Bug 14498 – Poor codegen optimization for ranges

dmd and gdc do _very_ poorly on a benchmark featuring D due to what I assume is poor codegen. https://github.com/logicchains/LPATHBench/blob/master/d.d using the "slow"(aka ranges) version, DMD produces code that is 4 times slower. Almost same exact ratios for GDC, so I assume it's due to frontend(?) LDC seems to optimize it away to almost identical performance between "fast" and "slow" version, unsure if it's due to the LLVM optimizations or one of their patches to dmd. dmd 2.067 GC summary for fast version: Number of collections: 1 Total GC prep time: 0 milliseconds Total mark time: 0 milliseconds Total sweep time: 0 milliseconds Total page recovery time: 0 milliseconds Max Pause Time: 0 milliseconds Grand total GC time: 0 milliseconds GC summary: 1 MB, 1 GC 0 ms, Pauses 0 ms < 0 ms dmd 2.067 GC summary for range version: Number of collections: 2711 Total GC prep time: 13 milliseconds Total mark time: 67 milliseconds Total sweep time: 370 milliseconds Total page recovery time: 75 milliseconds Max Pause Time: 0 milliseconds Grand total GC time: 526 milliseconds GC summary: 1 MB, 2711 GC 526 ms, Pauses 80 ms < 0 ms second number is runtime in ms, optimization flags relevant to compilers are enabled. ./dmd_slow 8981 LANGUAGE D 7311 ./dmd_fast 8981 LANGUAGE D 1835 ./gdc_slow 8981 LANGUAGE D 4249 ./gdc_fast 8981 LANGUAGE D 903 ./ldc_slow 8981 LANGUAGE D 999 ./ldc_fast 8981 LANGUAGE D 1078 I marked this as a DMD issue due to LDC producing an expected output despite it being related to phobos.

Upon closer inspection, I believe this is an inlining issue, possibly related to cross-module inlining. If I move the function to another file, LDC achieves similar performance as GDC - but it goes away with singleobj flag. this kills range performance. coincidentally, on arch linux LDC is the only compiler that doesn't use a statically linked phobos. Maybe related?

(In reply to weaselcat from comment #0) > using the "slow"(aka ranges) version, DMD produces code that is 4 times > slower. Almost same exact ratios for GDC, so I assume it's due to frontend(?) > > LDC seems to optimize it away to almost identical performance between "fast" > and "slow" version, unsure if it's due to the LLVM optimizations or one of > their patches to dmd. > AFAIK slow version allocates a closure on the heap, perhaps LDC optimizes out unnecessary closures.

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