Compiler optimisation removes variable assignment

[samisalreadytaken]

Local variable assignment to adjacent local variables in comma separated declarations ignore the first variable's assignment and cause it to have no value.

// a = null
// b = 1
local a = 1, b = a;

-----LOCALS
[2] b   1 0
[1] a   1 0
[0] this    0 1
-----dump
[000]     _OP_LOADINT 2 1 0 0

The source of this issue is at SQFuncState::AddInstruction() https://github.com/albertodemichelis/squirrel/blob/7da4a6f196cc4e45f753a46cf0b0a9c125df34e2/squirrel/sqfuncstate.cpp#L519-L530

reached from SQCompiler::LocalDeclStatement() https://github.com/albertodemichelis/squirrel/blob/7da4a6f196cc4e45f753a46cf0b0a9c125df34e2/squirrel/sqcompiler.cpp#L1067

Removing if(pi._arg0 == i._arg1) block compiles it identical to local a = 1; local b = a; with optimisations.

-----LOCALS
[2] b   2 1
[1] a   1 1
[0] this    0 2
-----dump
[000]     _OP_LOADINT 1 1 0 0
[001]        _OP_MOVE 2 1 0 0

This can be observed with _OP_GET and other instructions listed there. _OP_GET actually assigns the GET-index to the variable.

this[1337] <- "x";

// a = 1337
// b = "x"
local a = this[1337], b = a;

-----LOCALS
[2] b   2 1
[1] a   2 1
[0] this    0 2
-----dump
[000]     _OP_LOADINT 1 1337 0 0
[001]         _OP_GET 2 0 1 0

With more variables

// a = 1
// b = null
// c = 1
local a = 1, b = 1, c = b;

-----LOCALS
[3] c   2 1
[2] b   2 1
[1] a   1 1
[0] this    0 2
-----dump
[000]     _OP_LOADINT 1 1 0 0
[001]     _OP_LOADINT 3 1 0 0

Two move instructions in a row are compiled into _OP_DMOVE, which works fine. Note how c is assigned to a, as assigning it to b causes the issue.

// a = 1
// b = 1
// c = 1
// d = 1
local a = 1, b = 1, c = a, d = c;

-----LOCALS
[4] d   3 2
[3] c   3 2
[2] b   2 2
[1] a   1 2
[0] this    0 3
-----dump
[000]     _OP_LOADINT 1 1 0 0
[001]     _OP_LOADINT 2 1 0 0
[002]       _OP_DMOVE 3 1 4 3

[albertodemichelis]

I'll look into this, thank you.

[albertodemichelis]

I fixed it