Clean up loop-closed PHIs after loop finalize

This patch propagates loop-closed PHIs them out at
loop_optimizer_finalize.  For some cases, to clean up loop-closed PHIs
would save efforts of optimization passes after loopdone.

Thanks,
Jiufu Guo.

gcc/ChangeLog:
2020-10-18  Jiufu Guo   <guojiufu@linux.ibm.com>

	* cfgloop.h (loop_optimizer_finalize): Add flag argument.
	* loop-init.c (loop_optimizer_finalize): Call clean_up_loop_closed_phi.
	* tree-cfgcleanup.h (clean_up_loop_closed_phi): New declare.
	* tree-ssa-loop.c (tree_ssa_loop_done): Call loop_optimizer_finalize
	with flag argument.
	* tree-ssa-propagate.c (clean_up_loop_closed_phi): New function.

gcc/testsuite/ChangeLog:
2020-10-18  Jiufu Guo   <guojiufu@linux.ibm.com>

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

1 files changed, 72 insertions, 0 deletions

diff --git a/gcc/tree-ssa-propagate.c b/gcc/tree-ssa-propagate.c
index 87dbf55..354057b 100644
--- a/gcc/tree-ssa-propagate.c
+++ b/gcc/tree-ssa-propagate.c
@@ -1549,3 +1549,75 @@ propagate_tree_value_into_stmt (gimple_stmt_iterator *gsi, tree val)
   else
     gcc_unreachable ();
 }
+
+/* Check exits of each loop in FUN, walk over loop closed PHIs in
+   each exit basic block and propagate degenerate PHIs.  */
+
+unsigned
+clean_up_loop_closed_phi (function *fun)
+{
+  unsigned i;
+  edge e;
+  gphi *phi;
+  tree rhs;
+  tree lhs;
+  gphi_iterator gsi;
+  struct loop *loop;
+
+  /* Avoid possibly quadratic work when scanning for loop exits across
+   all loops of a nest.  */
+  if (!loops_state_satisfies_p (LOOPS_HAVE_RECORDED_EXITS))
+    return 0;
+
+  /* Walk over loop in function.  */
+  FOR_EACH_LOOP_FN (fun, loop, 0)
+    {
+      /* Check each exit edege of loop.  */
+      auto_vec<edge> exits = get_loop_exit_edges (loop);
+      FOR_EACH_VEC_ELT (exits, i, e)
+	if (single_pred_p (e->dest))
+	  /* Walk over loop-closed PHIs.  */
+	  for (gsi = gsi_start_phis (e->dest); !gsi_end_p (gsi);)
+	    {
+	      phi = gsi.phi ();
+	      rhs = gimple_phi_arg_def (phi, 0);
+	      lhs = gimple_phi_result (phi);
+
+	      if (rhs && may_propagate_copy (lhs, rhs))
+		{
+		  /* Dump details.  */
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    {
+		      fprintf (dump_file, "  Replacing '");
+		      print_generic_expr (dump_file, lhs, dump_flags);
+		      fprintf (dump_file, "' with '");
+		      print_generic_expr (dump_file, rhs, dump_flags);
+		      fprintf (dump_file, "'\n");
+		    }
+
+		  use_operand_p use_p;
+		  imm_use_iterator iter;
+		  gimple *use_stmt;
+		  FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
+		    {
+		      FOR_EACH_IMM_USE_ON_STMT (use_p, iter)
+			replace_exp (use_p, rhs);
+		      update_stmt (use_stmt);
+
+		      /* Update the invariant flag for ADDR_EXPR if replacing
+			 a variable index with a constant.  */
+		      if (gimple_assign_single_p (use_stmt)
+			  && TREE_CODE (gimple_assign_rhs1 (use_stmt))
+			       == ADDR_EXPR)
+			recompute_tree_invariant_for_addr_expr (
+			  gimple_assign_rhs1 (use_stmt));
+		    }
+		  remove_phi_node (&gsi, true);
+		}
+	      else
+		gsi_next (&gsi);
+	    }
+    }
+
+  return 0;
+}