Fix Gemma3 image: ensure A matrix is packed, preallocate

Also ignore -2 tokens

PiperOrigin-RevId: 838869988

gemma/activations.h

@@ -66,6 +66,9 @@ struct AttentionActivations {
                            ? batch_size * layer_config.heads * 3
                            : batch_size * layer_config.heads,
                        allocator)),
+        vit_Q(MatFactory("Q2", batch_size, layer_config.qkv_dim, allocator)),
+        vit_K(MatFactory("K2", seq_len, layer_config.qkv_dim, allocator)),
+        vit_C(MatFactory("C2", batch_size, seq_len, allocator)),
         pre_att_rms_out(MatFactory("pre_att_rms_out", batch_size,
                                    config.model_dim, allocator)),
         att(MatFactory("att", batch_size, layer_config.heads * seq_len,
@@ -101,6 +104,7 @@ struct AttentionActivations {
     q.AllocateAndAttachRowPtrs(row_ptrs);
     q_bf.AllocateAndAttachRowPtrs(row_ptrs);
     q_T.AllocateAndAttachRowPtrs(row_ptrs);
+    vit_C.AllocateAndAttachRowPtrs(row_ptrs);
     att_sums.AllocateAndAttachRowPtrs(row_ptrs);
   }
 
@@ -109,6 +113,10 @@ struct AttentionActivations {
     q_bf.OverrideRows(batch_size);
     // q_T rows are always qkv_dim!
 
+    vit_Q.OverrideRows(batch_size);
+    // vit_K stays seq_len!
+    vit_C.OverrideRows(batch_size);
+
     pre_att_rms_out.OverrideRows(batch_size);
     att.OverrideRows(batch_size);
     att_out.OverrideRows(batch_size);
@@ -123,6 +131,10 @@ struct AttentionActivations {
   MatStorageT<BF16> q_bf;
   MatStorageT<BF16> q_T;  // Transposed to maximize attention speed.
 
+  MatStorageT<float> vit_Q;
+  MatStorageT<float> vit_K;
+  MatStorageT<float> vit_C;
+
   MatStorageT<float> pre_att_rms_out;
   MatStorageT<float> att;      // attention vector
   MatStorageT<float> att_out;  // attention output
@@ -150,6 +162,9 @@ struct AttentionActivationsPtrs {
     q = activations.q;
     q_bf = activations.q_bf;
     q_T = activations.q_T;
+    vit_Q = activations.vit_Q;
+    vit_K = activations.vit_K;
+    vit_C = activations.vit_C;
     pre_att_rms_out = activations.pre_att_rms_out;
     att = activations.att;
     att_out = activations.att_out;
@@ -164,6 +179,11 @@ struct AttentionActivationsPtrs {
     q.OverrideRows(batch_size);
     q_bf.OverrideRows(batch_size);
     // q_T rows are always qkv_dim!
+
+    vit_Q.OverrideRows(batch_size);
+    // vit_K stays seq_len!
+    vit_C.OverrideRows(batch_size);
+
     pre_att_rms_out.OverrideRows(batch_size);
     att.OverrideRows(batch_size);
     att_out.OverrideRows(batch_size);
@@ -184,6 +204,11 @@ struct AttentionActivationsPtrs {
   MatPtrT<BF16> q_bf;
   // Transposed query matrix for faster Q*K^T.
   MatPtrT<BF16> q_T;
+
+  MatPtrT<float> vit_Q;
+  MatPtrT<float> vit_K;
+  MatPtrT<float> vit_C;
+
   // Output of RMSNorm before attention, size batch_size x model_dim.
   MatPtrT<float> pre_att_rms_out;
   // Attention scores computed from Q*K^T, size batch_size x (q_heads *

gemma/run.cc

@@ -129,11 +129,15 @@ void ReplGemma(const ThreadingArgs& threading, const InferenceArgs& inference,
   // callback function invoked for each generated token.
   auto batch_stream_token = [&](size_t query_idx, size_t pos, int token,
                                 float) {
-    std::string token_text;
-    HWY_ASSERT(gemma.Tokenizer().Decode(std::vector<int>{token}, &token_text));
-
     HWY_ASSERT(pos == abs_pos);
     ++abs_pos;
+
+    std::string token_text;
+    if (!gemma.Tokenizer().Decode(std::vector<int>{token}, &token_text)) {
+      if (token == -2) return true;  // Gemma 3 ViT?
+      HWY_WARN("Failed to decode token %d.", token);
+    }
+
     const bool in_prompt = tokens_generated_this_turn < prompt_size;
     const bool first_response_token = tokens_generated_this_turn == prompt_size;
     ++tokens_generated_this_turn;

gemma/vit.cc

@@ -78,13 +78,9 @@ class VitAttention {
     const float query_scale = 1.0f / sqrtf(static_cast<float>(qkv_dim));
     PROFILER_ZONE("Gen.VitAttention.DotSoftmax");
 
-    // Shift Q, K, VT to MatStorageT.
-    MatStorageT<float> Q("Q2", Extents2D(num_tokens_, qkv_dim),
-                         env_.ctx.allocator, MatPadding::kPacked);
-    MatStorageT<float> K("K2", Extents2D(seq_len, qkv_dim), env_.ctx.allocator,
-                         MatPadding::kPacked);
-    MatStorageT<float> C("C2", Extents2D(num_tokens_, seq_len),
-                         env_.ctx.allocator, MatPadding::kPacked);
+    MatPtrT<float>& Q = activations_.attention.vit_Q;
+    MatPtrT<float>& K = activations_.attention.vit_K;
+    MatPtrT<float>& C = activations_.attention.vit_C;
 
     // Initialize att_out to zero prior to head loop.
     ZeroInit(activations_.attention.att_out);