vulkan: improve im2col (ggml-org#11826)

* vulkan: improve im2col performance

Author: daniandtheweb

ggml/src/ggml-vulkan/vulkan-shaders/im2col.comp

@@ -40,6 +40,20 @@ void main() {
     const uint batch = gl_GlobalInvocationID.z / p.IC;
     const uint ic = gl_GlobalInvocationID.z % p.IC;
 
+    const uint src_base = ic * p.offset_delta + batch * p.batch_offset;
+    const uint dst_base = ((batch * p.OH + oh) * p.OW) * p.CHW + ic * (p.KW * p.KH);
+    const int oh_s1 = int(oh) * p.s1;
+    const uint ksize = p.OW * (p.KH > 1 ? p.KW : 1);
+
+    const uint base_linear_idx = gidx * NUM_ITER;
+
+    const uint max_ky = ksize / p.OW;
+
+    uint current_kx = base_linear_idx / ksize;
+    const uint rem = base_linear_idx - (current_kx * ksize);
+    uint current_ky = rem / p.OW;
+    uint current_ix = rem % p.OW;
+
     A_TYPE values[NUM_ITER];
     uint offset_dst[NUM_ITER];
     [[unroll]] for (uint idx = 0; idx < NUM_ITER; ++idx) {
@@ -48,36 +62,35 @@ void main() {
 
     [[unroll]] for (uint idx = 0; idx < NUM_ITER; ++idx) {
 
-        const uint i = gidx * NUM_ITER + idx;
+        const uint linear_idx = base_linear_idx + idx;
 
-        const uint ksize = p.OW * (p.KH > 1 ? p.KW : 1);
-        const uint kx = i / ksize;
-        const uint kd = kx * ksize;
-        const uint ky = (i - kd) / p.OW;
-        const uint ix = i % p.OW;
+        if (linear_idx >= p.pelements) {
+            continue;
+        }
 
-        const uint iiw = ix * p.s0 + kx * p.d0 - p.p0;
-        const uint iih = oh * p.s1 + ky * p.d1 - p.p1;
+        const uint iiw = current_ix * p.s0 + current_kx * p.d0 - p.p0;
+        const uint iih = oh_s1 + current_ky * p.d1 - p.p1;
 
-        offset_dst[idx] =
-            ((batch * p.OH + oh) * p.OW + ix) * p.CHW +
-            (ic * (p.KW * p.KH) + ky * p.KW + kx);
+        offset_dst[idx] = dst_base + current_ix * p.CHW + current_ky * p.KW + current_kx;
 
-        if (i >= p.pelements) {
-            continue;
+        if ((iih < p.IH) && (iiw < p.IW)) {
+            values[idx] = data_a[src_base + iih * p.IW + iiw];
         }
 
-        if (iih < p.IH && iiw < p.IW) {
-            const uint offset_src = ic * p.offset_delta + batch * p.batch_offset;
-            values[idx] = data_a[offset_src + iih * p.IW + iiw];
+        if (++current_ix == p.OW) {
+            current_ix = 0;
+            if (++current_ky == max_ky) {
+                current_ky = 0;
+                current_kx++;
+            }
         }
     }
 
     [[unroll]] for (uint idx = 0; idx < NUM_ITER; ++idx) {
 
-        const uint i = gidx * NUM_ITER + idx;
+        const uint linear_idx = base_linear_idx + idx;
 
-        if (i >= p.pelements) {
+        if (linear_idx >= p.pelements) {
             continue;
         }