Enhance NARROW FLOAT_EXPR vectorization by truncating integer to lower precision.

Enhance NARROW FLOAT_EXPR vectorization by truncating integer to lower precision.

Similar like WIDEN FLOAT_EXPR, when direct_optab is not existed, try
intermediate integer type whenever gimple ranger can tell it's safe.

.i.e.
When there's no direct optab for vector long long -> vector float, but
the value range of integer can be represented as int, try vector int
-> vector float if availble.

gcc/ChangeLog:

	PR tree-optimization/108804
	* tree-vect-patterns.cc (vect_get_range_info): Remove static.
	* tree-vect-stmts.cc (vect_create_vectorized_demotion_stmts):
	Add new parameter narrow_src_p.
	(vectorizable_conversion): Enhance NARROW FLOAT_EXPR
	vectorization by truncating to lower precision.
	* tree-vectorizer.h (vect_get_range_info): New declare.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr108804.c: New test.