re PR rtl-optimization/90257 (8% degradation on cpu2006 403.gcc starting with r270484)

	PR rtl-optimization/90257
	* cfgrtl.c (flow_active_insn_p): Return true for USE of a function
	return value.

	Revert the revert:
	2019-04-21  H.J. Lu  <hongjiu.lu@intel.com>

	PR target/90178
	Revert:
	2018-11-21  Uros Bizjak  <ubizjak@gmail.com>

	Revert the revert:
	2013-10-26  Vladimir Makarov  <vmakarov@redhat.com>

	Revert:
	2013-10-25  Vladimir Makarov  <vmakarov@redhat.com>

	* lra-spills.c (lra_final_code_change): Remove useless move insns.

From-SVN: r270653

gcc/ChangeLog

+2019-04-29  Jakub Jelinek  <jakub@redhat.com>
+
+	PR rtl-optimization/90257
+	* cfgrtl.c (flow_active_insn_p): Return true for USE of a function
+	return value.
+
+	Revert the revert:
+	2019-04-21  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR target/90178
+	Revert:
+	2018-11-21  Uros Bizjak  <ubizjak@gmail.com>
+
+	Revert the revert:
+	2013-10-26  Vladimir Makarov  <vmakarov@redhat.com>
+
+	Revert:
+	2013-10-25  Vladimir Makarov  <vmakarov@redhat.com>
+
+	* lra-spills.c (lra_final_code_change): Remove useless move insns.
+
 2019-04-29  Richard Biener  <rguenther@suse.de>
 
 	* tree-ssa.c (insert_debug_temp_for_var_def): For {CLOBBER}

gcc/cfgrtl.c

@@ -543,7 +543,7 @@ update_bb_for_insn (basic_block bb)
 }
 
 
-/* Like active_insn_p, except keep the return value clobber around
+/* Like active_insn_p, except keep the return value use or clobber around
    even after reload.  */
 
 static bool
@@ -556,8 +556,12 @@ flow_active_insn_p (const rtx_insn *insn)
      programs that fail to return a value.  Its effect is to
      keep the return value from being live across the entire
      function.  If we allow it to be skipped, we introduce the
-     possibility for register lifetime confusion.  */
-  if (GET_CODE (PATTERN (insn)) == CLOBBER
+     possibility for register lifetime confusion.
+     Similarly, keep a USE of the function return value, otherwise
+     the USE is dropped and we could fail to thread jump if USE
+     appears on some paths and not on others, see PR90257.  */
+  if ((GET_CODE (PATTERN (insn)) == CLOBBER
+       || GET_CODE (PATTERN (insn)) == USE)
       && REG_P (XEXP (PATTERN (insn), 0))
       && REG_FUNCTION_VALUE_P (XEXP (PATTERN (insn), 0)))
     return true;

gcc/lra-spills.c

@@ -740,6 +740,7 @@ lra_final_code_change (void)
   int i, hard_regno;
   basic_block bb;
   rtx_insn *insn, *curr;
+  rtx set;
   int max_regno = max_reg_num ();
 
   for (i = FIRST_PSEUDO_REGISTER; i < max_regno; i++)
@@ -818,5 +819,19 @@ lra_final_code_change (void)
 	      }
 	  if (insn_change_p)
 	    lra_update_operator_dups (id);
+
+	  if ((set = single_set (insn)) != NULL
+	      && REG_P (SET_SRC (set)) && REG_P (SET_DEST (set))
+	      && REGNO (SET_SRC (set)) == REGNO (SET_DEST (set)))
+	    {
+	      /* Remove an useless move insn.  IRA can generate move
+		 insns involving pseudos.  It is better remove them
+		 earlier to speed up compiler a bit.  It is also
+		 better to do it here as they might not pass final RTL
+		 check in LRA, (e.g. insn moving a control register
+		 into itself).  */
+	      lra_invalidate_insn_data (insn);
+	      delete_insn (insn);
+	    }
 	}
 }