Re: [PATCH] mips: Fix up creation of MD builtins with 0 arguments [PR126484]

On Thu, 30 Jul 2026, Jakub Jelinek wrote:

> Hi!
> 
> For MIPS_SI_FTYPE_VOID and MIPS_USI_FTYPE_VOID which are meant
> for functions which return (SImode) int or unsigned int and have
> (void) arguments the MIPS backend creates those using
> case MIPS_SI_FTYPE_VOID: types[(int) type] = build_function_type_list (intSI_type_node, void_type_node, NULL_TREE); break;
> case MIPS_USI_FTYPE_VOID: types[(int) type] = build_function_type_list (unsigned_intSI_type_node, void_type_node, NULL_TREE); break;
> That is wrong, because functions which don't take any arguments
> (i.e. (void) or C23/C++ ()) should be using void_list_node as
> TYPE_ARG_TYPES, not a TREE_LIST with void_type_node TREE_VALUE
> and TREE_CHAIN being that void_list_node.  Although void_list_node
> also has TREE_VALUE of void_type_node, various places in the C++
> FE as well as in the middle-end rely on void_list_node to be unique,
> compare it using pointer comparison.
> The following testcase strangely happens to compile fine when compiled
> in C, but fails in C++ (which reports wrong number of arguments due
> to this bug).
> 
> The following simple patch just arranges those 0 argument functions
> to have the MIPS_*_FTYPE_VOID enumerators be named as before, but
> in the build_function_type_list call omit that ", void_type_node" part,
> so it creates correct 0 arguments FUNCTION_TYPE.
> 
> Tested using cross from x86_64-linux to mips, I don't have a setup to
> test this further.  Ok for trunk/16.2?

LGTM.

Richard.

> 2026-07-30  Jakub Jelinek  <[email protected]>
> 
> 	PR target/126484
> 	* config/mips/mips-ftypes.def (MIPS_SI_FTYPE_VOID,
> 	MIPS_USI_FTYPE_VOID): Use DEF_MIPS_FTYPE with 0 as
> 	first argument rather than 1 and leave out ", VOID" from
> 	second argument.
> 	* config/mips/mips.cc (MIPS_FTYPE_NAME0): Define.
> 	(MIPS_FTYPE_ATYPES0): Define.
> 
> 	* g++.target/mips/pr126484.C: New test.
> 
> --- gcc/config/mips/mips-ftypes.def.jj	2026-07-29 23:02:55.847962234 +0200
> +++ gcc/config/mips/mips-ftypes.def	2026-07-30 14:57:37.157545562 +0200
> @@ -75,7 +75,7 @@ DEF_MIPS_FTYPE (1, (SI, V4QI))
>  DEF_MIPS_FTYPE (2, (SI, V4QI, V4QI))
>  DEF_MIPS_FTYPE (2, (SI, V4SI, UQI))
>  DEF_MIPS_FTYPE (2, (SI, V8HI, UQI))
> -DEF_MIPS_FTYPE (1, (SI, VOID))
> +DEF_MIPS_FTYPE (0, (SI))
>  
>  DEF_MIPS_FTYPE (2, (UDI, UDI, UDI))
>  DEF_MIPS_FTYPE (2, (UDI, UV2SI, UV2SI))
> @@ -84,7 +84,7 @@ DEF_MIPS_FTYPE (2, (UDI, V2DI, UQI))
>  DEF_MIPS_FTYPE (2, (USI, V16QI, UQI))
>  DEF_MIPS_FTYPE (2, (USI, V4SI, UQI))
>  DEF_MIPS_FTYPE (2, (USI, V8HI, UQI))
> -DEF_MIPS_FTYPE (1, (USI, VOID))
> +DEF_MIPS_FTYPE (0, (USI))
>  
>  DEF_MIPS_FTYPE (2, (UV16QI, UV16QI, UQI))
>  DEF_MIPS_FTYPE (2, (UV16QI, UV16QI, UV16QI))
> --- gcc/config/mips/mips.cc.jj	2026-07-29 23:02:55.856962123 +0200
> +++ gcc/config/mips/mips.cc	2026-07-30 14:59:58.251806304 +0200
> @@ -211,6 +211,7 @@ enum mips_ucbranch_type
>  };
>  
>  /* Macros to create an enumeration identifier for a function prototype.  */
> +#define MIPS_FTYPE_NAME0(A) MIPS_##A##_FTYPE_VOID
>  #define MIPS_FTYPE_NAME1(A, B) MIPS_##A##_FTYPE_##B
>  #define MIPS_FTYPE_NAME2(A, B, C) MIPS_##A##_FTYPE_##B##_##C
>  #define MIPS_FTYPE_NAME3(A, B, C, D) MIPS_##A##_FTYPE_##B##_##C##_##D
> @@ -17137,6 +17138,9 @@ mips_build_cvpointer_type (void)
>  
>  /* MIPS_FTYPE_ATYPESN takes N MIPS_FTYPES-like type codes and lists
>     their associated MIPS_ATYPEs.  */
> +#define MIPS_FTYPE_ATYPES0(A) \
> +  MIPS_ATYPE_##A
> +
>  #define MIPS_FTYPE_ATYPES1(A, B) \
>    MIPS_ATYPE_##A, MIPS_ATYPE_##B
>  
> --- gcc/testsuite/g++.target/mips/pr126484.C.jj	2026-07-30 15:03:43.880003854 +0200
> +++ gcc/testsuite/g++.target/mips/pr126484.C	2026-07-30 15:04:04.168751854 +0200
> @@ -0,0 +1,8 @@
> +// PR target/126484
> +// { dg-do compile }
> +
> +int
> +foo ()
> +{
> +  return __builtin_mips_get_fcsr ();
> +}
> 
> 	Jakub
> 
> 

-- 
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Jochen Jaser, Andrew McDonald, Abhinav Puri; (HRB 36809, AG Nuernberg)