No CTFE of function

[Cecil Ward via Digitalmars-d-learn]

I have a pure function that has constant inputs, known at 
compile-time, contains no funny stuff internally - looked at the 
generated code, and no RTL calls at all. But in a test call with 
constant literal values (arrays initialised to literal) passed to 
the pure routine GDC refuses to CTFE the whole thing, as I would 
expect it (based on previous experience with d and GDC) to simply 
generate a trivial function that puts out a block of 
CTFE-evaluated constant data corresponding to the input.

Unfortunately it's a bit too long to post in here. I've tried 
lots of variations. Function is marked nogc safe pure nothrow

Any ideas as to why GDC might just refuse to do CTFE on 
compile-time-known inputs in a truly pure situation? Haven't 
tried DMD yet. Can try LDC. Am using d.godbolt.org to look at the 
result, as I don't have a machine here to run a d compiler on.

Other things I can think of. Contains function-in-a-function 
calls, which are all unlined out in the generated code nicely, 
and not the first time I've done that with GDC either.

Switches: Am using -Os or -O2 or -O3 - tried all. Tuning to 
presume + enable the latest x86-64 instructions. release build, 
no bounds-checks.