Hi! The following patch implements the https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3457.htm paper without the first 3 lines in Recommended practice. Seems GCC behavior already matches the expected behavior except for diagnostics of more than 2147483648 __COUNTER__ expansions, so the patch adds a diagnostic for that (but not testcase because #define A __COUNTER__ __COUNTER__ __COUNTER__ __COUNTER__ __COUNTER__ __COUNTER__ __COUNTER__ __COUNTER__ #define B A A A A A A A A #define C B B B B B B B B #define D C C C C C C C C #define E D D D D D D D D #define F E E E E E E E E #define G F F F F F F F F #define H G G G G G G G G #define I H H H H H H H H #define J I I I I I I I I J J J J __COUNTER__ just takes too long to preprocess). Plus I've included all the snippets from the paper into one testcase.
Tested on x86_64-linux, ok for trunk? 2025-09-01 Jakub Jelinek <[email protected]> * macro.cc: Implement C2Y N3457 - The __COUNTER__ predefined macro. (_cpp_builtin_macro_text): Diagnose if __COUNTER__ reaches 2147483648 value. * gcc.dg/cpp/c2y-counter-1.c: New test. --- libcpp/macro.cc.jj 2025-08-15 22:31:17.289081163 +0200 +++ libcpp/macro.cc 2025-09-01 14:42:38.786893989 +0200 @@ -733,6 +733,9 @@ _cpp_builtin_macro_text (cpp_reader *pfi "%<__COUNTER__%> expanded inside directive with " "%<-fdirectives-only%>"); number = pfile->counter++; + if (number == 0x80000000U) + cpp_error (pfile, CPP_DL_ERROR, + "%<__COUNTER__%> expanded more than 2147483648 times"); break; case BT_HAS_ATTRIBUTE: --- gcc/testsuite/gcc.dg/cpp/c2y-counter-1.c.jj 2025-09-01 13:54:35.449359797 +0200 +++ gcc/testsuite/gcc.dg/cpp/c2y-counter-1.c 2025-09-01 14:09:01.743143429 +0200 @@ -0,0 +1,44 @@ +/* N3457 - The __COUNTER__ predefined macro */ +/* { dg-do run } */ +/* { dg-options "-std=c2y -pedantic-errors" } */ + +#ifndef __COUNTER__ +#error "__COUNTER__ not defined" +#endif + +#define A(X) X + X +static_assert (A(__COUNTER__) == 0); +#define B(X) +B(__COUNTER__) +static_assert (__COUNTER__ == 1); +#define C(...) __VA_OPT__() +C(__COUNTER__) +static_assert (__COUNTER__ == 3); +#define D(...) __VA_OPT__(a) +int D(__COUNTER__) = 1; +static_assert (__COUNTER__ == 5); +#define E(X) #X +const char *b = E(__COUNTER__); +#define F(X) a##X +int F(__COUNTER__) = 2; +static_assert (__COUNTER__ == 6); +#define G(X) b##X = X +int G(__COUNTER__); +static_assert (__COUNTER__ == 8); +#if !defined(__COUNTER__) || (__COUNTER__ + 1 != __COUNTER__ + 0) +#error "Unexpected __COUNTER__ behavior") +#endif +static_assert (__COUNTER__ == 11); + +extern int strcmp (const char *, const char *); +extern void abort (); + +int +main () +{ + if (a != 1 + || strcmp (b, "__COUNTER__") + || a__COUNTER__ != 2 + || b__COUNTER__ != 7) + abort (); +} Jakub
