[PATCH][AArch64][2/2] Add sve_width -moverride tunable

[Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>]

Hi all,

On top of the previous patch that implements TARGET_ESTIMATED_POLY_VALUE
and adds an sve_width tuning field to the CPU structs, this patch implements
an -moverride knob to adjust this sve_width field to allow for experimentation.
Again, reminder that this only has an effect when compiling for VLA-SVE that is,
without msve-vector-bits=<foo>. This just adjusts tuning heuristics in the compiler,,
like profitability thresholds for vectorised versioned loops, and others.

It can be used, for example like -moverride=sve_width=256 to set the sve_width
tuning field to 256. Widths outside of the accepted SVE widths [128 - 2048] are rejected
as you'd expect.

Bootstrapped and tested on aarch64-none-linux-gnu.

Ok for trunk?

Thanks,
Kyrill

2018-12-07  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

    * config/aarch64/aarch64.c (aarch64_tuning_override_functions): Add
    sve_width entry.
    (aarch64_parse_sve_width_string): Define.

2018-12-07  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

    * gcc.target/aarch64/sve/override_sve_width_1.c: New test.

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 7ccc6b78d5872d6b43491badbfa9f2d70580015c..bad687d33479f4b6f8cbeaca799824e29b8e9ed1 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -1086,12 +1086,14 @@ struct aarch64_tuning_override_function
 
 static void aarch64_parse_fuse_string (const char*, struct tune_params*);
 static void aarch64_parse_tune_string (const char*, struct tune_params*);
+static void aarch64_parse_sve_width_string (const char*, struct tune_params*);
 
 static const struct aarch64_tuning_override_function
 aarch64_tuning_override_functions[] =
 {
   { "fuse", aarch64_parse_fuse_string },
   { "tune", aarch64_parse_tune_string },
+  { "sve_width", aarch64_parse_sve_width_string },
   { NULL, NULL }
 };
 
@@ -10834,6 +10836,34 @@ aarch64_parse_tune_string (const char *tune_string,
 				     "tune=");
 }
 
+/* Parse the sve_width tuning moverride string in TUNE_STRING.
+   Accept the valid SVE vector widths allowed by
+   aarch64_sve_vector_bits_enum and use it to override sve_width
+   in TUNE.  */
+
+static void
+aarch64_parse_sve_width_string (const char *tune_string,
+				struct tune_params *tune)
+{
+  int width = -1;
+
+  int n = sscanf (tune_string, "%d", &width);
+  if (n == EOF)
+    error ("invalid format for sve_width");
+  switch (width)
+    {
+      case SVE_128:
+      case SVE_256:
+      case SVE_512:
+      case SVE_1024:
+      case SVE_2048:
+	break;
+      default:
+	error ("invalid sve_width value: %d", width);
+    }
+  tune->sve_width = (enum aarch64_sve_vector_bits_enum) width;
+}
+
 /* Parse TOKEN, which has length LENGTH to see if it is a tuning option
    we understand.  If it is, extract the option string and handoff to
    the appropriate function.  */
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/override_sve_width_1.c b/gcc/testsuite/gcc.target/aarch64/sve/override_sve_width_1.c
new file mode 100644
index 0000000000000000000000000000000000000000..3752fdc2a7198783d2ed5c5f502c3227f98029b8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/override_sve_width_1.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 -moverride=sve_width=512" } */
+
+void __attribute__((noinline, noclone))
+vadd (int *dst, int *op1, int *op2, int count)
+{
+  for (int i = 0; i < count; ++i)
+    dst[i] = op1[i] + op2[i];
+}