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re PR tree-optimization/21959 (vrp miscompiles Ada front-end, drops loop exit test in well-defined wrap-around circumstances)

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PR 21959
	* tree-ssa-loop-niter.c (scev_probably_wraps_p): Handle type
	casts between unsigned and signed types with different size
	or precision.

testsuite/ChangeLog

	PR 21959
	* gcc.dg/tree-ssa/pr21959.c: New test.

From-SVN: r101365
This commit is contained in:
Diego Novillo 2005-06-28 00:52:35 +00:00 • committed by Diego Novillo
parent 5ab2b3e44e
commit 3eca1bd776
4 changed files with 67 additions and 0 deletions
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7
gcc/ChangeLog
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@ -1,3 +1,10 @@
2005-06-27 Diego Novillo <dnovillo@redhat.com>
PR 21959
* tree-ssa-loop-niter.c (scev_probably_wraps_p): Handle type
casts between unsigned and signed types with different size
or precision.
2005-06-28 Jan Hubicka <jh@suse.cz>
* tree-optimize.c (exercute_free_datastructures):

5
gcc/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2005-06-27 Diego Novillo <dnovillo@redhat.com>
PR 21959
* gcc.dg/tree-ssa/pr21959.c: New test.
2005-06-27 Jakub Jelinek <jakub@redhat.com>
* gcc.c-torture/execute/builtins/lib/main.c (abort): Add prototype.

20
gcc/testsuite/gcc.dg/tree-ssa/pr21959.c Normal file
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@ -0,0 +1,20 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-vrp" } */
unsigned char c[0xFF];
void f(void)
{
unsigned char i;
c[128] = 128;
i = 0;
while (1)
{
/* This predicate should not be folded out. */
if (((signed char) i) < 0) break;
c[i] = ' ';
i++;
}
}
/* { dg-final { scan-tree-dump-times "Folding predicate " 0 "vrp" } } */
/* { dg-final { cleanup-tree-dump "vrp" } } */

35
gcc/tree-ssa-loop-niter.c
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@ -1649,6 +1649,41 @@ scev_probably_wraps_p (tree type, tree base, tree step,
return true;
}
/* If AT_STMT represents a cast operation, we may not be able to
take advantage of the undefinedness of signed type evolutions.
See PR 21959 for a test case. Essentially, given a cast
operation
unsigned char i;
signed char i.0;
...
i.0_6 = (signed char) i_2;
if (i.0_6 < 0)
...
where i_2 and i.0_6 have the scev {0, +, 1}, we would consider
i_2 to wrap around, but not i.0_6, because it is of a signed
type. This causes VRP to erroneously fold the predicate above
because it thinks that i.0_6 cannot be negative. */
if (TREE_CODE (at_stmt) == MODIFY_EXPR)
{
tree rhs = TREE_OPERAND (at_stmt, 1);
tree outer_t = TREE_TYPE (rhs);
if (!TYPE_UNSIGNED (outer_t)
&& (TREE_CODE (rhs) == NOP_EXPR || TREE_CODE (rhs) == CONVERT_EXPR))
{
tree inner_t = TREE_TYPE (TREE_OPERAND (rhs, 0));
/* If the inner type is unsigned and its size and/or
precision are smaller to that of the outer type, then the
expression may wrap around. */
if (TYPE_UNSIGNED (inner_t)
&& (TYPE_SIZE (inner_t) <= TYPE_SIZE (outer_t)
|| TYPE_PRECISION (inner_t) <= TYPE_PRECISION (outer_t)))
return true;
}
}
/* After having set INIT_IS_MAX, we can return false: when not using
wrapping arithmetic, signed types don't wrap. */
if (!flag_wrapv && !TYPE_UNSIGNED (type))