[LRA]: Implement output stack pointer reloads

LRA prohibited output stack pointer reloads but it resulted in LRA
failure for AVR target which has no arithmetic insns working with the
stack pointer register.  Given patch implements the output stack
pointer reloads.

gcc/ChangeLog:

	* lra-constraints.cc (goal_alt_out_sp_reload_p): New flag.
	(process_alt_operands): Set the flag.
	(curr_insn_transform): Modify stack pointer offsets if output
	stack pointer reload is generated.

1 files changed, 32 insertions, 6 deletions

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index 09ff6de..2623990 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -1466,6 +1466,8 @@ static int goal_alt_dont_inherit_ops[MAX_RECOG_OPERANDS];
 static bool goal_alt_swapped;
 /* The chosen insn alternative.	 */
 static int goal_alt_number;
+/* True if output reload of the stack pointer should be generated.  */
+static bool goal_alt_out_sp_reload_p;
 
 /* True if the corresponding operand is the result of an equivalence
    substitution.  */
@@ -2128,6 +2130,9 @@ process_alt_operands (int only_alternative)
   int curr_alt_dont_inherit_ops_num;
   /* Numbers of operands whose reload pseudos should not be inherited.	*/
   int curr_alt_dont_inherit_ops[MAX_RECOG_OPERANDS];
+  /* True if output stack pointer reload should be generated for the current
+     alternative.  */
+  bool curr_alt_out_sp_reload_p;
   rtx op;
   /* The register when the operand is a subreg of register, otherwise the
      operand itself.  */
@@ -2211,7 +2216,8 @@ process_alt_operands (int only_alternative)
 	}
       reject += static_reject;
       early_clobbered_regs_num = 0;
-
+      curr_alt_out_sp_reload_p = false;
+      
       for (nop = 0; nop < n_operands; nop++)
 	{
 	  const char *p;
@@ -2682,12 +2688,10 @@ process_alt_operands (int only_alternative)
 	      bool no_regs_p;
 
 	      reject += op_reject;
-	      /* Never do output reload of stack pointer.  It makes
-		 impossible to do elimination when SP is changed in
-		 RTL.  */
-	      if (op == stack_pointer_rtx && ! frame_pointer_needed
+	      /* Mark output reload of the stack pointer.  */
+	      if (op == stack_pointer_rtx
 		  && curr_static_id->operand[nop].type != OP_IN)
-		goto fail;
+		curr_alt_out_sp_reload_p = true;
 
 	      /* If this alternative asks for a specific reg class, see if there
 		 is at least one allocatable register in that class.  */
@@ -3317,6 +3321,7 @@ process_alt_operands (int only_alternative)
 	  for (nop = 0; nop < curr_alt_dont_inherit_ops_num; nop++)
 	    goal_alt_dont_inherit_ops[nop] = curr_alt_dont_inherit_ops[nop];
 	  goal_alt_swapped = curr_swapped;
+	  goal_alt_out_sp_reload_p = curr_alt_out_sp_reload_p;
 	  best_overall = overall;
 	  best_losers = losers;
 	  best_reload_nregs = reload_nregs;
@@ -4836,6 +4841,27 @@ curr_insn_transform (bool check_only_p)
 	lra_asm_insn_error (curr_insn);
     }
   lra_process_new_insns (curr_insn, before, after, "Inserting insn reload");
+  if (goal_alt_out_sp_reload_p)
+    {
+      /* We have an output stack pointer reload -- update sp offset: */
+      rtx set;
+      bool done_p = false;
+      poly_int64 sp_offset = curr_id->sp_offset;
+      for (rtx_insn *insn = after; insn != NULL_RTX; insn = NEXT_INSN (insn))
+	if ((set = single_set (insn)) != NULL_RTX
+	    && SET_DEST (set) == stack_pointer_rtx)
+	  {
+	    lra_assert (!done_p);
+	    curr_id->sp_offset = 0;
+	    lra_insn_recog_data_t id = lra_get_insn_recog_data (insn);
+	    id->sp_offset = sp_offset;
+	    if (lra_dump_file != NULL)
+	      fprintf (lra_dump_file,
+		       "            Moving sp offset from insn %u to %u\n",
+		       INSN_UID (curr_insn), INSN_UID (insn));
+	  }
+      lra_assert (!done_p);
+    }
   return change_p;
 }