About LdaSmiExtraWideHandler

[yahan lu]

Hi all~

I'm studying the builtin::LdaSmiExtraWideHandler and want to understand its implementation. However, I can only find source code for the standard LdaSmi handler:

// LdaSmi <imm> // // Load an integer literal into the accumulator as a Smi. IGNITION_HANDLER(LdaSmi, InterpreterAssembler) { TNode<Smi> smi_int = BytecodeOperandImmSmi(0); SetAccumulator(smi_int); Dispatch(); }

Where should I look for the LdaSmiExtraWideHandler implementation?

[Marja Hölttä]

Some pointers:

By searching for "ExtraWide" in code search you can see e.g., this test code snippet:

https://source.chromium.org/chromium/chromium/src/+/main:v8/test/unittests/interpreter/bytecode-decoder-unittest.cc;l=32?q=extrawide&ss=chromium%2Fchromium%2Fsrc

which tells us how the ExtraWide is used.

The handler for ExtraWide is:

https://source.chromium.org/chromium/chromium/src/+/main:v8/src/interpreter/interpreter-generator.cc;l=3308

I hope this helps.

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[Leszek Swirski]

Exactly, as Marja said, "ExtraWide" is a separate bytecode that puts the interpreter into "ExtraWide" mode for the next dispatch (by changing the dispatch table). Then, each IGNITION_HANDLER defined bytecode has a Wide and ExtraWide equivalent, which are all generated from the same source; the LdaSmi you linked below is generated three times, with BytecodeOperandImmSmi behaving differently for each generation (as controlled by "operand_scale()" in https://source.chromium.org/chromium/chromium/src/+/main:v8/src/interpreter/interpreter-assembler.cc;l=593;drc=0dc30698370bcde67dda4f48b7ca19bf4c1dbc17)

To view this discussion visit https://groups.google.com/d/msgid/v8-dev/CAED6dUAzD2Hq5adX1SsAMCC89R93ktKYqWLWQ2-MCwNB0iQw8Q%40mail.gmail.com.