Re: [ARM] Use vector wide add for mixed-mode adds

[Kyrill Tkachov]

Hi Michael,

On 23/09/15 00:52, Michael Collison wrote:

This is a modified version of the previous patch that removes the
documentation and read-md.c fixes. These patches have been submitted
separately and approved.

This patch is designed to address code that was not being vectorized due
to missing widening patterns in the ARM backend. Code such as:

int t6(int len, void * dummy, short * __restrict x)
{
    len = len & ~31;
    int result = 0;
    __asm volatile ("");
    for (int i = 0; i < len; i++)
      result += x[i];
    return result;
}

Validated on arm-none-eabi, arm-none-linux-gnueabi,
arm-none-linux-gnueabihf, and armeb-none-linux-gnueabihf.

2015-09-22  Michael Collison  <michael.colli...@linaro.org>

      * config/arm/neon.md (widen_<us>sum<mode>): New patterns
      where mode is VQI to improve mixed mode add vectorization.

Please list all the new define_expands and define_insns
in the changelog. Also, please add an ChangeLog entry for
the testsuite additions.

The approach looks ok to me with a few comments on some
parts of the patch itself.


+(define_insn "vec_sel_widen_ssum_hi<VQI:mode><VW:mode>3"
+  [(set (match_operand:<VW:V_widen> 0 "s_register_operand" "=w")
+       (plus:<VW:V_widen> (sign_extend:<VW:V_widen> (vec_select:VW (match_operand:VQI 1 
"s_register_operand" "%w")
+                                                  (match_operand:VQI 2 
"vect_par_constant_high" "")))
+                       (match_operand:<VW:V_widen> 3 "s_register_operand" 
"0")))]
+  "TARGET_NEON"
+  "vaddw.<V_s_elem>\t%q0, %q3, %f1"
+  [(set_attr "type" "neon_add_widen")
+  (set_attr "length" "8")]
+)


This is a single instruction, and it has a length of 4, so no need to override 
the length attribute.
Same with the other define_insns in this patch.


diff --git a/gcc/testsuite/gcc.target/arm/neon-vaddws16.c 
b/gcc/testsuite/gcc.target/arm/neon-vaddws16.c
new file mode 100644
index 0000000..ed10669
--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/neon-vaddws16.c
@@ -0,0 +1,21 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target arm_neon_hw } */

The arm_neon_hw check is usually used when you want to run the tests.
Since this is a compile-only tests you just need arm_neon_ok.

 +/* { dg-add-options arm_neon_ok } */
+/* { dg-options "-O3" } */
+
+
+int
+t6(int len, void * dummy, short * __restrict x)
+{
+  len = len & ~31;
+  int result = 0;
+  __asm volatile ("");
+  for (int i = 0; i < len; i++)
+    result += x[i];
+  return result;
+}
+
+/* { dg-final { scan-assembler "vaddw\.s16" } } */
+
+
+

Stray trailing newlines. Similar comments for the other testcases.

Thanks,
Kyrill