On Tuesday, 18 August 2015 at 10:45:49 UTC, Walter Bright wrote:
So if you're comparing code generated by dmd/gdc/ldc, and
notice something that dmd could do better at (1, 2 or 3),
please let me know. Often this sort of thing is low hanging
fruit that is fairly easily inserted into the back end.
Hi,
From my experience reducing regressions, I have noticed that
backend changes in general have a very high chance of introducing
code generation regressions. Codegen bugs are nasty: they are
occasionally difficult to reduce, and since software is rarely
tested with its "release" build, have a habit of sneaking into
published releases of otherwise bug-free software.
IIRC, I have had three releases affected by optimization/inlining
DMD bugs (two of Digger and one of RABCDAsm). These do not speak
well for D when end-users ask me what the cause of the bug is,
and I have to say "Yeah, it's a bug in the official D compiler".
I think stability of the DMD backend is a goal of much higher
value than the performance of the code it emits. DMD is never
going to match the code generation quality of LLVM and GCC, which
have had many, many man-years invested in them. Working on DMD
optimizations is essentially duplicating this work, and IMHO I
think it's not only a waste of time, but harmful to D because of
the risk of regressions.
I suggest that we revamp the compiler download page again. The
lead should be a "select your compiler" which lists the
advantages and disadvantages of each of DMD, LDC and GDC.
