On Fri, Apr 30, 2021 at 10:51 AM 'Valentin Deleplace' via golang-nuts
<golang-nuts@googlegroups.com> wrote:
>
> Hi, I was surprised that the funcs f and g do not generate the same assembly
> code:
>
> func f() string {
> s := "a" + "b"
> return s
> }
>
> func g() string {
> s := "a"
> s += "b"
> return s
> }
>
> The compiled assembly respects the apparent instructions of the source code,
> with g calling runtime.concatstring2, while f does not (f benefits from an
> optimization that transforms "a"+"b" into the constant "ab").
>
> I don't know exactly what SSA does in the compiler, but I thought it would be
> capable of optimizing f and g into the exact same generated code. Am I
> missing something?
I agree that the compiler ought to be able to generate the same code
for both cases. But I'll note that from a language perspective, the
functions are quite different. "a" + "b" is a constant expression
(https://golang.org/ref/spec#Constant_expressions). The language
requires that "a" + "b" be evaluated at compile time. There is no
such requirement for the function g. That would require a more
complicated compiler optimization.
Ian
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