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vect: Allow unsigned-to-signed promotion in vect_look_through_possible_promotion [PR115707]

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The function fails to figure out root definition if casts involves more than
two promotions with sign change as:

long a = (long)b;       // promotion cast
 -> int b = (int)c;     // promotion cast, sign change
   -> unsigned short c = ...;

For this case, the function thinks the 2nd cast has different sign as the 1st,
so stop looking through, while "unsigned short -> integer" is a nature sign
extension.

2024-08-05 Feng Xue <fxue@os.amperecomputing.com>

gcc/
	PR tree-optimization/115707
	* tree-vect-patterns.cc (vect_look_through_possible_promotion): Allow
	unsigned-to-signed promotion.
This commit is contained in:
Feng Xue 2024-08-05 15:23:56 +08:00
parent 0355c943b9
commit 3c089ee5d5
1 changed files with 3 additions and 1 deletions
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4
gcc/tree-vect-patterns.cc
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@ -434,7 +434,9 @@ vect_look_through_possible_promotion (vec_info *vinfo, tree op,
sign of the previous promotion. */
if (!res
|| TYPE_PRECISION (unprom->type) == orig_precision
|| TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type))
|| TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type)
|| (TYPE_UNSIGNED (op_type)
&& TYPE_PRECISION (op_type) < TYPE_PRECISION (unprom->type)))
{
unprom->set_op (op, dt, caster);
min_precision = TYPE_PRECISION (op_type);