On Monday, February 20, 2017 12:47:43 berni via Digitalmars-d-learn wrote: > with > > > dmd -inline test.d > > I get > > > test.d(8): Error: function test.foo cannot inline function > > When I remove -inline, it compiles, but seems not to inline. I > cannot tell from this small example, but with the large program, > there is no speed gain. > > It also compiles with -inline when I remove the "if (bar==2)...". > I guess, it's now really inlining, but the function is > ridiculously short...
For better or worse, the whole point of pragma(inline, true) is to produce an error when the compiler fails to inline the function. It doesn't force inlining in any way. So, the fact that it produces an error means that the compiler can't inline that function. And it's not going to inline if you're not using -inline. The reality of the matter is that the inliner in the D frontend needs some serious work. So, it's not going to do a very good job. It's better than nothing, but in comparison to what you'd see with your typical C++ compiler, it just isn't as good. Also, there are a number of compiler bugs that get triggered when both -O and -inline are enabled. So, you're likely better off just using -O for now. Regardless, if performance is your #1 concern, then I would suggest that you compile with ldc and not dmd. dmd is great for fast compilation and therefore it's great for development. However, while it produces decent binaries, and it may very well do certain optimizations better than the gcc or llvm backends do, on the whole, dmd's optimizer really can't compare with those of gcc or llvm. ldc almost always produces a faster binary than dmd does (though it does take longer to compile). - Jonathan M Davis
