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UserspaceEmulator: Add a very simple instruction fetch cache

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To avoid MMU region lookup on every single instruction fetch, we now
cache a raw pointer to the current instruction. This gets automatically
invalidated when we jump somewhere, but as long as we're executing
sequentially, instruction fetches will hit the cache and bypass all
the region lookup stuff.

This is about a ~2x speedup. :^)
This commit is contained in:
Andreas Kling 2020-07-13 20:14:14 +02:00
parent c8d3f8cdeb
commit 8656835935
5 changed files with 44 additions and 4 deletions
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27
DevTools/UserspaceEmulator/SoftCPU.cpp
View file

@ -61,23 +61,44 @@ void SoftCPU::dump() const
printf("o=%u s=%u z=%u a=%u p=%u c=%u\n", of(), sf(), zf(), af(), pf(), cf());
}
void SoftCPU::update_code_cache()
{
auto* region = m_emulator.mmu().find_region({ cs(), eip() });
ASSERT(region);
m_cached_code_ptr = region->cacheable_ptr(eip() - region->base());
m_cached_code_end = region->cacheable_ptr(region->size());
}
u8 SoftCPU::read8()
{
auto value = read_memory8({ cs(), eip() });
if (!m_cached_code_ptr || m_cached_code_ptr >= m_cached_code_end)
update_code_cache();
u8 value = *m_cached_code_ptr;
m_cached_code_ptr += 1;
m_eip += 1;
return value;
}
u16 SoftCPU::read16()
{
auto value = read_memory16({ cs(), eip() });
if (!m_cached_code_ptr || (m_cached_code_ptr + 2) >= m_cached_code_end)
update_code_cache();
u16 value = *reinterpret_cast<const u16*>(m_cached_code_ptr);
m_cached_code_ptr += 2;
m_eip += 2;
return value;
}
u32 SoftCPU::read32()
{
auto value = read_memory32({ cs(), eip() });
if (!m_cached_code_ptr || (m_cached_code_ptr + 4) >= m_cached_code_end)
update_code_cache();
u32 value = *reinterpret_cast<const u32*>(m_cached_code_ptr);
m_cached_code_ptr += 4;
m_eip += 4;
return value;
}