loop_until_wrap (tree type, affine_iv *iv0, tree_code *code,
> - affine_iv *iv1)
> -{
> - /* Only support simple cases for the moment. */
> - if (TREE_CODE (iv0->base) != INTEGER_CST
> - || TREE_CODE (iv1->base) != INTEGER_CST)
> - return false;
> -
> - tree niter_type = unsigned_type_for (type), high, low;
> - /* Case: i-- < 10. */
> - if (integer_zerop (iv1->step))
> - {
> - /* TODO: Should handle case in which abs(step) != 1. */
> - if (!integer_minus_onep (iv0->step))
> - return false;
> - /* Give up on infinite loop. */
> - if (*code == LE_EXPR
> - && tree_int_cst_equal (iv1->base, TYPE_MAX_VALUE (type)))
> - return false;
> - high = fold_build2 (PLUS_EXPR, niter_type,
> - fold_convert (niter_type, iv0->base),
> - build_int_cst (niter_type, 1));
> - low = fold_convert (niter_type, TYPE_MIN_VALUE (type));
> - }
> - else if (integer_zerop (iv0->step))
> - {
> - /* TODO: Should handle case in which abs(step) != 1. */
> - if (!integer_onep (iv1->step))
> - return false;
> - /* Give up on infinite loop. */
> - if (*code == LE_EXPR
> - && tree_int_cst_equal (iv0->base, TYPE_MIN_VALUE (type)))
> - return false;
> - high = fold_convert (niter_type, TYPE_MAX_VALUE (type));
> - low = fold_build2 (MINUS_EXPR, niter_type,
> - fold_convert (niter_type, iv1->base),
> - build_int_cst (niter_type, 1));
> - }
> - else
> - gcc_unreachable ();
> -
> - iv0->base = low;
> - iv0->step = fold_convert (niter_type, integer_one_node);
> - iv1->base = high;
> - iv1->step = build_int_cst (niter_type, 0);
> - *code = NE_EXPR;
> - return true;
> -}
> -
> /* Determine the number of iterations according to condition (for staying
> inside loop) which compares two induction variables using comparison
> operator CODE. The induction variable on left side of the comparison
> @@ -1855,15 +1884,6 @@ number_of_iterations_cond (class loop *loop,
> return true;
> }
>
> - /* Handle special case loops: while (i-- < 10) and while (10 < i++) by
> - adjusting iv0, iv1 and code. */
> - if (code != NE_EXPR
> - && (tree_int_cst_sign_bit (iv0->step)
> - || (!integer_zerop (iv1->step)
> - && !tree_int_cst_sign_bit (iv1->step)))
> - && !adjust_cond_for_loop_until_wrap (type, iv0, &code, iv1))
> - return false;
> -
> /* OK, now we know we have a senseful loop. Handle several cases,
> depending
> on what comparison operator is used. */
> bound_difference (loop, iv1->base, iv0->base, &bnds);
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
