re PR tree-optimization/79351 (Invalid tree PRE optimization around compound literal)

2018-11-28  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/79351
	* tree-ssa-sccvn.c (vn_reference_lookup_3): For assignments from
	empty CONSTRUCTORs ensure the store is at a constant position.

	* gcc.dg/torture/pr79351.c: New testcase.

From-SVN: r266551

gcc/ChangeLog

 2018-11-28  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/79351
+	* tree-ssa-sccvn.c (vn_reference_lookup_3): For assignments from
+	empty CONSTRUCTORs ensure the store is at a constant position.
+
+2018-11-28  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/88229
 	* tree-ssa.c (non_rewritable_mem_ref_base): Check DECL_SIZE_UNIT
 	is an INTEGER_CST before accessing it so.

gcc/testsuite/ChangeLog

+2018-11-28  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/79351
+	* gcc.dg/torture/pr79351.c: New testcase.
+
 2018-11-28  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/88189
@@ -13,7 +18,7 @@
 	PR c++/88215
 	* c-c++-common/ubsan/pr88215.c: New test.
 
-2018-10-19  Richard Biener  <rguenther@suse.de>
+2018-11-28  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/88182
 	* g++.dg/gomp/pr88182.C: Move from libgomp and use -fopenmp-simd.

gcc/testsuite/gcc.dg/torture/pr79351.c

+/* { dg-do run } */
+
+static struct state {
+    int k;
+    int dummy;
+} states[256];
+
+__attribute((noipa))
+static void
+ismatch(int n)
+{
+  for (int j=0; j<n; j++) {
+      states[j] = (struct state){0};
+      for (int i = 0; i <= j; i++) {
+	  states[i].k++;
+      }
+  }
+}
+
+int
+main()
+{
+  ismatch(2);
+  if (states[0].k != 2)
+    __builtin_abort();
+}

gcc/tree-ssa-sccvn.c

@@ -2115,6 +2115,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *vr_,
       base2 = get_ref_base_and_extent (gimple_assign_lhs (def_stmt),
 				       &offset2, &size2, &maxsize2, &reverse);
       if (known_size_p (maxsize2)
+	  && known_eq (maxsize2, size2)
 	  && operand_equal_p (base, base2, 0)
 	  && known_subrange_p (offset, maxsize, offset2, size2))
 	{