tree-optimization/91123 - restore redundant store removal

Redundant store removal in FRE was restricted for correctness reasons.
The following extends correctness fixes required to memcpy/aggregate
copy translation.  The main change is that we no longer insert
references rewritten to cover such aggregate copies into the hashtable
but the original one.

2020-02-04  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/91123
	* tree-ssa-sccvn.c (vn_walk_cb_data::finish): New method.
	(vn_walk_cb_data::last_vuse): New member.
	(vn_walk_cb_data::saved_operands): Likewsie.
	(vn_walk_cb_data::~vn_walk_cb_data): Release saved_operands.
	(vn_walk_cb_data::push_partial_def): Use finish.
	(vn_reference_lookup_2): Update last_vuse and use finish if
	we've saved operands.
	(vn_reference_lookup_3): Use finish and update calls to
	push_partial_defs everywhere.  When translating through
	memcpy or aggregate copies save off operands and alias-set.
	(eliminate_dom_walker::eliminate_stmt): Restore VN_WALKREWRITE
	operation for redundant store removal.

	* gcc.dg/tree-ssa/ssa-fre-85.c: New testcase.

gcc/ChangeLog

 2020-02-04  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/91123
+	* tree-ssa-sccvn.c (vn_walk_cb_data::finish): New method.
+	(vn_walk_cb_data::last_vuse): New member.
+	(vn_walk_cb_data::saved_operands): Likewsie.
+	(vn_walk_cb_data::~vn_walk_cb_data): Release saved_operands.
+	(vn_walk_cb_data::push_partial_def): Use finish.
+	(vn_reference_lookup_2): Update last_vuse and use finish if
+	we've saved operands.
+	(vn_reference_lookup_3): Use finish and update calls to
+	push_partial_defs everywhere.  When translating through
+	memcpy or aggregate copies save off operands and alias-set.
+	(eliminate_dom_walker::eliminate_stmt): Restore VN_WALKREWRITE
+	operation for redundant store removal.
+
+2020-02-04  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/92819
 	* tree-ssa-forwprop.c (simplify_vector_constructor): Avoid
 	generating more stmts than before.

gcc/testsuite/ChangeLog

 2020-02-04  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/91123
+	* gcc.dg/tree-ssa/ssa-fre-85.c: New testcase.
+
+2020-02-04  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/92819
 	* gcc.target/i386/pr92819.c: New testcase.
 	* gcc.target/i386/pr92803.c: Adjust.

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-85.c

+/* { dg-do compile } */
+/* { dg-options "-O -fstrict-aliasing -fdump-tree-fre1-details" } */
+
+struct X { int i; int j; };
+
+struct X x, y;
+void foo ()
+{
+  x.i = 1;
+  y = x;
+  y.i = 1; // redundant
+}
+
+/* { dg-final { scan-tree-dump "Deleted redundant store y.i" "fre1" } } */