Optimize gemv_n_sve_v1x3 kernel

- Calculate predicate outside the loop
- Divide matrix in blocks of 3

CONTRIBUTORS.md

@@ -253,4 +253,7 @@ In chronological order:
   * [2025-02-27] Add sbgemv_n_neon kernel
 
 * Abhishek Kumar <https://github.com/abhishek-iitmadras>
-  * [2025-04-22] Optimise dot kernel for NEOVERSE V1
+  * [2025-04-22] Optimise dot kernel for NEOVERSE V1
+
+* Sharif Inamdar <sharif.inamdar@arm.com>
+  * [2025-06-05] Optimize gemv_n_sve_v1x3 kernel

kernel/arm64/gemv_n_sve_v1x3.c

@@ -52,17 +52,17 @@ int CNAME(BLASLONG m, BLASLONG n, BLASLONG dummy1, FLOAT alpha, FLOAT *a,
           BLASLONG lda, FLOAT *x, BLASLONG inc_x, FLOAT *y, BLASLONG inc_y,
           FLOAT *buffer)
 {
-  BLASLONG i;
-  BLASLONG ix,iy;
-  BLASLONG j;
-  FLOAT *a_ptr;
+  BLASLONG i, j;
+  BLASLONG ix = 0;
+  BLASLONG iy;
+  FLOAT *a_ptr = a;
   FLOAT temp;
 
-  ix = 0;
-  a_ptr = a;
-
   if (inc_y == 1) {
-    BLASLONG width = (n + 3 - 1) / 3;
+    BLASLONG width = n / 3; // Only process full 3-column blocks
+    BLASLONG sve_size = SV_COUNT();
+    svbool_t pg_full = SV_TRUE();
+    svbool_t pg_tail = SV_WHILE(0, m % sve_size);
 
     FLOAT *a0_ptr = a_ptr + lda * width * 0;
     FLOAT *a1_ptr = a_ptr + lda * width * 1;
@@ -73,57 +73,75 @@ int CNAME(BLASLONG m, BLASLONG n, BLASLONG dummy1, FLOAT alpha, FLOAT *a,
     FLOAT *x2_ptr = x + inc_x * width * 2;
 
     for (j = 0; j < width; j++) {
-      svbool_t pg00 = ((j + width * 0) < n) ? SV_TRUE() : svpfalse();
-      svbool_t pg01 = ((j + width * 1) < n) ? SV_TRUE() : svpfalse();
-      svbool_t pg02 = ((j + width * 2) < n) ? SV_TRUE() : svpfalse();
+      SV_TYPE temp0_vec = SV_DUP(alpha * x0_ptr[ix]);
+      SV_TYPE temp1_vec = SV_DUP(alpha * x1_ptr[ix]);
+      SV_TYPE temp2_vec = SV_DUP(alpha * x2_ptr[ix]);
 
-      SV_TYPE temp0_vec = ((j + width * 0) < n) ? SV_DUP(alpha * x0_ptr[ix]) : SV_DUP(0.0);
-      SV_TYPE temp1_vec = ((j + width * 1) < n) ? SV_DUP(alpha * x1_ptr[ix]) : SV_DUP(0.0);
-      SV_TYPE temp2_vec = ((j + width * 2) < n) ? SV_DUP(alpha * x2_ptr[ix]) : SV_DUP(0.0);
       i = 0;
-      BLASLONG sve_size = SV_COUNT();
-      while ((i + sve_size * 1 - 1) < m) {
-        SV_TYPE y0_vec = svld1_vnum(SV_TRUE(), y + i, 0);
+      while ((i + sve_size - 1) < m) {
+        SV_TYPE y0_vec = svld1(pg_full, y + i);
 
-        SV_TYPE a00_vec = svld1_vnum(pg00, a0_ptr + i, 0);
-        SV_TYPE a01_vec = svld1_vnum(pg01, a1_ptr + i, 0);
-        SV_TYPE a02_vec = svld1_vnum(pg02, a2_ptr + i, 0);
+        SV_TYPE a00_vec = svld1(pg_full, a0_ptr + i);
+        SV_TYPE a01_vec = svld1(pg_full, a1_ptr + i);
+        SV_TYPE a02_vec = svld1(pg_full, a2_ptr + i);
 
-        y0_vec = svmla_m(pg00, y0_vec, temp0_vec, a00_vec);
-        y0_vec = svmla_m(pg01, y0_vec, temp1_vec, a01_vec);
-        y0_vec = svmla_m(pg02, y0_vec, temp2_vec, a02_vec);
+        y0_vec = svmla_x(pg_full, y0_vec, temp0_vec, a00_vec);
+        y0_vec = svmla_x(pg_full, y0_vec, temp1_vec, a01_vec);
+        y0_vec = svmla_x(pg_full, y0_vec, temp2_vec, a02_vec);
 
-        svst1_vnum(SV_TRUE(), y + i, 0, y0_vec);
-        i += sve_size * 1;
+        svst1(pg_full, y + i, y0_vec);
+        i += sve_size;
       }
 
       if (i < m) {
-        svbool_t pg0 = SV_WHILE(i + sve_size * 0, m);
-
-        pg00 = svand_z(SV_TRUE(), pg0, pg00);
-        pg01 = svand_z(SV_TRUE(), pg0, pg01);
-        pg02 = svand_z(SV_TRUE(), pg0, pg02);
+        SV_TYPE y0_vec = svld1(pg_tail, y + i);
 
-        SV_TYPE y0_vec = svld1_vnum(pg0, y + i, 0);
+        SV_TYPE a00_vec = svld1(pg_tail, a0_ptr + i);
+        SV_TYPE a01_vec = svld1(pg_tail, a1_ptr + i);
+        SV_TYPE a02_vec = svld1(pg_tail, a2_ptr + i);
 
-        SV_TYPE a00_vec = svld1_vnum(pg00, a0_ptr + i, 0);
-        SV_TYPE a01_vec = svld1_vnum(pg01, a1_ptr + i, 0);
-        SV_TYPE a02_vec = svld1_vnum(pg02, a2_ptr + i, 0);
+        y0_vec = svmla_m(pg_tail, y0_vec, temp0_vec, a00_vec);
+        y0_vec = svmla_m(pg_tail, y0_vec, temp1_vec, a01_vec);
+        y0_vec = svmla_m(pg_tail, y0_vec, temp2_vec, a02_vec);
 
-        y0_vec = svmla_m(pg00, y0_vec, temp0_vec, a00_vec);
-        y0_vec = svmla_m(pg01, y0_vec, temp1_vec, a01_vec);
-        y0_vec = svmla_m(pg02, y0_vec, temp2_vec, a02_vec);
-
-        svst1_vnum(pg0, y + i, 0, y0_vec);
+        svst1(pg_tail, y + i, y0_vec);
       }
       a0_ptr += lda;
       a1_ptr += lda;
       a2_ptr += lda;
       ix += inc_x;
     }
+    // Handle remaining n % 3 columns
+    for (j = width * 3; j < n; j++) {
+      FLOAT *a_col = a + j * lda;
+      temp = alpha * x[j * inc_x];
+      SV_TYPE temp_vec = SV_DUP(temp);
+
+      i = 0;
+      while ((i + sve_size - 1) < m) {
+        SV_TYPE y_vec = svld1(pg_full, y + i);
+
+        SV_TYPE a_vec = svld1(pg_full, a_col + i);
+
+        y_vec = svmla_x(pg_full, y_vec, temp_vec, a_vec);
+
+        svst1(pg_full, y + i, y_vec);
+        i += sve_size;
+      }
+      if (i < m) {
+        SV_TYPE y_vec = svld1(pg_tail, y + i);
+
+        SV_TYPE a_vec = svld1(pg_tail, a_col + i);
+
+        y_vec = svmla_m(pg_tail, y_vec, temp_vec, a_vec);
+
+        svst1(pg_tail, y + i, y_vec);
+      }
+    }
     return(0);
   }
 
+  // Fallback scalar loop
   for (j = 0; j < n; j++) {
     temp = alpha * x[ix];
     iy = 0;