How enter this optimization path?

[zljj...@gmail.com]

Hi, 

https://chromium.googlesource.com/v8/v8.git/+/refs/tags/12.0.52/src/compiler/js-typed-lowering.cc#565

How to enter this optimaization path: JSAdd(x:string, y) => JSAdd(x, JSToString(y)) or 

JSAdd(x, y:string) => JSAdd(JSToString(x), y)  ?  The code below cannot enter this optimazation path, for input type is unknow.

function add2(a, b) {
  return a + b;
}
// should create feedback vector at first, or type info can not collect.
%PrepareFunctionForOptimization(add2);
console.log(add2(1, "hello"));
%OptimizeFunctionOnNextCall(add2);
console.log(add2(2, "world"));

[Leszek Swirski]

Hi,

Most likely there would need to be some type inference inferring that one of the inputs is a string, like an operation with known string result, e.g.

function add2(a, b) {

  let x = a + "string";
  return x + b; // This would become JSAdd(x, JSToString(b)) 
}

Hope that helps,

Leszek

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[dmerc...@google.com]

Hi,

Interestingly, even

    function Foo(s) {
      return s + "42";
    }

Is enough to reach this case.

Basically, as Leszek said, this happens when we have generic JSAdd and we can infer that one of the inputs is a String.

In your example ("a + b"), we don't go into this path because we cannot infer the types of the inputs (the inputs are just Parameter[1] and Parameter[2], and we don't have feedback for parameters, just for operations). Still, because we have String feedback on the JSAdd, we decide a few lines later that we'll check that the inputs are string and we'll emit a StringConcat: https://chromium.googlesource.com/v8/v8.git/+/refs/tags/12.0.52/src/compiler/js-typed-lowering.cc#581.

Cheers,

Darius

[liang zhou]

Very detailed, thanks a lot

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