RISC-V: avlprop: Do not propagate VL from slidedown.

In the following situation (found in the
rvv/autovec/vls-vlmax/shuffle-slide.c test which is not yet pushed)

	vsetivli	zero,4,e8,mf4,ta,ma
	vle8.v	v2,0(a1)			# (1)
	vle8.v	v1,0(a2)			# (2)
	vsetivli	zero,2,e8,mf4,tu,ma
	vslidedown.vi	v1,v2,2
	vsetivli	zero,4,e8,mf4,ta,ma
	vse8.v	v1,0(a2)

we wrongly "propagate" VL=2 from vslidedown into the load.

Although we check whether the "target" instruction has a merge operand
the check only handles cases where the merge operand itself is
loaded, like (2) in the snippet above.  For (1) we load the non-merged
operand, assume propagation is valid and continue despite (2).

This patch just re-uses avl_can_be_propagated_p in order to disable
slides altogether in such situations.

gcc/ChangeLog:

	* config/riscv/riscv-avlprop.cc (pass_avlprop::get_vlmax_ta_preferred_avl):
	Check whether the use insn is valid for propagation.

1 files changed, 2 insertions, 1 deletions

diff --git a/gcc/config/riscv/riscv-avlprop.cc b/gcc/config/riscv/riscv-avlprop.cc
index 91d80aa..62491f9 100644
--- a/gcc/config/riscv/riscv-avlprop.cc
+++ b/gcc/config/riscv/riscv-avlprop.cc
@@ -351,7 +351,8 @@ pass_avlprop::get_vlmax_ta_preferred_avl (insn_info *insn) const
 	  if (!use_insn->can_be_optimized () || use_insn->is_asm ()
 	      || use_insn->is_call () || use_insn->has_volatile_refs ()
 	      || use_insn->has_pre_post_modify ()
-	      || !has_vl_op (use_insn->rtl ()))
+	      || !has_vl_op (use_insn->rtl ())
+	      || !avl_can_be_propagated_p (use_insn->rtl ()))
 	    return NULL_RTX;
 
 	  /* We should only propagate non-VLMAX AVL into VLMAX insn when