On Sunday, 20 October 2013 at 19:42:29 UTC, Walter Bright wrote:
On 10/20/2013 12:23 PM, bearophile wrote:
Walter Bright:
No. But I do know that alloca() causes pessimizations in the
code generation, and it costs many instructions to execute.
Allocating fixed size things on the stack executes zero
instructions.
1) Alloca allows allocating in the parent context, which is
guaranteed to elide copying, without relying on a "sufficiently
smart compiler".
ref E stalloc(E)(ref E mem = *(cast(E*)alloca(E.sizeof)))
{
return mem;
}
2) If only accessing the previous function parameter was
supported(which is just an arbitrary restriction), it would be
sufficient to create a helper-function to implement VLA:s.
3) Your "fixed size stack allocation" could be combined with
alloca also, in which case it likely would be faster still.
