sra: Fix access verification (PR 94598)

get_ref_base_and_extent recognizes ARRAY_REFs with variable index but
into arrays of length one as constant offset accesses.  However,
max_size in such cases is extended to span the whole element.  This
confuses SRA verification when SRA also builds its (total
scalarization) access structures to describe fields under such array -
get_ref_base_and_extent returns different size and max_size for them.

Fixed by not performing the check for total scalarization accesses.
The subsequent check then had to be changed to use size and not
max_size too, which meant it has to be skipped when the access
structure describes a genuine variable array access.

Bootstrapped and tested on x86_64-linux.

2020-04-16  Martin Jambor  <mjambor@suse.cz>

	PR tree-optimization/94598
	* tree-sra.c (verify_sra_access_forest): Fix verification of total
	scalarization accesses under access to one-element arrays.

	testsuite/
	* gcc.dg/tree-ssa/pr94598.c: New test.

gcc/ChangeLog

+2020-04-16  Martin Jambor  <mjambor@suse.cz>
+
+	PR tree-optimization/94598
+	* tree-sra.c (verify_sra_access_forest): Fix verification of total
+	scalarization accesses under access to one-element arrays.
+
 2020-04-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR bootstrap/89494

gcc/testsuite/ChangeLog

+2020-04-16  Martin Jambor  <mjambor@suse.cz>
+
+	PR tree-optimization/94598
+	* gcc.dg/tree-ssa/pr94598.c: New test.
+
 2020-04-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR ipa/92372

gcc/testsuite/gcc.dg/tree-ssa/pr94598.c

+/* { dg-do compile } */
+/* { dg-options "-O1" } */
+
+struct a {
+  int b;
+  short c;
+};
+int d;
+void e() {
+  struct a f[1];
+  f[d] = f[d];
+}
+
+struct S {
+  int a[30];
+  int c;
+};
+
+int get_int (void);
+
+int foo(struct S p)
+{
+  p.c = get_int ();
+  p.a[get_int()] = get_int()+1;
+  return p.c;
+}

gcc/tree-sra.c

@@ -2357,9 +2357,11 @@ verify_sra_access_forest (struct access *root)
       gcc_assert (base == first_base);
       gcc_assert (offset == access->offset);
       gcc_assert (access->grp_unscalarizable_region
+		  || access->grp_total_scalarization
 		  || size == max_size);
-      gcc_assert (!is_gimple_reg_type (access->type)
-		  || max_size == access->size);
+      gcc_assert (access->grp_unscalarizable_region
+		  || !is_gimple_reg_type (access->type)
+		  || size == access->size);
       gcc_assert (reverse == access->reverse);
 
       if (access->first_child)