diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 3faed93..adc28aa 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -3035,6 +3035,27 @@ add_standard_iv_candidates (struct ivopts_data *data)
 		   build_int_cst (long_long_integer_type_node, 1), true, NULL);
 }
 
+/* Return true if STMT is the increment stmt for a biv.  BEFORE and AFTER
+   are the corresponding vars before and after increment.  */
+
+static bool
+increment_stmt_for_biv_p (gimple *stmt, tree before, tree after)
+{
+  enum tree_code code;
+
+  gcc_assert (is_gimple_assign (stmt));
+  gcc_assert (gimple_assign_lhs (stmt) == after);
+
+  code = gimple_assign_rhs_code (stmt);
+  if (code != PLUS_EXPR && code != MINUS_EXPR && code != POINTER_PLUS_EXPR)
+    return false;
+
+  if (gimple_assign_rhs1 (stmt) != before
+      && gimple_assign_rhs2 (stmt) != before)
+    return false;
+
+  return true;
+}
 
 /* Adds candidates bases on the old induction variable IV.  */
 
@@ -3078,7 +3099,11 @@ add_iv_candidate_for_biv (struct ivopts_data *data, struct iv *iv)
       /* Don't add candidate if it's from another PHI node because
 	 it's an affine iv appearing in the form of PEELED_CHREC.  */
       phi = SSA_NAME_DEF_STMT (def);
-      if (gimple_code (phi) != GIMPLE_PHI)
+      if (gimple_code (phi) == GIMPLE_PHI)
+	gcc_assert (gimple_bb (phi) == data->current_loop->header);
+      /* Don't add candidate if we don't know where biv's increment
+	 stmt is.  */
+      else if (increment_stmt_for_biv_p (phi, iv->ssa_name, def))
 	{
 	  cand = add_candidate_1 (data,
 				  iv->base, iv->step, true, IP_ORIGINAL, NULL,
@@ -3086,8 +3111,6 @@ add_iv_candidate_for_biv (struct ivopts_data *data, struct iv *iv)
 	  cand->var_before = iv->ssa_name;
 	  cand->var_after = def;
 	}
-      else
-	gcc_assert (gimple_bb (phi) == data->current_loop->header);
     }
 }
 
@@ -7053,20 +7076,14 @@ rewrite_use_nonlinear_expr (struct ivopts_data *data,
   if (cand->pos == IP_ORIGINAL
       && cand->incremented_at == use->stmt)
     {
-      enum tree_code stmt_code;
-
-      gcc_assert (is_gimple_assign (use->stmt));
-      gcc_assert (gimple_assign_lhs (use->stmt) == cand->var_after);
-
       /* Check whether we may leave the computation unchanged.
 	 This is the case only if it does not rely on other
 	 computations in the loop -- otherwise, the computation
 	 we rely upon may be removed in remove_unused_ivs,
 	 thus leading to ICE.  */
-      stmt_code = gimple_assign_rhs_code (use->stmt);
-      if (stmt_code == PLUS_EXPR
-	  || stmt_code == MINUS_EXPR
-	  || stmt_code == POINTER_PLUS_EXPR)
+      if (increment_stmt_for_biv_p (use->stmt,
+				    cand->var_before,
+				    cand->var_after))
 	{
 	  if (gimple_assign_rhs1 (use->stmt) == cand->var_before)
 	    op = gimple_assign_rhs2 (use->stmt);
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr68021.c b/gcc/testsuite/gcc.dg/tree-ssa/pr68021.c
new file mode 100644
index 0000000..f60b1ff
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr68021.c
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+char a;
+void fn1 (char *p1, int p2, int p3)
+{
+  int i, x;
+  for (i = 0; i < 10; i++)
+    {
+      for (x = 0; x < p3; x++)
+	{
+	  *p1 = a;
+	  p1--;
+	}
+      p1 += p2;
+    }
+}