tree-optimization/93946 - fix bogus redundant store removal in FRE, DSE and DOM

This fixes a common mistake in removing a store that looks redudnant but
is not because it changes the dynamic type of the memory and thus makes
a difference for following loads with TBAA.

2020-03-03  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/93946
	* alias.h (refs_same_for_tbaa_p): Declare.
	* alias.c (refs_same_for_tbaa_p): New function.
	* tree-ssa-alias.c (ao_ref_alias_set): For a NULL ref return
	zero.
	* tree-ssa-scopedtables.h
	(avail_exprs_stack::lookup_avail_expr): Add output argument
	giving access to the hashtable entry.
	* tree-ssa-scopedtables.c (avail_exprs_stack::lookup_avail_expr):
	Likewise.
	* tree-ssa-dom.c: Include alias.h.
	(dom_opt_dom_walker::optimize_stmt): Validate TBAA state before
	removing redundant store.
	* tree-ssa-sccvn.h (vn_reference_s::base_set): New member.
	(ao_ref_init_from_vn_reference): Adjust prototype.
	(vn_reference_lookup_pieces): Likewise.
	(vn_reference_insert_pieces): Likewise.
	* tree-ssa-sccvn.c: Track base alias set in addition to alias
	set everywhere.
	(eliminate_dom_walker::eliminate_stmt): Also check base alias
	set when removing redundant stores.
	(visit_reference_op_store): Likewise.
	* dse.c (record_store): Adjust valdity check for redundant
	store removal.

	* gcc.dg/torture/pr93946-1.c: New testcase.
	* gcc.dg/torture/pr93946-2.c: Likewise.

1 files changed, 31 insertions, 3 deletions

diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c
index 374143e..f2a4ed9 100644
--- a/gcc/tree-ssa-dse.c
+++ b/gcc/tree-ssa-dse.c
@@ -658,6 +658,17 @@ dse_optimize_redundant_stores (gimple *stmt)
 {
   int cnt = 0;
 
+  /* TBAA state of STMT, if it is a call it is effectively alias-set zero.  */
+  alias_set_type earlier_set = 0;
+  alias_set_type earlier_base_set = 0;
+  if (is_gimple_assign (stmt))
+    {
+      ao_ref lhs_ref;
+      ao_ref_init (&lhs_ref, gimple_assign_lhs (stmt));
+      earlier_set = ao_ref_alias_set (&lhs_ref);
+      earlier_base_set = ao_ref_base_alias_set (&lhs_ref);
+    }
+
   /* We could do something fairly complex and look through PHIs
      like DSE_CLASSIFY_STORE, but it doesn't seem to be worth
      the effort.
@@ -698,10 +709,27 @@ dse_optimize_redundant_stores (gimple *stmt)
 	    {
 	      gimple_stmt_iterator gsi = gsi_for_stmt (use_stmt);
 	      if (is_gimple_assign (use_stmt))
-		delete_dead_or_redundant_assignment (&gsi, "redundant",
-						     need_eh_cleanup);
+		{
+		  ao_ref lhs_ref;
+		  ao_ref_init (&lhs_ref, gimple_assign_lhs (use_stmt));
+		  if ((earlier_set == ao_ref_alias_set (&lhs_ref)
+		       || alias_set_subset_of (ao_ref_alias_set (&lhs_ref),
+					       earlier_set))
+		      && (earlier_base_set == ao_ref_base_alias_set (&lhs_ref)
+			  || alias_set_subset_of
+			       (ao_ref_base_alias_set (&lhs_ref),
+						  earlier_base_set)))
+		    delete_dead_or_redundant_assignment (&gsi, "redundant",
+							 need_eh_cleanup);
+		}
 	      else if (is_gimple_call (use_stmt))
-		delete_dead_or_redundant_call (&gsi, "redundant");
+		{
+		  if ((earlier_set == 0
+		       || alias_set_subset_of (0, earlier_set))
+		      && (earlier_base_set == 0
+			  || alias_set_subset_of (0, earlier_base_set)))
+		  delete_dead_or_redundant_call (&gsi, "redundant");
+		}
 	      else
 		gcc_unreachable ();
 	    }