No need to zero the acceleration caches before use.

src/gravity_cache.h

@@ -127,12 +127,11 @@ static INLINE void gravity_cache_init(struct gravity_cache *c, int count) {
  * @param gcount The number of particles to read.
  * @param gcount_padded The number of particle to read padded to the next
  * multiple of the vector length.
- * @param zero_output Do we need to zero the output caches ?
  * @param shift A shift to apply to all the particles.
  */
 __attribute__((always_inline)) INLINE void gravity_cache_populate(
     struct gravity_cache *c, const struct gpart *restrict gparts, int gcount,
-    int gcount_padded, int zero_output, double shift[3]) {
+    int gcount_padded, double shift[3]) {
 
   /* Make the compiler understand we are in happy vectorization land */
   float *restrict x = c->x;
@@ -140,17 +139,11 @@ __attribute__((always_inline)) INLINE void gravity_cache_populate(
   float *restrict z = c->z;
   float *restrict m = c->m;
   float *restrict epsilon = c->epsilon;
-  float *restrict a_x = c->a_x;
-  float *restrict a_y = c->a_y;
-  float *restrict a_z = c->a_z;
   swift_align_information(x, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(y, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(z, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(epsilon, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(m, SWIFT_CACHE_ALIGNMENT);
-  swift_align_information(a_x, SWIFT_CACHE_ALIGNMENT);
-  swift_align_information(a_y, SWIFT_CACHE_ALIGNMENT);
-  swift_align_information(a_z, SWIFT_CACHE_ALIGNMENT);
   swift_assume_size(gcount_padded, VEC_SIZE);
 
   /* Fill the input caches */
@@ -174,13 +167,6 @@ __attribute__((always_inline)) INLINE void gravity_cache_populate(
     epsilon[i] = 0.f;
     m[i] = 0.f;
   }
-
-  /* Zero the output caches */
-  if (zero_output) {
-    bzero(a_x, gcount_padded * sizeof(float));
-    bzero(a_y, gcount_padded * sizeof(float));
-    bzero(a_z, gcount_padded * sizeof(float));
-  }
 }
 
 /**
@@ -191,11 +177,10 @@ __attribute__((always_inline)) INLINE void gravity_cache_populate(
  * @param gcount The number of particles to read.
  * @param gcount_padded The number of particle to read padded to the next
  * multiple of the vector length.
- * @param zero_output Do we need to zero the output caches ?
  */
 __attribute__((always_inline)) INLINE void gravity_cache_populate_no_shift(
     struct gravity_cache *c, const struct gpart *restrict gparts, int gcount,
-    int gcount_padded, int zero_output) {
+    int gcount_padded) {
 
   /* Make the compiler understand we are in happy vectorization land */
   float *restrict x = c->x;
@@ -203,17 +188,12 @@ __attribute__((always_inline)) INLINE void gravity_cache_populate_no_shift(
   float *restrict z = c->z;
   float *restrict m = c->m;
   float *restrict epsilon = c->epsilon;
-  float *restrict a_x = c->a_x;
-  float *restrict a_y = c->a_y;
-  float *restrict a_z = c->a_z;
   swift_align_information(x, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(y, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(z, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(epsilon, SWIFT_CACHE_ALIGNMENT);
   swift_align_information(m, SWIFT_CACHE_ALIGNMENT);
-  swift_align_information(a_x, SWIFT_CACHE_ALIGNMENT);
-  swift_align_information(a_y, SWIFT_CACHE_ALIGNMENT);
-  swift_align_information(a_z, SWIFT_CACHE_ALIGNMENT);
+  swift_assume_size(gcount_padded, VEC_SIZE);
 
   /* Fill the input caches */
   for (int i = 0; i < gcount; ++i) {
@@ -236,13 +216,6 @@ __attribute__((always_inline)) INLINE void gravity_cache_populate_no_shift(
     epsilon[i] = 0.f;
     m[i] = 0.f;
   }
-
-  /* Zero the output caches */
-  if (zero_output) {
-    bzero(a_x, gcount_padded * sizeof(float));
-    bzero(a_y, gcount_padded * sizeof(float));
-    bzero(a_z, gcount_padded * sizeof(float));
-  }
 }
 
 /**

src/runner_doiact_grav.h

@@ -188,10 +188,9 @@ void runner_dopair_grav_pp_full(struct runner *r, struct cell *ci,
   const int gcount_padded_j = gcount_j - (gcount_j % VEC_SIZE) + VEC_SIZE;
 
   /* Fill the caches */
-  gravity_cache_populate(ci_cache, gparts_i, gcount_i, gcount_padded_i,
-                         ci_active, shift);
-  gravity_cache_populate_no_shift(cj_cache, gparts_j, gcount_j, gcount_padded_j,
-                                  cj_active);
+  gravity_cache_populate(ci_cache, gparts_i, gcount_i, gcount_padded_i, shift);
+  gravity_cache_populate_no_shift(cj_cache, gparts_j, gcount_j,
+                                  gcount_padded_j);
 
   /* Ok... Here we go ! */
 
@@ -281,9 +280,9 @@ void runner_dopair_grav_pp_full(struct runner *r, struct cell *ci,
       }
 
       /* Store everything back in cache */
-      ci_cache->a_x[pid] += a_x;
-      ci_cache->a_y[pid] += a_y;
-      ci_cache->a_z[pid] += a_z;
+      ci_cache->a_x[pid] = a_x;
+      ci_cache->a_y[pid] = a_y;
+      ci_cache->a_z[pid] = a_z;
     }
   }
 
@@ -374,9 +373,9 @@ void runner_dopair_grav_pp_full(struct runner *r, struct cell *ci,
       }
 
       /* Store everything back in cache */
-      cj_cache->a_x[pjd] += a_x;
-      cj_cache->a_y[pjd] += a_y;
-      cj_cache->a_z[pjd] += a_z;
+      cj_cache->a_x[pjd] = a_x;
+      cj_cache->a_y[pjd] = a_y;
+      cj_cache->a_z[pjd] = a_z;
     }
   }
 
@@ -531,10 +530,9 @@ void runner_dopair_grav_pp_truncated(struct runner *r, struct cell *ci,
   const int gcount_padded_j = gcount_j - (gcount_j % VEC_SIZE) + VEC_SIZE;
 
   /* Fill the caches */
-  gravity_cache_populate(ci_cache, gparts_i, gcount_i, gcount_padded_i,
-                         ci_active, shift);
-  gravity_cache_populate_no_shift(cj_cache, gparts_j, gcount_j, gcount_padded_j,
-                                  cj_active);
+  gravity_cache_populate(ci_cache, gparts_i, gcount_i, gcount_padded_i, shift);
+  gravity_cache_populate_no_shift(cj_cache, gparts_j, gcount_j,
+                                  gcount_padded_j);
 
   /* Ok... Here we go ! */
 
@@ -629,9 +627,9 @@ void runner_dopair_grav_pp_truncated(struct runner *r, struct cell *ci,
       }
 
       /* Store everything back in cache */
-      ci_cache->a_x[pid] += a_x;
-      ci_cache->a_y[pid] += a_y;
-      ci_cache->a_z[pid] += a_z;
+      ci_cache->a_x[pid] = a_x;
+      ci_cache->a_y[pid] = a_y;
+      ci_cache->a_z[pid] = a_z;
     }
   }
 
@@ -727,9 +725,9 @@ void runner_dopair_grav_pp_truncated(struct runner *r, struct cell *ci,
       }
 
       /* Store everything back in cache */
-      cj_cache->a_x[pjd] += a_x;
-      cj_cache->a_y[pjd] += a_y;
-      cj_cache->a_z[pjd] += a_z;
+      cj_cache->a_x[pjd] = a_x;
+      cj_cache->a_y[pjd] = a_y;
+      cj_cache->a_z[pjd] = a_z;
     }
   }