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Optimize build_jumpdest_map() #308

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Apr 27, 2021
Merged

Optimize build_jumpdest_map() #308

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12 changes: 6 additions & 6 deletions lib/evmone/baseline.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,17 +12,17 @@ namespace evmone
{
JumpdestMap build_jumpdest_map(const uint8_t* code, size_t code_size)
{
// Bitmask for PUSH opcode identification.
// It clears the lower 5 bits of a byte.
// The opcode is PUSH iff remaining byte value is 0x60 (OP_PUSH1).
constexpr auto push_op_mask = 0xE0;
// To find if op is any PUSH opcode (OP_PUSH1 <= op <= OP_PUSH32)
// it can be noticed that OP_PUSH32 is INT8_MAX (0x7f) therefore
// static_cast<int8_t>(op) <= OP_PUSH32 is always true and can be skipped.
static_assert(OP_PUSH32 == std::numeric_limits<int8_t>::max());

JumpdestMap map(code_size); // Allocate and init bitmap with zeros.
for (size_t i = 0; i < code_size; ++i)
{
const auto op = code[i];
if ((op & push_op_mask) == OP_PUSH1) // If any PUSH opcode.
i += op - size_t{OP_PUSH1 - 1}; // Skip PUSH data.
if (static_cast<int8_t>(op) >= OP_PUSH1) // If any PUSH opcode (see explanation above).
i += op - size_t{OP_PUSH1 - 1}; // Skip PUSH data.
else if (INTX_UNLIKELY(op == OP_JUMPDEST))
map[i] = true;
}
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