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[PATCH, RFC, rs6000] enable GIMPLE folding of vec_splat


Hi
Enable GIMPLE folding of the vec_splat() intrinsic.
    
For review.. feedback is expected. :-)
    
I came up with the following after spending some time poking around
at the tree_vec_extract() and vector_element() functions as seen
in tree-vect-generic.c looking for insights.  Some of this seems a
bit clunky to me yet, but this is functional as far as make-check
can tell, and is as far as I can get without additional input.
    
This uses the tree_vec_extract() function out of tree-vect-generic.c
to retrieve the splat value, which is a BIT_FIELD_REF.   That function is
made non-static as part of this change.

In review of the .gimple output, this folding takes a sample testcase
of 
	vector bool int testb_0  (vector bool int x)
	{
	  return vec_splat (x, 0b00000); 
	}
from:
testb_0 (__vector __bool int x)
{
  __vector __bool intD.1486 D.2855;

  _1 = VIEW_CONVERT_EXPR<__vector signed intD.1468>(xD.2778);
  _2 = __builtin_altivec_vspltwD.1919 (_1, 0);
  D.2855 = VIEW_CONVERT_EXPR<__vector __bool intD.1486>(_2);
  return D.2855;
}
to:
 testb_0 (__vector __bool int x)
{
  __vector __bool intD.1486 D.2855;

  _1 = VIEW_CONVERT_EXPR<__vector signed intD.1468>(xD.2778);
  D.2856 = BIT_FIELD_REF <_1, 32, 0>;
  _2 = {D.2856, D.2856, D.2856, D.2856};
  D.2855 = VIEW_CONVERT_EXPR<__vector __bool intD.1486>(_2);
  return D.2855;
}


Testcases are being posted as a separate patch.
    
OK for trunk?   
Thanks,
-Will
    
[gcc]
    
2018-08-07  Will Schmidt  <will_schmidt@vnet.ibm.com>
    
	* config/rs6000/rs6000.c (rs6000_gimple_fold_builtin): Add support for
	  early gimple folding of vec_splat().
	* tree-vect-generic.c: Remove static from tree_vec_extract() definition.
	* gimple-fold.h:  Add an extern define for tree_vec_extract().

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 35c32be..acc6b49 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -15764,10 +15764,56 @@ rs6000_gimple_fold_builtin (gimple_stmt_iterator *gsi)
 	 tree splat_tree = build_vector_from_val (TREE_TYPE (lhs), splat_value);
 	 g = gimple_build_assign (lhs, splat_tree);
 	 gimple_set_location (g, gimple_location (stmt));
 	 gsi_replace (gsi, g, true);
 	 return true;
+	}
+
+    /* Flavors of vec_splat.  */
+    // a = vec_splat (b, 0x3) ;  // a = { b[3],b[3],b[3],...};
+    case ALTIVEC_BUILTIN_VSPLTB:
+    case ALTIVEC_BUILTIN_VSPLTH:
+    case ALTIVEC_BUILTIN_VSPLTW:
+    case VSX_BUILTIN_XXSPLTD_V2DI:
+    case VSX_BUILTIN_XXSPLTD_V2DF:
+      {
+	arg0 = gimple_call_arg (stmt, 0); /* input vector.  */
+	arg1 = gimple_call_arg (stmt, 1); /* index into arg0.  */
+	/* Only fold the vec_splat_*() if arg1 is a constant
+	   5-bit unsigned literal.  */
+	if (TREE_CODE (arg1) != INTEGER_CST || TREE_INT_CST_LOW (arg1) > 0x1f)
+	  return false;
+
+	lhs = gimple_call_lhs (stmt);
+	tree lhs_type = TREE_TYPE (lhs);
+
+	tree splat;
+	if (TREE_CODE (arg0) == VECTOR_CST)
+	  splat = VECTOR_CST_ELT (arg0, TREE_INT_CST_LOW (arg1));
+	else
+	  {
+	    /* Determine (in bits) the length and start location of the
+	       splat value for a call to the tree_vec_extract helper.  */
+	    int tree_size_in_bits = TREE_INT_CST_LOW (size_in_bytes (lhs_type))
+				    * BITS_PER_UNIT;
+	    int splat_elem_size = tree_size_in_bits / VECTOR_CST_NELTS (arg0);
+	    int splat_start_bit = TREE_INT_CST_LOW (arg1) * splat_elem_size;
+	    /* Do not attempt to early-fold if the size + specified offset into
+	       the vector would touch outside of the source vector.  */
+	    if ((splat_start_bit + splat_elem_size) > tree_size_in_bits)
+	      return false;
+	    tree len = build_int_cst (bitsizetype, splat_elem_size);
+	    tree start = build_int_cst (bitsizetype, splat_start_bit);
+	    splat = tree_vec_extract (gsi, TREE_TYPE (lhs_type), arg0,
+				      len, start);
+	}
+	/* And finally, build the new vector.  */
+	tree splat_tree = build_vector_from_val (lhs_type, splat);
+	g = gimple_build_assign (lhs, splat_tree);
+	gimple_set_location (g, gimple_location (stmt));
+	gsi_replace (gsi, g, true);
+	return true;
       }
 
     /* vec_mergel (integrals).  */
     case ALTIVEC_BUILTIN_VMRGLH:
     case ALTIVEC_BUILTIN_VMRGLW:
diff --git a/gcc/gimple-fold.h b/gcc/gimple-fold.h
index 04e9bfa..e634180 100644
--- a/gcc/gimple-fold.h
+++ b/gcc/gimple-fold.h
@@ -59,10 +59,11 @@ extern tree gimple_fold_indirect_ref (tree);
 extern bool gimple_fold_builtin_sprintf (gimple_stmt_iterator *);
 extern bool gimple_fold_builtin_snprintf (gimple_stmt_iterator *);
 extern bool arith_code_with_undefined_signed_overflow (tree_code);
 extern gimple_seq rewrite_to_defined_overflow (gimple *);
 extern void replace_call_with_value (gimple_stmt_iterator *, tree);
+extern tree tree_vec_extract (gimple_stmt_iterator *, tree, tree, tree, tree);
 
 /* gimple_build, functionally matching fold_buildN, outputs stmts
    int the provided sequence, matching and simplifying them on-the-fly.
    Supposed to replace force_gimple_operand (fold_buildN (...), ...).  */
 extern tree gimple_build (gimple_seq *, location_t,
diff --git a/gcc/tree-vect-generic.c b/gcc/tree-vect-generic.c
index 909f790..1c9701d 100644
--- a/gcc/tree-vect-generic.c
+++ b/gcc/tree-vect-generic.c
@@ -118,11 +118,11 @@ build_word_mode_vector_type (int nunits)
 
 typedef tree (*elem_op_func) (gimple_stmt_iterator *,
 			      tree, tree, tree, tree, tree, enum tree_code,
 			      tree);
 
-static inline tree
+tree
 tree_vec_extract (gimple_stmt_iterator *gsi, tree type,
 		  tree t, tree bitsize, tree bitpos)
 {
   if (TREE_CODE (t) == SSA_NAME)
     {



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