Merge branch 'upstream' into concedo_experimental

# Conflicts:
#	.github/workflows/build.yml
#	docs/ops.md
#	docs/ops/SYCL.csv
#	ggml/src/ggml-sycl/element_wise.cpp
#	ggml/src/ggml-sycl/ggml-sycl.cpp
#	ggml/src/ggml-webgpu/ggml-webgpu-shader-lib.hpp
#	ggml/src/ggml-webgpu/ggml-webgpu.cpp
#	pyproject.toml
#	requirements/requirements-convert_legacy_llama.txt
#	src/CMakeLists.txt
#	src/llama-vocab.cpp
#	tests/test-backend-ops.cpp

Author: LostRuins

common/speculative.cpp

@@ -805,6 +805,42 @@ enum common_speculative_type common_speculative_type_from_name(const std::string
     return it->second;
 }
 
+bool common_speculative_is_compat(llama_context * ctx_tgt) {
+    auto * mem = llama_get_memory(ctx_tgt);
+    if (mem == nullptr) {
+        return false;
+    }
+
+    bool res = true;
+
+    llama_memory_clear(mem, true);
+
+    // eval 2 tokens to check if the context is compatible
+    std::vector<llama_token> tmp;
+    tmp.push_back(0);
+    tmp.push_back(0);
+
+    int ret = llama_decode(ctx_tgt, llama_batch_get_one(tmp.data(), tmp.size()));
+    if (ret != 0) {
+        LOG_ERR("%s: llama_decode() failed: %d\n", __func__, ret);
+        res = false;
+        goto done;
+    }
+
+    // try to remove the last tokens
+    if (!llama_memory_seq_rm(mem, 0, 1, -1)) {
+        LOG_WRN("%s: the target context does not support partial sequence removal\n", __func__);
+        res = false;
+        goto done;
+    }
+
+done:
+    llama_memory_clear(mem, true);
+    llama_synchronize(ctx_tgt);
+
+    return res;
+}
+
 // initialization of the speculative decoding system
 //
 common_speculative * common_speculative_init(

common/speculative.h

@@ -14,6 +14,10 @@ enum common_speculative_type common_speculative_type_from_name(const std::string
 // convert type to string
 std::string common_speculative_type_to_str(enum common_speculative_type type);
 
+// check if the llama_context is compatible for speculative decoding
+// note: clears the memory of the context
+bool common_speculative_is_compat(llama_context * ctx_tgt);
+
 common_speculative * common_speculative_init(
         common_params_speculative & params,
         llama_context             * ctx_tgt);

convert_hf_to_gguf.py

@@ -394,7 +394,7 @@ bool ggml_metal_cpy_tensor_async(ggml_metal_t ctx_src, ggml_metal_t ctx_dst, con
         [encoder endEncoding];
 
         ggml_metal_event_t ev_cpy = ggml_metal_get_ev_cpy(ctx_src);
-        ggml_metal_event_record(ctx_src, ev_cpy);
+        ggml_metal_event_encode_signal(ev_cpy, cmd_buf);
 
         [cmd_buf commit];
 

ggml/src/ggml-metal/ggml-metal-context.m

@@ -5285,6 +5285,7 @@ constant int32_t FC_flash_attn_ext_blk_ncpsg [[function_constant(FC_FLASH_ATTN_E
 // scan the blocks of the mask that are not masked
 // 0 -     masked (i.e. full of -INF, skip)
 // 1 - not masked (i.e. at least one element of the mask is not -INF)
+// 2 - all zero
 kernel void kernel_flash_attn_ext_blk(
         constant ggml_metal_kargs_flash_attn_ext_blk & args,
         device const char * mask,
@@ -5306,27 +5307,29 @@ kernel void kernel_flash_attn_ext_blk(
 
     device const half * mask_src = (device const half *) (mask + (i1*Q)*args.nb31 + i2*args.nb32 + i3*args.nb33) + i0*C + tiisg;
 
-    // fast route
-    if (res == 0) {
-        if (simd_max(*mask_src) > -MAXHALF/2) {
-            res = 1;
-        }
-    }
-
     // detailed check of the elements of the block
     if ((C > NW || Q > 1) && res == 0) {
-        half m = -MAXHALF;
+        half mmin =  MAXHALF;
+        half mmax = -MAXHALF;
 
         FOR_UNROLL (short j = 0; j < Q; ++j) {
             FOR_UNROLL (short ii = 0; ii < C/NW; ++ii) {
-                m = max(m, mask_src[ii*NW]);
+                mmin = min(mmin, mask_src[ii*NW]);
+                mmax = max(mmax, mask_src[ii*NW]);
             }
 
             mask_src += args.nb31/2;
         }
 
-        if (simd_max(m) > -MAXHALF/2) {
-            res = 1;
+        mmin = simd_min(mmin);
+        mmax = simd_max(mmax);
+
+        if (mmax > -MAXHALF) {
+            if (mmin == 0.0 && mmax == 0.0) {
+                res = 2;
+            } else {
+                res = 1;
+            }
         }
     }
 
@@ -5568,26 +5571,36 @@ void kernel_flash_attn_ext_impl(
                 ic = 0;
             }
 
+            char blk_cur = 1;
+
             // read the mask into shared mem
             if (FC_flash_attn_ext_has_mask) {
-                if (blk[ic0] == 0) {
+                blk_cur = blk[ic0];
+
+                if (blk_cur == 0) {
                     FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
                         pm2[jj] += NW;
                     }
 
                     continue;
                 }
 
-                FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
-                    const short j = jj*NSG + sgitg;
+                if (blk_cur == 1) {
+                    FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
+                        const short j = jj*NSG + sgitg;
 
-                    if (FC_flash_attn_ext_bc_mask) {
-                        sm2[j*SH + tiisg] = (iq1 + j) < args.ne31 ? pm2[jj][tiisg] : half2(-MAXHALF, -MAXHALF);
-                    } else {
-                        sm2[j*SH + tiisg] = pm2[jj][tiisg];
-                    }
+                        if (FC_flash_attn_ext_bc_mask) {
+                            sm2[j*SH + tiisg] = (iq1 + j) < args.ne31 ? pm2[jj][tiisg] : half2(-MAXHALF, -MAXHALF);
+                        } else {
+                            sm2[j*SH + tiisg] = pm2[jj][tiisg];
+                        }
 
-                    pm2[jj] += NW;
+                        pm2[jj] += NW;
+                    }
+                } else if (blk_cur == 2) {
+                    FOR_UNROLL (short jj = 0; jj < NQ; ++jj) {
+                        pm2[jj] += NW;
+                    }
                 }
 
 #if 0
@@ -5752,10 +5765,12 @@ void kernel_flash_attn_ext_impl(
                 }
 
                 // mqk = mqk + slope*mask
-                if (FC_flash_attn_ext_has_bias) {
-                    s2 += s2_t(sm2[j*SH + tiisg])*slope;
-                } else {
-                    s2 += s2_t(sm2[j*SH + tiisg]);
+                if (blk_cur != 2) {
+                    if (FC_flash_attn_ext_has_bias) {
+                        s2 += s2_t(sm2[j*SH + tiisg])*slope;
+                    } else {
+                        s2 += s2_t(sm2[j*SH + tiisg]);
+                    }
                 }
 
                 M[jj] = simd_max(max(M[jj], max(s2[0], s2[1])));

ggml/src/ggml-metal/ggml-metal.metal

@@ -418,19 +418,19 @@ enum FaCodePath {
 };
 
 struct vk_fa_pipeline_state {
-    vk_fa_pipeline_state(uint32_t HSK, uint32_t HSV, bool small_rows, bool small_cache, FaCodePath path, bool aligned, bool f32acc, bool use_mask_opt)
-        : HSK(HSK), HSV(HSV), small_rows(small_rows), small_cache(small_cache), path(path), aligned(aligned), f32acc(f32acc), use_mask_opt(use_mask_opt) {}
+    vk_fa_pipeline_state(uint32_t HSK, uint32_t HSV, bool small_rows, bool small_cache, FaCodePath path, bool aligned, bool f32acc, uint32_t flags)
+        : HSK(HSK), HSV(HSV), small_rows(small_rows), small_cache(small_cache), path(path), aligned(aligned), f32acc(f32acc), flags(flags) {}
 
     uint32_t HSK, HSV;
     bool small_rows, small_cache;
     FaCodePath path;
     bool aligned;
     bool f32acc;
-    bool use_mask_opt;
+    uint32_t flags;
 
     bool operator<(const vk_fa_pipeline_state &b) const {
-        return std::tie(HSK, HSV, small_rows, small_cache, path, aligned, f32acc, use_mask_opt) <
-               std::tie(b.HSK, b.HSV, b.small_rows, b.small_cache, b.path, b.aligned, b.f32acc, b.use_mask_opt);
+        return std::tie(HSK, HSV, small_rows, small_cache, path, aligned, f32acc, flags) <
+               std::tie(b.HSK, b.HSV, b.small_rows, b.small_cache, b.path, b.aligned, b.f32acc, b.flags);
     }
 };
 
@@ -3209,7 +3209,7 @@ static void ggml_vk_load_shaders(vk_device& device) {
         return {fa_rows_cols(path, hsk, hsv, clamp, type, small_rows, small_cache)[0], 1, 1};
     };
 
-    auto const &fa_spec_constants = [&](FaCodePath path, uint32_t hsk, uint32_t hsv, uint32_t clamp, ggml_type type, bool small_rows, bool small_cache, bool use_mask_opt) -> std::vector<uint32_t> {
+    auto const &fa_spec_constants = [&](FaCodePath path, uint32_t hsk, uint32_t hsv, uint32_t clamp, ggml_type type, bool small_rows, bool small_cache, uint32_t flags) -> std::vector<uint32_t> {
         // For large number of rows, 128 invocations seems to work best.
         // For small number of rows (e.g. N==1), 256 works better. But matrix granularity for 256 is 32, so we
         // can't use 256 for D==80.
@@ -3241,7 +3241,7 @@ static void ggml_vk_load_shaders(vk_device& device) {
         // AMD prefers loading K directly from global memory
         const uint32_t k_load_shmem = device->vendor_id == VK_VENDOR_ID_NVIDIA && hsk < 256 ? 1 : 0;
 
-        return {wg_size, rows_cols[0], rows_cols[1], hsk, hsv, clamp, D_split, device->subgroup_size, k_load_shmem, use_mask_opt};
+        return {wg_size, rows_cols[0], rows_cols[1], hsk, hsv, clamp, D_split, device->subgroup_size, k_load_shmem, flags};
     };
 
 #define CREATE_FA(TYPE, NAMELC, FAPATH, SUFFIX) \
@@ -3253,19 +3253,19 @@ static void ggml_vk_load_shaders(vk_device& device) {
             FaCodePath path = fa.first.path; \
             bool aligned = fa.first.aligned; \
             bool f32acc = fa.first.f32acc; \
-            bool use_mask_opt = fa.first.use_mask_opt; \
+            uint32_t flags = fa.first.flags; \
             if (path == FAPATH) { \
                 if (aligned) { \
                     if (f32acc) { \
-                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f32acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache,use_mask_opt), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
+                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f32acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache,flags), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
                     } else { \
-                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f16acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache,use_mask_opt), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
+                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f16acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache,flags), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
                     } \
                 } else { \
                     if (f32acc) { \
-                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f32acc"         #NAMELC, flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache,use_mask_opt), 1,                                        true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
+                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f32acc"         #NAMELC, flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ##            SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache,flags), 1,                                        true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
                     } else { \
-                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f16acc"         #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache,use_mask_opt), 1,                                        true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
+                        ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f16acc"         #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len,  flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data,  "main", 7, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache,flags), 1,                                        true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0));     \
                     } \
                 } \
             } \
@@ -8633,10 +8633,26 @@ static void ggml_vk_flash_attn(ggml_backend_vk_context * ctx, vk_context& subctx
 
     bool f32acc = path == FA_SCALAR || dst->op_params[3] == GGML_PREC_F32;
 
+    float scale         = 1.0f;
+    float max_bias      = 0.0f;
+    float logit_softcap = 0.0f;
+
+    memcpy(&scale,         (const float *) dst->op_params + 0, sizeof(float));
+    memcpy(&max_bias,      (const float *) dst->op_params + 1, sizeof(float));
+    memcpy(&logit_softcap, (const float *) dst->op_params + 2, sizeof(float));
+
+    if (logit_softcap != 0) {
+        scale /= logit_softcap;
+    }
+
     // Only use mask opt when the mask is fairly large. This hasn't been tuned extensively.
     bool use_mask_opt = mask && nem1 >= 32 && nem0 * nem1 > 32768;
 
-    vk_fa_pipeline_state fa_pipeline_state(HSK, HSV, small_rows, small_cache, path, aligned, f32acc, use_mask_opt);
+    uint32_t flags = (use_mask_opt       ? 1 : 0) |
+                     (mask != nullptr    ? 2 : 0) |
+                     (logit_softcap != 0 ? 4 : 0);
+
+    vk_fa_pipeline_state fa_pipeline_state(HSK, HSV, small_rows, small_cache, path, aligned, f32acc, flags);
 
     vk_pipeline pipeline = nullptr;
 
@@ -8716,18 +8732,6 @@ static void ggml_vk_flash_attn(ggml_backend_vk_context * ctx, vk_context& subctx
         }
     }
 
-    float scale         = 1.0f;
-    float max_bias      = 0.0f;
-    float logit_softcap = 0.0f;
-
-    memcpy(&scale,         (const float *) dst->op_params + 0, sizeof(float));
-    memcpy(&max_bias,      (const float *) dst->op_params + 1, sizeof(float));
-    memcpy(&logit_softcap, (const float *) dst->op_params + 2, sizeof(float));
-
-    if (logit_softcap != 0) {
-        scale /= logit_softcap;
-    }
-
     const uint32_t n_head_kv   = neq2;
     const uint32_t n_head_log2 = 1u << (uint32_t) floorf(log2f((float) n_head_kv));
     const float m0 = powf(2.0f, -(max_bias       ) / n_head_log2);
@@ -8741,7 +8745,7 @@ static void ggml_vk_flash_attn(ggml_backend_vk_context * ctx, vk_context& subctx
     vk_subbuffer sinks_buf = sinks ? ggml_vk_tensor_subbuffer(ctx, sinks) : q_buf;
     vk_subbuffer mask_opt_buf = use_mask_opt ? ggml_vk_subbuffer(ctx, ctx->prealloc_y, 0) : q_buf;
 
-    uint32_t mask_n_head_log2 = ((sinks != nullptr) << 24) | ((mask != nullptr) << 16) | n_head_log2;
+    uint32_t mask_n_head_log2 = ((sinks != nullptr) << 24) | n_head_log2;
 
     if (use_mask_opt)
     {

ggml/src/ggml-vulkan/ggml-vulkan.cpp

@@ -127,7 +127,7 @@ void main() {
             continue;
         }
         // Only load if the block is not all zeros
-        if ((p.mask_n_head_log2 & MASK_ENABLE_BIT) != 0 && mask_opt_bits != MASK_OPT_ALL_ZERO) {
+        if (MASK_ENABLE && mask_opt_bits != MASK_OPT_ALL_ZERO) {
             bool nem1_bounds_check = !(p.gqa_ratio > 1) && (p.nem1 % Br) != 0;
 
             [[unroll]] for (uint32_t idx = 0; idx < Bc * Br; idx += gl_WorkGroupSize.x) {
@@ -181,15 +181,15 @@ void main() {
             }
         }
 
-        if (p.logit_softcap != 0.0f) {
+        if (LOGIT_SOFTCAP) {
             [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                 [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                     Sf[r][c] = p.logit_softcap * tanh(Sf[r][c]);
                 }
             }
         }
 
-        if ((p.mask_n_head_log2 & MASK_ENABLE_BIT) != 0 && mask_opt_bits != MASK_OPT_ALL_ZERO) {
+        if (MASK_ENABLE && mask_opt_bits != MASK_OPT_ALL_ZERO) {
             [[unroll]] for (uint32_t c = 0; c < cols_per_thread; ++c) {
                 [[unroll]] for (uint32_t r = 0; r < Br; ++r) {
                     float mvf = masksh[c * cols_per_iter + col_tid][r];

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

@@ -10,7 +10,11 @@ layout (constant_id = 5) const uint32_t Clamp = 0;
 layout (constant_id = 6) const uint32_t D_split = 16;
 layout (constant_id = 7) const uint32_t SubGroupSize = 32;
 layout (constant_id = 8) const uint32_t K_LOAD_SHMEM = 0;
-layout (constant_id = 9) const bool     USE_MASK_OPT = false;
+layout (constant_id = 9) const uint32_t Flags = 0;
+
+const bool USE_MASK_OPT  = (Flags & 1) != 0;
+const bool MASK_ENABLE   = (Flags & 2) != 0;
+const bool LOGIT_SOFTCAP = (Flags & 4) != 0;
 
 // Round up head sizes to a multiple of 16, for coopmat1/coopmat2 paths
 const uint32_t HSK_pad = (HSK + 15) & ~15;
@@ -60,7 +64,6 @@ layout (push_constant) uniform parameter {
 } p;
 
 #define SINK_ENABLE_BIT (1<<24)
-#define MASK_ENABLE_BIT (1<<16)
 #define N_LOG2_MASK 0xFFFF
 
 layout (binding = 4) readonly buffer S {float data_s[];};
@@ -237,3 +240,7 @@ void init_indices()
     // and breaking the alignment detection.
     m_stride = (p.gqa_ratio > 1) ? (p.gqa_ratio >> 16) : KV;
 }
+
+// Bias applied to softmax to stay in fp16 range.
+// Based on ggml-cuda issue https://github.com/ggml-org/llama.cpp/issues/18606
+const float FATTN_KQ_MAX_OFFSET = 3.0f*0.6931f;

ggml/src/ggml-vulkan/vulkan-shaders/flash_attn_base.glsl

@@ -160,7 +160,7 @@ void main() {
             mask_cache[idx] = f16vec4(0);
         }
 
-        if ((p.mask_n_head_log2 & MASK_ENABLE_BIT) != 0) {
+        if (MASK_ENABLE) {
 
             if (USE_MASK_OPT && mask_opt_idx != j / 16) {
                 mask_opt_idx = j / 16;
@@ -303,7 +303,7 @@ void main() {
         coopMatStore(SfMat, sfsh, coord, sfshstride, gl_CooperativeMatrixLayoutRowMajor);
         barrier();
 
-        if (p.logit_softcap != 0.0f) {
+        if (LOGIT_SOFTCAP) {
             [[unroll]] for (uint32_t idx = 0; idx < Bc * Br / 4; idx += gl_WorkGroupSize.x) {
                 uint32_t c = (idx + tid) / (Br / 4);
                 uint32_t r = (idx + tid) % (Br / 4);
@@ -314,7 +314,7 @@ void main() {
             barrier();
         }
 
-        if ((p.mask_n_head_log2 & MASK_ENABLE_BIT) != 0) {
+        if (MASK_ENABLE) {
             [[unroll]] for (uint32_t idx = 0; idx < Bc * Br / 4; idx += gl_WorkGroupSize.x) {
                 uint32_t c = (idx + tid) / (Br / 4);
                 uint32_t r = (idx + tid) % (Br / 4);