diff options
Diffstat (limited to 'gnulib/import/verify.h')
| -rw-r--r-- | gnulib/import/verify.h | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/gnulib/import/verify.h b/gnulib/import/verify.h index d9ab89a570c..f1097612704 100644 --- a/gnulib/import/verify.h +++ b/gnulib/import/verify.h @@ -277,10 +277,22 @@ template <int w> #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 _GL_HAS_BUILTIN_UNREACHABLE # define assume(R) ((R) ? (void) 0 : __builtin_unreachable ()) |