[vm] Use `BoolToIntInstr` in `FlowGraphBuilder::BoolToInt`

[dcharkes]

Edit 2024-01-31: We should replace Fragment FlowGraphBuilder::BoolToInt to use BoolToIntInstr and implement BoolToIntInstr on the other platforms.

===== Old description =====

We could consider making IfThenElseInstr support unboxed output values.

It would remove two shifts (and a move) from the below code generated in FFI trampolines (after CL).

        ;; v111 <- IfThenElse(===, v12 T{*}, v41 ? 1 : 0) T{_Smi}
0x7f92e71a89e2    4833d2                 xorq rdx,rdx
0x7f92e71a89e5    493b9ed0000000         cmpq rbx,[thr+0xd0]   true
0x7f92e71a89ec    0f94c2                 setzl rdx
0x7f92e71a89ef    48d1e2                 shlq rdx,1
        ;; ParallelMove rbx <- rdx
0x7f92e71a89f2    4889d3                 movq rbx,rdx
        ;; v77 <- UnboxUint32([tr], [non-speculative], v111) T{int}
0x7f92e71a89f5    48d1fb                 sarq rbx,1

[alexmarkov]

We also have BoolToInt IL instruction (with code generation implemented only on RISC-V). Maybe we can extend and reuse it in FFI.

[dcharkes]

Ah, new and shiny! 👍

[vaishnavi-2901]

hey
I can work on it, please assign it to me

[dcharkes]

The other issue that you replied to is probably somewhat easier to start with, so lets do that one first. 👌

[eliphazbouye]

@dcharkes can you assign this issue to me, I want to work on it