slp: fix sharing of SLP only patterns.

slp: fix sharing of SLP only patterns.

The attached testcase ICEs due to a couple of issues.
In the testcase you have two SLP instances that share the majority of their
definition with each other.  One tree defines a COMPLEX_MUL sequence and the
other tree a COMPLEX_FMA.

The ice happens because:

1. the refcounts are wrong, in particular the FMA case doesn't correctly count
the references for the COMPLEX_MUL that it consumes.

2. when the FMA is created it incorrectly assumes it can just tear apart the MUL
node that it's consuming.  This is wrong and should only be done when there is
no more uses of the node, in which case the vector only pattern is no longer
relevant.

To fix the last part the SLP only pattern reset code was moved into
vect_free_slp_tree which results in cleaner code.  I also think it does belong
there since that function knows when there are no more uses of the node and so
the pattern should be unmarked, so when the the vectorizer is inspecting the BB
it doesn't find the now invalid vector only patterns.

The patch also clears the SLP_TREE_REPRESENTATIVE when stores are removed such
that we don't hit an error later trying to free the stmt_vec_info again.

Lastly it also tweaks the results of whether a pattern has been detected or not
to return true when another SLP instance has created a pattern that is only used
by a different instance (due to the trees being unshared).

Instead of ICEing this code now produces

        adrp    x1, .LANCHOR0
        add     x2, x1, :lo12:.LANCHOR0
        movi    v1.2s, 0
        mov     w0, 0
        ldr     x4, [x1, #:lo12:.LANCHOR0]
        ldrsw   x3, [x2, 16]
        ldr     x1, [x2, 8]
        ldrsw   x2, [x2, 20]
        ldr     d0, [x4]
        ldr     d2, [x1, x3, lsl 3]
        fcmla   v2.2s, v0.2s, v0.2s, #0
        fcmla   v2.2s, v0.2s, v0.2s, #90
        str     d2, [x1, x3, lsl 3]
        fcmla   v1.2s, v0.2s, v0.2s, #0
        fcmla   v1.2s, v0.2s, v0.2s, #90
        str     d1, [x1, x2, lsl 3]
        ret

PS. This testcase actually shows that the codegen we get in these cases is not
optimal. It should generate a MUL + ADD instead MUL + FMA.

But that's for GCC 12.

gcc/ChangeLog:

	PR tree-optimization/99149
	* tree-vect-slp-patterns.c (vect_detect_pair_op): Don't recreate the
	buffer.
	(vect_slp_reset_pattern): Remove.
	(complex_fma_pattern::matches): Remove call to vect_slp_reset_pattern.
	(complex_mul_pattern::build, complex_fma_pattern::build,
	complex_fms_pattern::build): Fix ref counts.
	* tree-vect-slp.c (vect_free_slp_tree): Undo SLP only pattern relevancy
	when node is being deleted.
	(vect_match_slp_patterns_2): Correct result of cache hit on patterns.
	(vect_schedule_slp): Invalidate SLP_TREE_REPRESENTATIVE of removed
	stores.
	* tree-vectorizer.c (vec_info::new_stmt_vec_info): Initialize value.

gcc/testsuite/ChangeLog:

	PR tree-optimization/99149
	* g++.dg/vect/pr99149.cc: New test.