Incorrect execution when using a direct access variable as a function argument

[chen4s666]

Hello, I found an error while using direct access variables. If a direct-access variable is used as an argument to output or intout, the direct-access variable cannot be returned modified.
You can see in the screenshot below that on the left is the ST code I wrote and on the right is the generated ir code. In the processing of the ir code, %5 is used to store the value of xx.%X1 and pass its pointer to the function, but the value of %5 is not stored back to xx.%X1. I don't know if this is intentional, or if it's a bug.

I've pasted the code here for easy presentation

PROGRAM main
VAR
xx:INT;
END_VAR
fc1(aa=>xx.%X1);
END_PROGRAM
FUNCTION fc1:BOOL
VAR_OUTPUT
aa:BOOL;
END_VAR
END_FUNCTION

%main = type { i16 }
@main_instance = global %main zeroinitializer
define void @main(%main* %0) section "fn-main:v" {
entry:
%xx = getelementptr inbounds %main, %main* %0, i32 0, i32 0
%load_xx = load i16, i16* %xx, align 2
%shift = ashr i16 %load_xx, 1
%1 = trunc i16 %shift to i8
%2 = and i8 %1, 1
%load_xx1 = load i16, i16* %xx, align 2
%shift2 = ashr i16 %load_xx1, 1
%3 = trunc i16 %shift2 to i8
%4 = and i8 %3, 1
%5 = alloca i8, align 1
store i8 %4, i8* %5, align 1
%call = call i8 @fc1(i8* %5)
ret void
}
define i8 @fc1(i8* %0) section "fn-fc1:u8[pu8]" {
entry:
%fc1 = alloca i8, align 1
%aa = alloca i8*, align 8
store i8* %0, i8** %aa, align 8
store i8 0, i8* %fc1, align 1
%fc1_ret = load i8, i8* %fc1, align 1
ret i8 %fc1_ret
}

[ghaith]

Hi, chen thank you for the report. I remember we were working on a similar issue recently. @volsa is this the same issue you were working on?

[volsa]

Hi @chen4s666 , VAR_OUTPUT is only supported for FUNCTION_BLOCKs. Changing your code to

PROGRAM main
    VAR
        xx : INT;
        fc1_instance : fc1;
    END_VAR

    fc1_instance(aa => xx.%X1);
END_PROGRAM

FUNCTION_BLOCK fc1
    VAR_OUTPUT
        aa : BOOL := TRUE;
    END_VAR
END_FUNCTION_BLOCK

should fix your issue. That being said, there is currently an issue on master which is being fixed with this PR. The PR should be merged soon-ish however.

[chen4s666]

Thank you.Maybe I misunderstood what you meant.I don't understand why you want me to change FUNCTION to FUNCTION_BLOCK, because FUNCTION doesn't support VAR_OUTPUT attribute?

[volsa]

Sorry, I had another issue on my mind which I confused with this one. VAR_OUTPUT in fact works for functions, but as you've correctly identified there's some logic missing to store back the results when using direct access in output assignments. This is definetly a bug and I've opened an issue for it. However, we happen to generate the correct code for FUNCTION_BLOCKs (at least in this branch), which you can use in the meantime until this issue fixed.