[Mesa-dev] [PATCH] nir: Make C++ more happy with NIR_SRC_INIT and NIR_DEST_INIT

[Francisco Jerez]

Jason Ekstrand <jason at jlekstrand.net> writes:

> In C, if you partially initialize a structure, the rest of the struct gets
> set to 0.  C++, however, does not have this rule so GCC throws warnings
> whenver NIR_SRC_INIT or NIR_DEST_INIT is used in C++.

I don't think that's right, in C++ initializers missing from an
aggregate initializer list are also defined to be initialized
(value-initialized to be more precise, what would set them to zero in
this case just like in C).

> Since nir.h contains a static inline that uses NIR_SRC_INIT, every C++
> file that includes nir.h complains about this.
>
I suspect the reason why this causes a warning may be that you're using
compound literals? (which are a C99-specific feature and not part of C++)

> This patch adds a small static inline function that makes a struct,
> memsets it to 0, and returns it.  NIR_SRC_INIT and NIR_DEST_INIT are then
> wrappers around this function.

In C++ you could just call the implicitly defined default constructor
for nir_src or nir_dest, like 'nir_src()'.

> ---
>  src/glsl/nir/nir.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
>
> diff --git a/src/glsl/nir/nir.h b/src/glsl/nir/nir.h
> index c666d93..3634f30 100644
> --- a/src/glsl/nir/nir.h
> +++ b/src/glsl/nir/nir.h
> @@ -511,7 +511,18 @@ typedef struct nir_src {
>     bool is_ssa;
>  } nir_src;
>  
> +#ifdef __cplusplus
> +static inline nir_src
> +__nir_src_init(void)
> +{
> +   nir_src src;
> +   memset(&src, 0, sizeof(src));
> +   return src;
> +}
> +#define NIR_SRC_INIT (__nir_src_init())
> +#else
>  #define NIR_SRC_INIT (nir_src) { { NULL } }
> +#endif
>  
>  #define nir_foreach_use(reg_or_ssa_def, src) \
>     list_for_each_entry(nir_src, src, &(reg_or_ssa_def)->uses, use_link)
> @@ -534,7 +545,18 @@ typedef struct {
>     bool is_ssa;
>  } nir_dest;
>  
> +#ifdef __cplusplus
> +static inline nir_dest
> +__nir_dest_init(void)
> +{
> +   nir_dest dest;
> +   memset(&dest, 0, sizeof(dest));
> +   return dest;
> +}
> +#define NIR_DEST_INIT (__nir_dest_init())
> +#else
>  #define NIR_DEST_INIT (nir_dest) { { { NULL } } }
> +#endif
>  
>  #define nir_foreach_def(reg, dest) \
>     list_for_each_entry(nir_dest, dest, &(reg)->defs, reg.def_link)
> -- 
> 2.4.3
>
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