regcprop.c (maybe_mode_change): Avoid creating copies of the stack pointer.

	* regcprop.c (maybe_mode_change): Avoid creating copies of the
	stack pointer.

	Revert:
	2017-04-13  Jeff Law  <law@redhat.com>
	* config/mips.mips.md (zero_extendsidi2): Do not allow SP to appear
	in operands[1] if it is a MEM and TARGET_MIPS16 is active.

From-SVN: r246970

gcc/ChangeLog

+2017-04-18  Jeff Law  <law@redhat.com>
+
+	* regcprop.c (maybe_mode_change): Avoid creating copies of the
+	stack pointer.
+
+	Revert:
+	2017-04-13  Jeff Law  <law@redhat.com>
+	* config/mips.mips.md (zero_extendsidi2): Do not allow SP to appear
+	in operands[1] if it is a MEM and TARGET_MIPS16 is active.
+
 2017-04-18  Georg-Johann Lay  <avr@gjlay.de>
 
 	PR target/79453

gcc/config/mips/mips.md

@@ -3493,10 +3493,7 @@
 (define_insn_and_split "*zero_extendsidi2"
   [(set (match_operand:DI 0 "register_operand" "=d,d")
         (zero_extend:DI (match_operand:SI 1 "nonimmediate_operand" "d,W")))]
-  "TARGET_64BIT && !ISA_HAS_EXT_INS
-   && !(TARGET_MIPS16
-        && MEM_P (operands[1])
-        && reg_mentioned_p (stack_pointer_rtx, operands[1]))"
+  "TARGET_64BIT && !ISA_HAS_EXT_INS"
   "@
    #
    lwu\t%0,%1"
@@ -3512,10 +3509,7 @@
 (define_insn "*zero_extendsidi2_dext"
   [(set (match_operand:DI 0 "register_operand" "=d,d")
         (zero_extend:DI (match_operand:SI 1 "nonimmediate_operand" "d,W")))]
-  "TARGET_64BIT && ISA_HAS_EXT_INS
-   && !(TARGET_MIPS16
-        && MEM_P (operands[1])
-        && reg_mentioned_p (stack_pointer_rtx, operands[1]))"
+  "TARGET_64BIT && ISA_HAS_EXT_INS"
   "@
    dext\t%0,%1,0,32
    lwu\t%0,%1"

gcc/regcprop.c

@@ -396,6 +396,13 @@ maybe_mode_change (machine_mode orig_mode, machine_mode copy_mode,
       && GET_MODE_SIZE (copy_mode) < GET_MODE_SIZE (new_mode))
     return NULL_RTX;
 
+  /* Avoid creating multiple copies of the stack pointer.  Some ports
+     assume there is one and only one stack pointer.
+
+     It's unclear if we need to do the same for other special registers.  */
+  if (regno == STACK_POINTER_REGNUM)
+    return NULL_RTX;
+
   if (orig_mode == new_mode)
     return gen_raw_REG (new_mode, regno);
   else if (mode_change_ok (orig_mode, new_mode, regno))