Re: [Qemu-devel] definition of struct TCGv_i64_d

[G 3]

On Oct 21, 2016, at 11:17 AM, Peter Maydell wrote:

> On 21 October 2016 at 15:48, Programmingkid  
> <address@hidden> wrote:
> > In the tcg.h file, there is this line: typedef struct TCGv_i64_d  
> > *TCGv_i64;
> >
> > Would anyone know where the definition of struct TCGv_i64_d is?
>
> There is none, because the "pointers" in these variables are
> never dereferenced. These are just magic to let us make use
> of the compiler's typechecking -- the actual values in the
> TCGv_i64 variables are integers (offsets into arrays describing
> the temporaries inside the TCG code). The only way to create a
> TCGv_i64 is with MAKE_TCGV_I64, and then you can get back to
> the underlying integer (if you're code in tcg/) is with
> GET_TCGV_I64.
>
> We used to typedef TCGv_i64 &c as plain "int"s, but then the
> compiler doesn't complain if you pass a TCGv_i32 to a function
> expecting a TCGv_i64.
>
> thanks
> -- PMM

Would you accept a patch that added a comment explaining that struct  
TCGv_i64 isn't really a structure?

I'm thinking something like this would help:

/*
	There is no TCGv_i64_d structure. This is really a way around a gcc  
issue.
        TCGv_i64 can be considered a pointer to an integer. Only  
MAKE_TCGV_I64
        can create an instance variable. GET_TCGV_I64 is what is  
used to access the value.
*/
typedef struct TCGv_i64_d *TCGv_i64;