tree-optimization/94864 - vector insert of vector extract simplification

The PRs ask for optimizing of

  _1 = BIT_FIELD_REF <b_3(D), 64, 64>;
  result_4 = BIT_INSERT_EXPR <a_2(D), _1, 64>;

to a vector permutation.  The following implements this as
match.pd pattern, improving code generation on x86_64.

On the RTL level we face the issue that backend patterns inconsistently
use vec_merge and vec_select of vec_concat to represent permutes.

I think using a (supported) permute is almost always better
than an extract plus insert, maybe excluding the case we extract
element zero and that's aliased to a register that can be used
directly for insertion (not sure how to query that).

The patch FAILs one case in gcc.target/i386/avx512fp16-vmovsh-1a.c
where we now expand from

 __A_28 = VEC_PERM_EXPR <x2.8_9, x1.9_10, { 0, 9, 10, 11, 12, 13, 14, 15 }>;

instead of

 _28 = BIT_FIELD_REF <x2.8_9, 16, 0>;
 __A_29 = BIT_INSERT_EXPR <x1.9_10, _28, 0>;

producing a vpblendw instruction instead of the expected vmovsh.  That's
either a missed vec_perm_const expansion optimization or even better,
an improvement - Zen4 for example has 4 ports to execute vpblendw
but only 3 for executing vmovsh and both instructions have the same size.

The patch XFAILs the sub-testcase.

	PR tree-optimization/94864
	PR tree-optimization/94865
	PR tree-optimization/93080
	* match.pd (bit_insert @0 (BIT_FIELD_REF @1 ..) ..): New pattern
	for vector insertion from vector extraction.

	* gcc.target/i386/pr94864.c: New testcase.
	* gcc.target/i386/pr94865.c: Likewise.
	* gcc.target/i386/avx512fp16-vmovsh-1a.c: XFAIL.
	* gcc.dg/tree-ssa/forwprop-40.c: Likewise.
	* gcc.dg/tree-ssa/forwprop-41.c: Likewise.

1 files changed, 25 insertions, 0 deletions

diff --git a/gcc/match.pd b/gcc/match.pd
index 86fdc60..6e08302 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -8006,6 +8006,31 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 		      wi::to_wide (@ipos) + isize))
     (BIT_FIELD_REF @0 @rsize @rpos)))))
 
+/* Simplify vector inserts of other vector extracts to a permute.  */
+(simplify
+ (bit_insert @0 (BIT_FIELD_REF@2 @1 @rsize @rpos) @ipos)
+ (if (VECTOR_TYPE_P (type)
+      && types_match (@0, @1)
+      && types_match (TREE_TYPE (TREE_TYPE (@0)), TREE_TYPE (@2))
+      && TYPE_VECTOR_SUBPARTS (type).is_constant ())
+  (with
+   {
+     unsigned HOST_WIDE_INT elsz
+       = tree_to_uhwi (TYPE_SIZE (TREE_TYPE (TREE_TYPE (@1))));
+     poly_uint64 relt = exact_div (tree_to_poly_uint64 (@rpos), elsz);
+     poly_uint64 ielt = exact_div (tree_to_poly_uint64 (@ipos), elsz);
+     unsigned nunits = TYPE_VECTOR_SUBPARTS (type).to_constant ();
+     vec_perm_builder builder;
+     builder.new_vector (nunits, nunits, 1);
+     for (unsigned i = 0; i < nunits; ++i)
+       builder.quick_push (known_eq (ielt, i) ? nunits + relt : i);
+     vec_perm_indices sel (builder, 2, nunits);
+   }
+   (if (!VECTOR_MODE_P (TYPE_MODE (type))
+	|| can_vec_perm_const_p (TYPE_MODE (type), TYPE_MODE (type), sel, false))
+    (vec_perm @0 @1 { vec_perm_indices_to_tree
+                        (build_vector_type (ssizetype, nunits), sel); })))))
+
 (if (canonicalize_math_after_vectorization_p ())
  (for fmas (FMA)
   (simplify