[PATCH 4/5]AArch64 sve: optimize add reduction patterns

Tamar Christina tamar.christina@arm.com
Tue Aug 31 13:35:47 GMT 2021


Hi All,

The following loop does a conditional reduction using an add:

#include <stdint.h>

int32_t f (int32_t *restrict array, int len, int min)
{
  int32_t iSum = 0;

  for (int i=0; i<len; i++) {
    if (array[i] >= min)
       iSum += array[i];
  }
  return iSum;
}

for this we currently generate:

        mov     z1.b, #0
        mov     z2.s, w2
        mov     z3.d, z1.d
        ptrue   p2.b, all
        ld1w    z0.s, p0/z, [x0, x3, lsl 2]
        cmpge   p1.s, p2/z, z0.s, z2.s
        add     x3, x3, x4
        sel     z0.s, p1, z0.s, z3.s
        add     z1.s, p0/m, z1.s, z0.s
        whilelo p0.s, w3, w1

where the SEL is unneeded as it's selecting between 0 or a value.  This can be
optimized to just doing the conditional add on p1 instead of p0.  After this
patch we generate:

        mov     z2.s, w2
        mov     z0.b, #0
        ptrue   p1.b, all
        ld1w    z1.s, p0/z, [x0, x3, lsl 2]
        cmpge   p0.s, p0/z, z1.s, z2.s
        add     x3, x3, x4
        add     z0.s, p0/m, z0.s, z1.s
        whilelo p0.s, w3, w1

and so we drop the SEL and the 0 move.

Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

	* match.pd: New rule.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/pred-cond-reduc.c: New test.

--- inline copy of patch -- 
diff --git a/gcc/match.pd b/gcc/match.pd
index 19cbad7592787a568d4a7cfd62746d5844c0be5f..ec98a302ac773647413f776fba15930ad247c747 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -6978,6 +6978,18 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
         && element_precision (type) == element_precision (op_type))
     (view_convert (cond_op @2 @3 @4 @5 (view_convert:op_type @1)))))))
 
+/* Detect simplication for a conditional reduction where
+
+   a = mask1 ? b : 0
+   c = mask2 ? d + a : d
+
+   is turned into
+
+   c = mask1 && mask2 ? d + b : d.  */
+(simplify
+  (IFN_COND_ADD @0 @1 (vec_cond @2 @3 integer_zerop) @1)
+   (IFN_COND_ADD (bit_and @0 @2) @1 @3 @1))
+
 /* For pointers @0 and @2 and nonnegative constant offset @1, look for
    expressions like:
 
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/pred-cond-reduc.c b/gcc/testsuite/gcc.target/aarch64/sve/pred-cond-reduc.c
new file mode 100644
index 0000000000000000000000000000000000000000..bd53025d3f17224004244dadc88e0c68ded23f12
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/sve/pred-cond-reduc.c
@@ -0,0 +1,18 @@
+/* { dg-do assemble { target aarch64_asm_sve_ok } } */
+/* { dg-options "-O3 --save-temps" } */
+
+#include <stdint.h>
+
+int32_t f (int32_t *restrict array, int len, int min)
+{
+  int32_t iSum = 0;
+
+  for (int i=0; i<len; i++) {
+    if (array[i] >= min)
+       iSum += array[i];
+  }
+  return iSum;
+}
+
+
+/* { dg-final { scan-assembler-not {\tsel\tz[0-9]+\.s, p1, z[0-9]+\.s, z[0-9]+\.s} } } */


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