Tweak SVE dot kernel

This changes the SVE dot kernel to only predicate when necessary as well
as streamlining the assembly a bit. The benchmarks seem to indicate this
can improve performance by ~33%.

Author: Mousius

kernel/arm64/dot_kernel_sve.c

@@ -1,4 +1,5 @@
 /***************************************************************************
+Copyright (c) 2023, The OpenBLAS Project
 Copyright (c) 2022, Arm Ltd
 All rights reserved.
 Redistribution and use in source and binary forms, with or without
@@ -30,37 +31,84 @@ THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <arm_sve.h>
 
 #ifdef DOUBLE
-#define SVE_TYPE svfloat64_t
-#define SVE_ZERO svdup_f64(0.0)
-#define SVE_WHILELT svwhilelt_b64
-#define SVE_ALL svptrue_b64()
-#define SVE_WIDTH svcntd()
+#define DTYPE "d"
+#define WIDTH "d"
+#define SHIFT "3"
 #else
-#define SVE_TYPE svfloat32_t
-#define SVE_ZERO svdup_f32(0.0)
-#define SVE_WHILELT svwhilelt_b32
-#define SVE_ALL svptrue_b32()
-#define SVE_WIDTH svcntw()
+#define DTYPE "s"
+#define WIDTH "w"
+#define SHIFT "2"
 #endif
 
-static FLOAT dot_kernel_sve(BLASLONG n, FLOAT *x, FLOAT *y) {
-        SVE_TYPE acc_a = SVE_ZERO;
-        SVE_TYPE acc_b = SVE_ZERO;
+#define COUNT \
+"        cnt"WIDTH"    x9                                   \n"
+#define SETUP_TRUE \
+"        ptrue   p0."DTYPE"                              \n"
+#define OFFSET_INPUTS                                     \
+"        add     x12, %[X_], x9, lsl #"SHIFT"               \n" \
+"        add     x13, %[Y_], x9, lsl #"SHIFT"               \n"
+#define TAIL_WHILE                                        \
+"        whilelo p1."DTYPE", x8, x0                         \n"
+#define UPDATE(pg, x,y,out)                               \
+"        ld1"WIDTH"    { z2."DTYPE" }, "pg"/z, ["x", x8, lsl #"SHIFT"]  \n" \
+"        ld1"WIDTH"    { z3."DTYPE" }, "pg"/z, ["y", x8, lsl #"SHIFT"]  \n" \
+"        fmla    "out"."DTYPE", "pg"/m, z2."DTYPE", z3."DTYPE"      \n"
+#define SUM_VECTOR(v) \
+"        faddv   "DTYPE""v", p0, z"v"."DTYPE"                     \n"
+#define RET \
+"        fadd    %"DTYPE"[RET_], "DTYPE"1, "DTYPE"0                     \n"
 
-        BLASLONG sve_width = SVE_WIDTH;
+#define DOT_KERNEL                                        \
+        COUNT                                             \
+"        mov     z1.d, #0                             \n" \
+"        mov     z0.d, #0                             \n" \
+"        mov     x8, #0                               \n" \
+"        movi    d1, #0x0                             \n" \
+        SETUP_TRUE                                        \
+"        neg     x10, x9, lsl #1                      \n" \
+"        ands    x11, x10, x0                         \n" \
+"        b.eq    .Lskip_2x                            \n" \
+        OFFSET_INPUTS                                     \
+".Lvector_2x:                                         \n" \
+        UPDATE("p0", "%[X_]", "%[Y_]", "z1") \
+        UPDATE("p0", "x12", "x13", "z0") \
+"        sub     x8, x8, x10                          \n" \
+"        cmp     x8, x11                              \n" \
+"        b.lo    .Lvector_2x                          \n" \
+        SUM_VECTOR("1") \
+".Lskip_2x:                                           \n" \
+"        neg     x10, x9                              \n" \
+"        and     x10, x10, x0                         \n" \
+"        cmp     x8, x10                              \n" \
+"        b.hs    .Ltail                               \n" \
+".Lvector_1x:                                         \n" \
+        UPDATE("p0", "%[X_]", "%[Y_]", "z0")              \
+"        add     x8, x8, x9                           \n" \
+"        cmp     x8, x10                              \n" \
+"        b.lo    .Lvector_1x                          \n" \
+".Ltail:                                              \n" \
+"        cmp     x10, x0                              \n" \
+"        b.eq    .Lend                                \n" \
+        TAIL_WHILE                                        \
+        UPDATE("p1", "%[X_]", "%[Y_]", "z0")              \
+".Lend:                                               \n" \
+        SUM_VECTOR("0") \
+        RET
 
-        for (BLASLONG i = 0; i < n; i += sve_width * 2) {
-                svbool_t pg_a = SVE_WHILELT((uint64_t)i, (uint64_t)n);
-                svbool_t pg_b = SVE_WHILELT((uint64_t)(i + sve_width), (uint64_t)n);
+static
+FLOAT
+dot_kernel_sve(BLASLONG n, FLOAT* x, FLOAT* y)
+{
+  FLOAT ret;
 
-                SVE_TYPE x_vec_a = svld1(pg_a, &x[i]);
-                SVE_TYPE y_vec_a = svld1(pg_a, &y[i]);
-                SVE_TYPE x_vec_b = svld1(pg_b, &x[i + sve_width]);
-                SVE_TYPE y_vec_b = svld1(pg_b, &y[i + sve_width]);
+  asm(DOT_KERNEL
+      :
+        [RET_] "=&w" (ret)
+      :
+        [N_] "r" (n),
+        [X_] "r" (x),
+        [Y_] "r" (y)
+      :);
 
-                acc_a = svmla_m(pg_a, acc_a, x_vec_a, y_vec_a);
-                acc_b = svmla_m(pg_b, acc_b, x_vec_b, y_vec_b);
-        }
-
-        return svaddv(SVE_ALL, acc_a) + svaddv(SVE_ALL, acc_b);
+  return ret;
 }