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* tree-ssa-loop-niter.c (scev_probably_wraps_p): Reword a comment. 

From-SVN: r103152
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Sebastian Pop 2005-08-16 11:41:33 +02:00 committed by Sebastian Pop
parent 39c39be09e
commit 546ad2d9fc
2 changed files with 17 additions and 8 deletions
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gcc/ChangeLog
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@ -1,3 +1,7 @@
2005-08-16 Sebastian Pop <pop@cri.ensmp.fr>
* tree-ssa-loop-niter.c (scev_probably_wraps_p): Reword a comment.
2005-08-15 Richard Earnshaw <richard.earnshaw@arm.com>
PR target/23355

21
gcc/tree-ssa-loop-niter.c
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@ -1891,19 +1891,24 @@ scev_probably_wraps_p (tree type, tree base, tree step,
/* If AT_STMT represents a cast operation, we may not be able to
take advantage of the undefinedness of signed type evolutions.
implement-c.texi states: "For conversion to a type of width
N, the value is reduced modulo 2^N to be within range of the
type;"
See PR 21959 for a test case. Essentially, given a cast
operation
unsigned char i;
signed char i.0;
unsigned char uc;
signed char sc;
...
i.0_6 = (signed char) i_2;
if (i.0_6 < 0)
sc = (signed char) uc;
if (sc < 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. */
where uc and sc have the scev {0, +, 1}, we would consider uc to
wrap around, but not sc, because it is of a signed type. This
causes VRP to erroneously fold the predicate above because it
thinks that sc cannot be negative. */
if (at_stmt && TREE_CODE (at_stmt) == MODIFY_EXPR)
{
tree rhs = TREE_OPERAND (at_stmt, 1);