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Re: [RFC] [PATCH, i386] Adjust unroll factor for bdver3 and bdver4


On Wed, Nov 20, 2013 at 7:26 PM, Gopalasubramanian, Ganesh
<Ganesh.Gopalasubramanian@amd.com> wrote:

> Steamroller processors contain a loop predictor and a loop buffer, which may make unrolling small loops less important.
> When unrolling small loops for steamroller, making the unrolled loop fit in the loop buffer should be a priority.
>
> This patch uses a heuristic approach (number of memory references) to decide the unrolling factor for small loops.
> This patch has some noise in SPEC 2006 results.
>
> Bootstrapping passes.
>
> I would like to know your comments before committing.

Please split the patch to target-dependant and target-independant
part, and get target-idependant part reviewed first.

This part:

+  if (ix86_tune != PROCESSOR_BDVER3 && ix86_tune != PROCESSOR_BDVER4)
+  {
+    return nunroll;
+  }

is wrong. You should introduce tune variable (as H.J. suggested) and
check that variable here. Target dependant tuning options should be in
x86-tune.def, so everything regarding tuning can be found in one
place.

+        if (INSN_P (insn) && INSN_CODE (insn) != -1)
+            for_each_rtx (&insn, (rtx_function) ix86_loop_memcount,
&mem_count);

if (NONDEBUG_INSN_P (insn))
  for_each_rtx (&PATTERN(insn), ...);

otherwise your heuristics will depend on -g compile option.

+  if ( (mem_count*nunroll) <= 32)

Extra parenthesis.

+static int
+ix86_loop_memcount (rtx *x, unsigned *mem_count)
+{
+  if (*x != NULL_RTX && MEM_P (*x))

*x will never be null for active insns.

Uros.


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