Re: [PATCH v2] Analyze niter for until-wrap condition [PR101145]

[guojiufu <guojiufu@linux.ibm.com>]

Hi,

I would like to have an early ping on this with more mail addresses.

BR,
Jiufu.

On 2021-07-07 20:47, Jiufu Guo wrote:
> Changes since v1:
> * Update assumptions for niter, add more test cases check
> * Use widest_int/wide_int instead mpz to do +-/
> * Move some early check for quick return
> 
> 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.
> 
> 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, x86_64 and aarch64.
> Is this ok for trunk?
> 
> gcc/ChangeLog:
> 
> 2021-07-07  Jiufu Guo  <guojiufu@linux.ibm.com>
> 
> 	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:
> 
> 2021-07-07  Jiufu Guo  <guojiufu@linux.ibm.com>
> 
> 	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.dg/vect/pr101145inf.c: New test.
> 	* gcc.dg/vect/pr101145inf.inc: New test.
> 	* gcc.dg/vect/pr101145inf_1.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/testsuite/gcc.dg/vect/pr101145inf.c   |  25 +++
>  gcc/testsuite/gcc.dg/vect/pr101145inf.inc |  28 ++++
>  gcc/testsuite/gcc.dg/vect/pr101145inf_1.c |  23 +++
>  gcc/tree-ssa-loop-niter.c                 | 157 ++++++++++--------
>  9 files changed, 463 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
>  create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145inf.c
>  create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145inf.inc
>  create mode 100644 gcc/testsuite/gcc.dg/vect/pr101145inf_1.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..9d5863726a5
> --- /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 (MIN - 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/testsuite/gcc.dg/vect/pr101145inf.c
> b/gcc/testsuite/gcc.dg/vect/pr101145inf.c
> new file mode 100644
> index 00000000000..ed49f5670b5
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145inf.c
> @@ -0,0 +1,25 @@
> +/* { dg-do run { target *-*-linux* *-*-gnu* *-*-uclinux* } } */
> +/* { dg-options "-O3" } */
> +#include <limits.h>
> +#include "pr101145inf.inc"
> +
> +__attribute__ ((noinline))
> +unsigned foo(unsigned val, unsigned start)
> +{
> +  unsigned cnt = 0;
> +  for (unsigned i = start; val <= i; i+=16)
> +    cnt++;
> +  return cnt;
> +}
> +
> +void test_finite ()
> +{
> +  unsigned n = foo (16, UINT_MAX - 32);
> +  if (n != 3)
> +    __builtin_abort ();
> +}
> +
> +void test_infinite ()
> +{
> + foo (15, UINT_MAX - 32);
> +}
> diff --git a/gcc/testsuite/gcc.dg/vect/pr101145inf.inc
> b/gcc/testsuite/gcc.dg/vect/pr101145inf.inc
> new file mode 100644
> index 00000000000..4aa3d049187
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145inf.inc
> @@ -0,0 +1,28 @@
> +#include <unistd.h>
> +#include <signal.h>
> +#include <stdlib.h>
> +
> +void test_finite ();
> +void test_infinite ();
> +
> +void do_exit (int i)
> +{
> +  exit (0);
> +}
> +
> +int main(void)
> +{
> +  test_finite ();
> +  struct sigaction s;
> +  sigemptyset (&s.sa_mask);
> +  s.sa_handler = do_exit;
> +  s.sa_flags = 0;
> +  sigaction (SIGALRM, &s, NULL);
> +  alarm (1);
> +
> +  test_infinite ();
> +
> +  __builtin_abort ();
> +  return 1;
> +}
> +
> diff --git a/gcc/testsuite/gcc.dg/vect/pr101145inf_1.c
> b/gcc/testsuite/gcc.dg/vect/pr101145inf_1.c
> new file mode 100644
> index 00000000000..4ee3e31c7fe
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr101145inf_1.c
> @@ -0,0 +1,23 @@
> +/* { dg-do run { target *-*-linux* *-*-gnu* *-*-uclinux* } } */
> +/* { dg-options "-O3" } */
> +#include <limits.h>
> +#include "pr101145inf.inc"
> +
> +__attribute__ ((noinline))
> +unsigned foo(unsigned val, unsigned start)
> +{
> +  unsigned cnt = 0;
> +  for (unsigned i = start; i < val; i-=16)
> +    cnt++;
> +  return cnt;
> +}
> +
> +void test_finite ()
> +{
> +  foo (UINT_MAX - 15, 32);
> +}
> +
> +void test_infinite ()
> +{
> +  foo (UINT_MAX - 14, 32);
> +}
> diff --git a/gcc/tree-ssa-loop-niter.c b/gcc/tree-ssa-loop-niter.c
> index b5add827018..85c179be68d 100644
> --- a/gcc/tree-ssa-loop-niter.c
> +++ b/gcc/tree-ssa-loop-niter.c
> @@ -1473,6 +1473,93 @@ 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 step, num, assumptions, may_be_zero;
> +  wide_int high, low, max, min;
> +
> +  may_be_zero = fold_build2 (LE_EXPR, boolean_type_node, iv1->base, 
> iv0->base);
> +  if (integer_onep (may_be_zero))
> +    return false;
> +
> +  int prec = TYPE_PRECISION (type);
> +  signop sgn = TYPE_SIGN (type);
> +  min = wi::min_value (prec, sgn);
> +  max = wi::max_value (prec, sgn);
> +
> +  /* n < {base, C}. */
> +  if (integer_zerop (iv0->step) && !tree_int_cst_sign_bit (iv1->step))
> +    {
> +      step = iv1->step;
> +      /* MIN + C - 1 <= n.  */
> +      tree last = wide_int_to_tree (type, min + wi::to_wide (step) - 
> 1);
> +      assumptions = fold_build2 (LE_EXPR, boolean_type_node, last, 
> iv0->base);
> +      if (integer_zerop (assumptions))
> +	return false;
> +
> +      num = fold_build2 (MINUS_EXPR, niter_type, wide_int_to_tree 
> (type, max),
> +			 iv1->base);
> +      high = max;
> +      if (TREE_CODE (iv1->base) == INTEGER_CST)
> +	low = wi::to_wide (iv1->base) - 1;
> +      else if (TREE_CODE (iv0->base) == INTEGER_CST)
> +	low = wi::to_wide (iv0->base);
> +      else
> +	low = min;
> +    }
> +  /* {base, -C} < n.  */
> +  else if (tree_int_cst_sign_bit (iv0->step) && integer_zerop 
> (iv1->step))
> +    {
> +      step = fold_build1 (NEGATE_EXPR, TREE_TYPE (iv0->step), 
> iv0->step);
> +      /* MAX - C + 1 >= n.  */
> +      tree last = wide_int_to_tree (type, max - wi::to_wide (step) + 
> 1);
> +      assumptions = fold_build2 (GE_EXPR, boolean_type_node, last, 
> iv1->base);
> +      if (integer_zerop (assumptions))
> +	return false;
> +
> +      num = fold_build2 (MINUS_EXPR, niter_type, iv0->base,
> +			 wide_int_to_tree (type, min));
> +      low = min;
> +      if (TREE_CODE (iv0->base) == INTEGER_CST)
> +	high = wi::to_wide (iv0->base) + 1;
> +      else if (TREE_CODE (iv1->base) == INTEGER_CST)
> +	high = wi::to_wide (iv1->base);
> +      else
> +	high = max;
> +    }
> +  else
> +    return false;
> +
> +  /* (delta + step - 1) / step */
> +  step = fold_convert (niter_type, step);
> +  num = fold_convert (niter_type, num);
> +  num = fold_build2 (PLUS_EXPR, niter_type, num, step);
> +  niter->niter = fold_build2 (FLOOR_DIV_EXPR, niter_type, num, step);
> +
> +  widest_int delta, s;
> +  delta = widest_int::from (high, sgn) - widest_int::from (low, sgn);
> +  s = wi::to_widest (step);
> +  delta = delta + s - 1;
> +  niter->max = wi::udiv_floor (delta, s);
> +
> +  niter->may_be_zero = may_be_zero;
> +
> +  if (!integer_nonzerop (assumptions))
> +    niter->assumptions = fold_build2 (TRUTH_AND_EXPR, 
> boolean_type_node,
> +				      niter->assumptions, assumptions);
> +
> +  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 +1588,11 @@ 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 +1757,6 @@ 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 +1891,6 @@ 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);