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LibJS/Bytecode: Increase coverage of left/shift expression fast paths

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As long as the inputs are Int32, we can convert them to UInt32 in a
spec-compliant way with a simple static_cast<u32>.

This allows calculations like `-3 >>> 2` to take the fast path as well,
which is extremely valuable for stuff like crypto code.

While we're doing this, also remove the fast paths from the generic
shift functions in Value.cpp, since we only end up there if we *didn't*
take the same fast path in the interpreter.
This commit is contained in:
Andreas Kling 2024-03-04 10:56:21 +01:00
parent a5e1e66abc
commit 17c1f742a9
2 changed files with 3 additions and 15 deletions
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6
Userland/Libraries/LibJS/Bytecode/Interpreter.cpp
View file

@ -841,7 +841,7 @@ ThrowCompletionOr<void> UnsignedRightShift::execute_impl(Bytecode::Interpreter&
auto& vm = interpreter.vm();
auto const lhs = interpreter.get(m_lhs);
auto const rhs = interpreter.get(m_rhs);
if (lhs.is_int32() && rhs.is_int32() && lhs.as_i32() >= 0 && rhs.as_i32() >= 0) {
if (lhs.is_int32() && rhs.is_int32()) {
auto const shift_count = static_cast<u32>(rhs.as_i32()) % 32;
interpreter.set(m_dst, Value(static_cast<u32>(lhs.as_i32()) >> shift_count));
return {};
@ -855,7 +855,7 @@ ThrowCompletionOr<void> RightShift::execute_impl(Bytecode::Interpreter& interpre
auto& vm = interpreter.vm();
auto const lhs = interpreter.get(m_lhs);
auto const rhs = interpreter.get(m_rhs);
if (lhs.is_int32() && rhs.is_int32() && rhs.as_i32() >= 0) {
if (lhs.is_int32() && rhs.is_int32()) {
auto const shift_count = static_cast<u32>(rhs.as_i32()) % 32;
interpreter.set(m_dst, Value(lhs.as_i32() >> shift_count));
return {};
@ -869,7 +869,7 @@ ThrowCompletionOr<void> LeftShift::execute_impl(Bytecode::Interpreter& interpret
auto& vm = interpreter.vm();
auto const lhs = interpreter.get(m_lhs);
auto const rhs = interpreter.get(m_rhs);
if (lhs.is_int32() && rhs.is_int32() && rhs.as_i32() >= 0) {
if (lhs.is_int32() && rhs.is_int32()) {
auto const shift_count = static_cast<u32>(rhs.as_i32()) % 32;
interpreter.set(m_dst, Value(lhs.as_i32() << shift_count));
return {};

12
Userland/Libraries/LibJS/Runtime/Value.cpp
View file

@ -1598,12 +1598,6 @@ ThrowCompletionOr<Value> left_shift(VM& vm, Value lhs, Value rhs)
// ShiftExpression : ShiftExpression >> AdditiveExpression
ThrowCompletionOr<Value> right_shift(VM& vm, Value lhs, Value rhs)
{
// OPTIMIZATION: Fast path when both values are suitable Int32 values.
if (lhs.is_int32() && rhs.is_int32() && rhs.as_i32() >= 0) {
auto shift_count = static_cast<u32>(rhs.as_i32()) % 32;
return Value(lhs.as_i32() >> shift_count);
}
// 13.15.3 ApplyStringOrNumericBinaryOperator ( lval, opText, rval ), https://tc39.es/ecma262/#sec-applystringornumericbinaryoperator
// 1-2, 6. N/A.
@ -1655,12 +1649,6 @@ ThrowCompletionOr<Value> right_shift(VM& vm, Value lhs, Value rhs)
// ShiftExpression : ShiftExpression >>> AdditiveExpression
ThrowCompletionOr<Value> unsigned_right_shift(VM& vm, Value lhs, Value rhs)
{
// OPTIMIZATION: Fast path when both values are suitable Int32 values.
if (lhs.is_int32() && rhs.is_int32() && lhs.as_i32() >= 0 && rhs.as_i32() >= 0) {
auto shift_count = static_cast<u32>(rhs.as_i32()) % 32;
return Value(static_cast<u32>(lhs.as_i32()) >> shift_count);
}
// 13.15.3 ApplyStringOrNumericBinaryOperator ( lval, opText, rval ), https://tc39.es/ecma262/#sec-applystringornumericbinaryoperator
// 1-2, 5-6. N/A.