[PATCH] Simplify vec_unpack of uniform_vector_p constructors in match.pd.

["Roger Sayle" <roger@nextmovesoftware.com>]

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This patch simplifies vec_unpack_hi_expr/vec_unpack_lo_expr of a uniform
constructor or vec_duplicate operand.  The motivation is from PR 105621
where after optimization, we're left with:

  vect_cst__21 = {c_8(D), c_8(D), c_8(D), c_8(D)};
  vect_iftmp.7_4 = [vec_unpack_hi_expr] vect_cst__21;

It turns out that there are no constant folding/simplification patterns
in match.pd, but the above can be simplified further to the equivalent:

  _20 = (long int) c_8(D);
  vect_iftmp.7_4 = [vec_duplicate_expr] _20;

which on x86-64 results in one less instruction, replacing pshufd $0
then punpackhq, with punpcklqdq.  This transformation is also useful
for helping CSE to spot that unpack_hi and unpack_lo are equivalent.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check with no new failures.  Ok for mainline?


2022-05-21  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        * match.pd (simplify vec_unpack_hi): Simplify VEC_UNPACK_*_EXPR
        of uniform vector constructors and vec_duplicate.

gcc/testsuite/ChangeLog
        * g++.dg/vect/pr105621.cc: New test case.


Thanks in advance,
Roger
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diff --git a/gcc/match.pd b/gcc/match.pd
index c2fed9b..753c392 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -7800,6 +7800,22 @@ and,
  (if (TREE_CODE (@0) == SSA_NAME && num_imm_uses (@0) == 2)
   (minus (mult (vec_perm @1 @1 @3) @2) @4)))
 
+/* VEC_UNPACK_LO_EXPR and friends.  */
+(for unpack (vec_unpack_lo vec_unpack_float_lo vec_unpack_fix_trunc_lo
+	     vec_unpack_hi vec_unpack_float_hi vec_unpack_fix_trunc_hi)
+     opcode (convert float fix_trunc convert float fix_trunc)
+ (simplify
+  (unpack CONSTRUCTOR@0)
+  (with { tree ctor = (TREE_CODE (@0) == SSA_NAME
+		    ? gimple_assign_rhs1 (SSA_NAME_DEF_STMT (@0)) : @0);
+	  tree elt = uniform_vector_p (ctor);
+	  tree eltype = TREE_TYPE (type); }
+   (if (elt)
+    (vec_duplicate (opcode:eltype { elt; })))))
+ (simplify
+  (unpack (vec_duplicate @0))
+  (with { tree eltype = TREE_TYPE (type); }
+   (vec_duplicate (opcode:eltype @0)))))
 
 /* Match count trailing zeroes for simplify_count_trailing_zeroes in fwprop.
    The canonical form is array[((x & -x) * C) >> SHIFT] where C is a magic
diff --git a/gcc/testsuite/g++.dg/vect/pr105621.cc b/gcc/testsuite/g++.dg/vect/pr105621.cc
new file mode 100644
index 0000000..98e8fcd
--- /dev/null
+++ b/gcc/testsuite/g++.dg/vect/pr105621.cc
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+bool d;
+
+void test(unsigned short a, int b, unsigned c) {
+  for (int i = 2; i < 24; i += 3)
+    d = b ? a ? c : 2086607777901731118 : 0;
+}
+
+/* { dg-final { scan-tree-dump-not "vec_unpack" "optimized" } } */