The following fixes PR57343 - niter analysis uses multiple_of_p to
check whether a value is a multiple of another, but multiple_of_p
does not refrain from returning true for a * 10 and 10 even when
the multiplication may overflow (and changing that would pessimize
some callers at least while possibly fixing a latent bug in
extract_mul_div). So the following guards the use of
multiple_of_p in niter analysis properly and implements the
important special-cases for wrapping types.
Bootstrapped and tested on x86_64-unknown-linux-gnu, ok for trunk?
Thanks,
Richard.
2013-05-27 Richard Biener <rguent...@suse.de>
PR tree-optimization/57343
* tree-ssa-loop-niter.c (number_of_iterations_ne_max): Do not
use multiple_of_p if not TYPE_OVERFLOW_UNDEFINED.
(number_of_iterations_cond): Do not build the folded tree.
* gcc.dg/torture/pr57343.c: New testcase.
Index: gcc/tree-ssa-loop-niter.c
===================================================================
*** gcc/tree-ssa-loop-niter.c (revision 199350)
--- gcc/tree-ssa-loop-niter.c (working copy)
*************** number_of_iterations_ne_max (mpz_t bnd,
*** 552,561 ****
{
double_int max;
mpz_t d;
bool bnds_u_valid = ((no_overflow && exit_must_be_taken)
|| mpz_sgn (bnds->below) >= 0);
! if (multiple_of_p (TREE_TYPE (c), c, s))
{
/* If C is an exact multiple of S, then its value will be reached before
the induction variable overflows (unless the loop is exited in some
--- 552,569 ----
{
double_int max;
mpz_t d;
+ tree type = TREE_TYPE (c);
bool bnds_u_valid = ((no_overflow && exit_must_be_taken)
|| mpz_sgn (bnds->below) >= 0);
! if (integer_onep (s)
! || (TREE_CODE (c) == INTEGER_CST
! && TREE_CODE (s) == INTEGER_CST
! && tree_to_double_int (c).mod (tree_to_double_int (s),
! TYPE_UNSIGNED (type),
! EXACT_DIV_EXPR).is_zero ())
! || (TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (c))
! && multiple_of_p (type, c, s)))
{
/* If C is an exact multiple of S, then its value will be reached before
the induction variable overflows (unless the loop is exited in some
*************** number_of_iterations_ne_max (mpz_t bnd,
*** 572,587 ****
the whole # of iterations analysis will fail). */
if (!no_overflow)
{
! max = double_int::mask (TYPE_PRECISION (TREE_TYPE (c))
! - tree_low_cst (num_ending_zeros (s), 1));
mpz_set_double_int (bnd, max, true);
return;
}
/* Now we know that the induction variable does not overflow, so the loop
iterates at most (range of type / S) times. */
! mpz_set_double_int (bnd, double_int::mask (TYPE_PRECISION (TREE_TYPE (c))),
! true);
/* If the induction variable is guaranteed to reach the value of C before
overflow, ... */
--- 580,594 ----
the whole # of iterations analysis will fail). */
if (!no_overflow)
{
! max = double_int::mask (TYPE_PRECISION (type)
! - tree_low_cst (num_ending_zeros (s), 1));
mpz_set_double_int (bnd, max, true);
return;
}
/* Now we know that the induction variable does not overflow, so the loop
iterates at most (range of type / S) times. */
! mpz_set_double_int (bnd, double_int::mask (TYPE_PRECISION (type)), true);
/* If the induction variable is guaranteed to reach the value of C before
overflow, ... */
*************** number_of_iterations_cond (struct loop *
*** 1311,1317 ****
}
/* If the loop exits immediately, there is nothing to do. */
! if (integer_zerop (fold_build2 (code, boolean_type_node, iv0->base,
iv1->base)))
{
niter->niter = build_int_cst (unsigned_type_for (type), 0);
niter->max = double_int_zero;
--- 1318,1325 ----
}
/* If the loop exits immediately, there is nothing to do. */
! tree tem = fold_binary (code, boolean_type_node, iv0->base, iv1->base);
! if (tem && integer_zerop (tem))
{
niter->niter = build_int_cst (unsigned_type_for (type), 0);
niter->max = double_int_zero;
Index: gcc/testsuite/gcc.dg/torture/pr57343.c
===================================================================
*** gcc/testsuite/gcc.dg/torture/pr57343.c (revision 0)
--- gcc/testsuite/gcc.dg/torture/pr57343.c (working copy)
***************
*** 0 ****
--- 1,22 ----
+ /* { dg-do run } */
+
+ int c = 0;
+
+ int
+ main ()
+ {
+ int i, f = 1;
+ for (i = 0; i < 5; i++)
+ {
+ --c;
+ unsigned char h = c * 100;
+ if (h == 0)
+ {
+ f = 0;
+ break;
+ }
+ }
+ if (f != 1)
+ __builtin_abort ();
+ return 0;
+ }
