s390: Add -munroll-only-small-loops.

Inspired by Power we also introduce -munroll-only-small-loops.  This
implies activating -funroll-loops and -munroll-only-small-loops at -O2 and
above.

gcc/ChangeLog:

	* common/config/s390/s390-common.cc: Enable -funroll-loops and
	-munroll-only-small-loops for OPT_LEVELS_2_PLUS_SPEED_ONLY.
	* config/s390/s390.cc (s390_loop_unroll_adjust): Do not unroll
	loops larger than 12 instructions.
	(s390_override_options_after_change): Set unroll options.
	(s390_option_override_internal): Likewise.
	* config/s390/s390.opt: Document munroll-only-small-loops.

gcc/testsuite/ChangeLog:

	* gcc.target/s390/vector/vec-copysign.c: Do not unroll.
	* gcc.target/s390/zvector/autovec-double-quiet-uneq.c: Dito.
	* gcc.target/s390/zvector/autovec-double-signaling-ltgt.c: Dito.
	* gcc.target/s390/zvector/autovec-float-quiet-uneq.c: Dito.
	* gcc.target/s390/zvector/autovec-float-signaling-ltgt.c: Dito.

2 files changed, 35 insertions, 0 deletions

diff --git a/gcc/config/s390/s390.cc b/gcc/config/s390/s390.cc
index 5e06bf9..942ed26 100644
--- a/gcc/config/s390/s390.cc
+++ b/gcc/config/s390/s390.cc
@@ -15420,6 +15420,21 @@ s390_loop_unroll_adjust (unsigned nunroll, struct loop *loop)
   if (s390_tune < PROCESSOR_2097_Z10)
     return nunroll;
 
+  if (unroll_only_small_loops)
+    {
+      /* Only unroll loops smaller than or equal to 12 insns.  */
+      const unsigned int small_threshold = 12;
+
+      if (loop->ninsns > small_threshold)
+	return 0;
+
+      /* ???: Make this dependent on the type of registers in
+	 the loop.  Increase the limit for vector registers.  */
+      const unsigned int max_insns = optimize >= 3 ? 36 : 24;
+
+      nunroll = MIN (nunroll, max_insns / loop->ninsns);
+    }
+
   /* Count the number of memory references within the loop body.  */
   bbs = get_loop_body (loop);
   subrtx_iterator::array_type array;
@@ -15494,6 +15509,19 @@ static void
 s390_override_options_after_change (void)
 {
   s390_default_align (&global_options);
+
+  /* Explicit -funroll-loops turns -munroll-only-small-loops off.  */
+  if ((OPTION_SET_P (flag_unroll_loops) && flag_unroll_loops)
+       || (OPTION_SET_P (flag_unroll_all_loops)
+	   && flag_unroll_all_loops))
+    {
+      if (!OPTION_SET_P (unroll_only_small_loops))
+	unroll_only_small_loops = 0;
+      if (!OPTION_SET_P (flag_cunroll_grow_size))
+	flag_cunroll_grow_size = 1;
+    }
+  else if (!OPTION_SET_P (flag_cunroll_grow_size))
+    flag_cunroll_grow_size = flag_peel_loops || optimize >= 3;
 }
 
 static void
@@ -15703,6 +15731,9 @@ s390_option_override_internal (struct gcc_options *opts,
   /* Set the default alignment.  */
   s390_default_align (opts);
 
+  /* Set unroll options.  */
+  s390_override_options_after_change ();
+
   /* Call target specific restore function to do post-init work.  At the moment,
      this just sets opts->x_s390_cost_pointer.  */
   s390_function_specific_restore (opts, opts_set, NULL);
diff --git a/gcc/config/s390/s390.opt b/gcc/config/s390/s390.opt
index 9e8d3bf..c375b9c 100644
--- a/gcc/config/s390/s390.opt
+++ b/gcc/config/s390/s390.opt
@@ -321,3 +321,7 @@ and the default behavior is to emit separate multiplication and addition
 instructions for long doubles in vector registers, because measurements show
 that this improves performance.  This option allows overriding it for testing
 purposes.
+
+munroll-only-small-loops
+Target Undocumented Var(unroll_only_small_loops) Init(0) Save
+; Use conservative small loop unrolling.