Set default sched pressure algorithm

The Arm backend sets the default sched-pressure algorithm to SCHED_PRESSURE_MODEL.
Benchmarking on AArch64 shows this speeds up floating point performance on SPEC -
eg. CactusBSSN improves by ~16%.  The gains are mostly due to less spilling,
so enable this on AArch64 by default.

    gcc/
	* config/aarch64/aarch64.c (aarch64_override_options_internal):
	Set PARAM_SCHED_PRESSURE_ALGORITHM to SCHED_PRESSURE_MODEL.

From-SVN: r254378

gcc/ChangeLog

+2017-11-03  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* config/aarch64/aarch64.c (aarch64_override_options_internal):
+	Set PARAM_SCHED_PRESSURE_ALGORITHM to SCHED_PRESSURE_MODEL.
+
 2017-11-03  Kito Cheng  <kito.cheng@gmail.com>
 
 	* config/riscv/riscv.c (riscv_legitimize_move): Handle

gcc/config/aarch64/aarch64.c

@@ -9110,6 +9110,11 @@ aarch64_override_options_internal (struct gcc_options *opts)
 			   opts->x_param_values,
 			   global_options_set.x_param_values);
 
+  /* Use the alternative scheduling-pressure algorithm by default.  */
+  maybe_set_param_value (PARAM_SCHED_PRESSURE_ALGORITHM, SCHED_PRESSURE_MODEL,
+			 opts->x_param_values,
+			 global_options_set.x_param_values);
+
   /* Enable sw prefetching at specified optimization level for
      CPUS that have prefetch.  Lower optimization level threshold by 1
      when profiling is enabled.  */