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LibJS: Only use bitfields in Bytecode::Operand on aarch64

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It seems both aarch64 and x86_64 are extremely sensitive to the use of
bitfields here. Unfortunately, aarch64 gains a huge speedup from them
while x86_64 sees a very noticeable slowdown.

Since we're talking about 5%+ swings in both directions here, let's go
for the best of both worlds and use ifdefs in the Operand memory layout.
This commit is contained in:
Andreas Kling 2025-04-06 12:17:20 +02:00 • committed by Andreas Kling
parent 2810071a9c
commit c7bba505ea
Notes: github-actions[bot] 2025-04-06 12:15:32 +00:00
1 changed files with 14 additions and 0 deletions
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14
Libraries/LibJS/Bytecode/Operand.h
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@ -26,7 +26,9 @@ public:
: m_type(type)
, m_index(index)
{
#if ARCH(AARCH64)
VERIFY((index & 0x3fffffff) == index);
#endif
}
explicit Operand(Register);
@ -43,11 +45,23 @@ public:
void offset_index_by(u32 offset) { m_index += offset; }
private:
// NOTE: aarch64 gets much faster with bitfields here, while x86_64 gets slower.
// Because this type is absolutely essential to the interpreter, we allow
// ourselves this little ifdef.
#if ARCH(AARCH64)
Type m_type : 2 {};
u32 m_index : 30 { 0 };
#else
Type m_type { Type::Invalid };
u32 m_index { 0 };
#endif
};
#if ARCH(AARCH64)
static_assert(sizeof(Operand) == 4);
#else
static_assert(sizeof(Operand) == 8);
#endif
}