vect: Use vect representative statement instead of original in patch recog [PR115060]

vect: Use vect representative statement instead of original in patch recog [PR115060]

Some utility functions (such as vect_look_through_possible_promotion) that are
to find out certain kind of direct or indirect definition SSA for a value, may
return the original one of the SSA, not its pattern representative SSA, even
pattern is involved. For example,

   a = (T1) patt_b;
   patt_b = (T2) c;        // b = ...
   patt_c = not-a-cast;    // c = ...

Given 'a', the mentioned function will return 'c', instead of 'patt_c'. This
subtlety would make some pattern recog code that is unaware of it mis-use the
original instead of the new pattern statement, which is inconsistent wth
processing logic of the pattern formation pass. This patch corrects the issue
by forcing another utility function (vect_get_internal_def) return the pattern
statement information to caller by default.

2024-05-23 Feng Xue <fxue@os.amperecomputing.com>

gcc/
	PR tree-optimization/115060
	* tree-vect-patterns.cc (vect_get_internal_def): Return statement for
	vectorization.
	(vect_widened_op_tree): Call vect_get_internal_def instead of look_def
	to get statement information.
	(vect_recog_widen_abd_pattern): No need to call vect_stmt_to_vectorize.