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common : add common_speculative_is_compat() #19270

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Merged
ggerganov merged 3 commits into from
Feb 6, 2026
Merged

common : add common_speculative_is_compat() #19270

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d30e59b
llama : add llama_memory_can_rm_suffix()
ggerganov Feb 2, 2026
1f8d0c8
Revert "llama : add llama_memory_can_rm_suffix()"
ggerganov Feb 4, 2026
46c3bb1
spec : check if the target context is compatible for spec decoding
ggerganov Feb 4, 2026
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36 changes: 36 additions & 0 deletions common/speculative.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -797,6 +797,42 @@ 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(
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4 changes: 4 additions & 0 deletions common/speculative.h
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Expand Up @@ -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);
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7 changes: 6 additions & 1 deletion tools/server/server-context.cpp
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Expand Up @@ -740,6 +740,11 @@ struct server_context_impl {

slots.clear();

const bool can_spec = common_speculative_is_compat(ctx);
if (!can_spec) {
SRV_WRN("%s", "speculative decoding not supported by this context\n");
}

// initialize slots
for (int i = 0; i < params_base.n_parallel; i++) {
server_slot slot;
Expand All @@ -752,7 +757,7 @@ struct server_context_impl {
slot.prompt.tokens.has_mtmd = mctx != nullptr;

// try speculative decoding
{
if (can_spec) {
slot.spec = common_speculative_init(params_base.speculative, slot.ctx);
if (slot.spec) {
if (mctx) {
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