re PR tree-optimization/38885 (missed FRE with BIT_FIELD_REF and vectors)

2011-10-05  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/38885
	* tree-ssa-sccvn.c (vn_reference_lookup_3): Handle partial reads
	from constants.

	* gcc.dg/tree-ssa/ssa-fre-33.c: New testcase.

From-SVN: r179556

gcc/ChangeLog

+2011-10-05  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/38885
+	* tree-ssa-sccvn.c (vn_reference_lookup_3): Handle partial reads
+	from constants.
+
 2011-10-05  Bernd Schmidt  <bernds@codesourcery.com>
 
 	* doc/invoke.texi (-fshrink-wrap): Document.

gcc/testsuite/ChangeLog

+2011-10-05  Richard Guenther  <rguenther@suse.de>
+
+	PR tree-optimization/38885
+	* gcc.dg/tree-ssa/ssa-fre-33.c: New testcase.
+
 2011-10-05  Bernd Schmidt  <bernds@codesourcery.com>
 
 	* gcc.target/i386/sw-1.c: New test.

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-33.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-fre1-details" } */
+
+#define vector __attribute__((vector_size(16) ))
+
+struct {
+    float i;
+    vector float global_res;
+} s;
+float x;
+int main(int argc)
+{
+  vector float res = (vector float){0.0f,0.0f,0.0f,1.0f};
+  res += (vector float){1.0f,2.0f,3.0f,4.0f};
+  s.global_res = res;
+  x = *((float*)&s.global_res + 1);
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump "Replaced BIT_FIELD_REF.*with 2" "fre1" } } */
+/* { dg-final { cleanup-tree-dump "fre1" } } */

gcc/tree-ssa-sccvn.c

@@ -1442,7 +1442,54 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *vr_)
 	}
     }
 
-  /* 3) For aggregate copies translate the reference through them if
+  /* 3) Assignment from a constant.  We can use folds native encode/interpret
+     routines to extract the assigned bits.  */
+  else if (CHAR_BIT == 8 && BITS_PER_UNIT == 8
+	   && ref->size == maxsize
+	   && maxsize % BITS_PER_UNIT == 0
+	   && offset % BITS_PER_UNIT == 0
+	   && is_gimple_reg_type (vr->type)
+	   && gimple_assign_single_p (def_stmt)
+	   && is_gimple_min_invariant (gimple_assign_rhs1 (def_stmt)))
+    {
+      tree base2;
+      HOST_WIDE_INT offset2, size2, maxsize2;
+      base2 = get_ref_base_and_extent (gimple_assign_lhs (def_stmt),
+				       &offset2, &size2, &maxsize2);
+      if (maxsize2 != -1
+	  && maxsize2 == size2
+	  && size2 % BITS_PER_UNIT == 0
+	  && offset2 % BITS_PER_UNIT == 0
+	  && operand_equal_p (base, base2, 0)
+	  && offset2 <= offset
+	  && offset2 + size2 >= offset + maxsize)
+	{
+	  /* We support up to 512-bit values (for V8DFmode).  */
+	  unsigned char buffer[64];
+	  int len;
+
+	  len = native_encode_expr (gimple_assign_rhs1 (def_stmt),
+				    buffer, sizeof (buffer));
+	  if (len > 0)
+	    {
+	      tree val = native_interpret_expr (vr->type,
+						buffer
+						+ ((offset - offset2)
+						   / BITS_PER_UNIT),
+						ref->size / BITS_PER_UNIT);
+	      if (val)
+		{
+		  unsigned int value_id = get_or_alloc_constant_value_id (val);
+		  return vn_reference_insert_pieces
+		           (vuse, vr->set, vr->type,
+			    VEC_copy (vn_reference_op_s, heap, vr->operands),
+			    val, value_id);
+		}
+	    }
+	}
+    }
+
+  /* 4) For aggregate copies translate the reference through them if
      the copy kills ref.  */
   else if (vn_walk_kind == VN_WALKREWRITE
 	   && gimple_assign_single_p (def_stmt)
@@ -1540,7 +1587,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *vr_)
       return NULL;
     }
 
-  /* 4) For memcpy copies translate the reference through them if
+  /* 5) For memcpy copies translate the reference through them if
      the copy kills ref.  */
   else if (vn_walk_kind == VN_WALKREWRITE
 	   && is_gimple_reg_type (vr->type)