diff options
Diffstat (limited to 'support/verify.h')
| -rw-r--r-- | support/verify.h | 49 |
1 files changed, 35 insertions, 14 deletions
diff --git a/support/verify.h b/support/verify.h index afdc1ad8..f1097612 100644 --- a/support/verify.h +++ b/support/verify.h @@ -1,6 +1,6 @@ /* Compile-time assert-like macros. - Copyright (C) 2005-2006, 2009-2019 Free Software Foundation, Inc. + Copyright (C) 2005-2006, 2009-2020 Free Software Foundation, Inc. This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by @@ -233,6 +233,22 @@ template <int w> /* @assert.h omit start@ */ +#if 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)) +# define _GL_HAS_BUILTIN_TRAP 1 +#elif defined __has_builtin +# define _GL_HAS_BUILTIN_TRAP __has_builtin (__builtin_trap) +#else +# define _GL_HAS_BUILTIN_TRAP 0 +#endif + +#if 4 < __GNUC__ + (5 <= __GNUC_MINOR__) +# define _GL_HAS_BUILTIN_UNREACHABLE 1 +#elif defined __has_builtin +# define _GL_HAS_BUILTIN_UNREACHABLE __has_builtin (__builtin_unreachable) +#else +# define _GL_HAS_BUILTIN_UNREACHABLE 0 +#endif + /* Each of these macros verifies that its argument R is nonzero. To be portable, R should be an integer constant expression. Unlike assert (R), there is no run-time overhead. @@ -260,24 +276,29 @@ template <int w> # define verify(R) _GL_VERIFY (R, "verify (" #R ")", -) #endif -#ifndef __has_builtin -# define __has_builtin(x) 0 -#endif - /* Assume that R always holds. Behavior is undefined if R is false, - fails to evaluate, or has side effects. Although assuming R can - help a compiler generate better code or diagnostics, performance - can suffer if R uses hard-to-optimize features such as function - calls not inlined by the compiler. */ + fails to evaluate, or has side effects. + + 'assume (R)' is a directive from the programmer telling the + compiler that R is true so the compiler needn't generate code to + test R. This is why 'assume' is in verify.h: it's related to + static checking (in this case, static checking done by the + programmer), not dynamic checking. + + 'assume (R)' can affect compilation of all the code, not just code + that happens to be executed after the assume (R) is "executed". + For example, if the code mistakenly does 'assert (R); assume (R);' + the compiler is entitled to optimize away the 'assert (R)'. + + Although assuming R can help a compiler generate better code or + diagnostics, performance can suffer if R uses hard-to-optimize + features such as function calls not inlined by the compiler. */ -#if (__has_builtin (__builtin_unreachable) \ - || 4 < __GNUC__ + (5 <= __GNUC_MINOR__)) +#if _GL_HAS_BUILTIN_UNREACHABLE # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) #elif 1200 <= _MSC_VER # define assume(R) __assume (R) -#elif ((defined GCC_LINT || defined lint) \ - && (__has_builtin (__builtin_trap) \ - || 3 < __GNUC__ + (3 < __GNUC_MINOR__ + (4 <= __GNUC_PATCHLEVEL__)))) +#elif (defined GCC_LINT || defined lint) && _GL_HAS_BUILTIN_TRAP /* Doing it this way helps various packages when configured with --enable-gcc-warnings, which compiles with -Dlint. It's nicer when 'assume' silences warnings even with older GCCs. */ |