On 15.07.2016 22:29, Walter Bright wrote:
On 7/15/2016 12:55 PM, Jack Stouffer wrote:
On Friday, 15 July 2016 at 19:06:15 UTC, Walter Bright wrote:
4. making use of asserts to provide information to the optimizer
Do dmd/ldc/gdc actually do this?
dmd doesn't. I don't know about other compilers.
The point is it's possible because C++ doesn't have asserts. C++ has an
assert macro, defined to be the same as in C. The definition of assert
in C is such that it is turned on/off with the NDEBUG macro, meaning
that when it is off, the compiler CANNOT derive any semantic information
from it, because it effectively vanishes from the code.
In contrast, assert in D is a keyword and has a semantic production.
Even if generating code for the assert is disabled with the -release
switch, the semantics of it remain and are available to the optimizer.
C++ didn't repeat that mistake with 'static_assert' (another feature
copied from D), but static assert doesn't help the optimizer.
Just to be explicit about this: What kind of "help" do you want to be
provided to the optimizer?
I.e., why didn't you say: "Failing assertions are undefined behavior
with the -release switch."
