[NDS32] Add new option -malways-save-lp.

gcc/
	* config/nds32/nds32.c (nds32_compute_stack_frame): Consider
	flag_always_save_lp condition.
	* config/nds32/nds32.opt (malways-save-lp): New option.

From-SVN: r259553

gcc/ChangeLog

+2018-04-22  Chung-Ju Wu  <jasonwucj@gmail.com>
+
+	* config/nds32/nds32.c (nds32_compute_stack_frame): Consider
+	flag_always_save_lp condition.
+	* config/nds32/nds32.opt (malways-save-lp): New option.
+
 2018-04-22  Shiva Chen  <shiva0217@gmail.com>
 
 	* config/nds32/nds32-protos.h (nds32_use_load_post_increment): Declare.

gcc/config/nds32/nds32.c

@@ -436,7 +436,8 @@ nds32_compute_stack_frame (void)
 
   /* If $lp value is required to be saved on stack, it needs 4 bytes space.
      Check whether $lp is ever live.  */
-  cfun->machine->lp_size = (df_regs_ever_live_p (LP_REGNUM)) ? 4 : 0;
+  cfun->machine->lp_size
+    = (flag_always_save_lp || df_regs_ever_live_p (LP_REGNUM)) ? 4 : 0;
 
   /* Initially there is no padding bytes.  */
   cfun->machine->callee_saved_area_gpr_padding_bytes = 0;

gcc/config/nds32/nds32.opt

@@ -321,6 +321,10 @@ mext-fpu-dp
 Target Report Mask(FPU_DOUBLE)
 Generate double-precision floating-point instructions.
 
+malways-save-lp
+Target Var(flag_always_save_lp) Init(0)
+Always save $lp in the stack.
+
 munaligned-access
 Target Report Var(flag_unaligned_access) Init(0)
 Enable unaligned word and halfword accesses to packed data.