Bug 3490 – DMD Never Inlines Functions that Could Throw

Here's an absurdly simple test program. enforceStuff() does not get inlined, as the disassembly below shows. I couldn't find anything about exceptions in inline.c, but if this doesn't get inlined, I assume nothing that could throw ever does. This severely affects the performance of std.range, since Andrei uses enforce() all over the place, causing lots of stuff not to be inlined. For example, I read disassemblies involving std.range.Take and it seems like Take.popFront() and Take.front() are never inlined. void main() { enforceStuff(1); } void enforceStuff(uint num) { // Not inlined. if(num == 0) { throw new Exception(""); } } Disassembly of main(): __Dmain PROC NEAR ; COMDEF __Dmain push eax ; 0000 _ 50 mov eax, 1 ; 0001 _ B8, 00000001 call _D5test812enforceStuffFkZv ; 0006 _ E8, 00000000(rel) xor eax, eax ; 000B _ 31. C0 pop ecx ; 000D _ 59 ret ; 000E _ C3 __Dmain ENDP

Here's why: int Statement::inlineCost(InlineCostState *ics) { return COST_MAX; // default is we can't inline it } and ThrowStatement never overrides it.

I'm marking this a a blocker of bug 859 so there is a single bug to track all the inlining issues. Please do the same if you open more bugs associated to inlining, or post them directly in bug 859.

undoing false dependency

(In reply to comment #3) > undoing false dependency Can you elaborate a little on why having bug 859 as a tracker of all missing inline oportunities is a bad thing? Thanks

While DMD still doesn't inline functions that (directly) contain a "throw" statement, the original poster's issues with std.range and emplace have largely been addressed several versions ago (at least as far back as 2.060, maybe more): - Many uses of enforce in std.range, such as the ones in Take, have been replaced by asserts. - Functions like Take.popFront() and Take.front() are inlined (likely due to the switch to assert). - Some of the enforce functions (except for errnoEnforce and the enforce that takes a lazy Throwable as a param) are inlineable because they don't use "throw" directly. Instead, they call the private helper "bailOut" which does the actual throwing. The "bailOut" function isn't inlineable, but that shouldn't be a problem since it only gets called when the condition fails.

Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/8f3557c77e524a2b00e4d5c26265041e09318a04 fix issue 3490 - DMD Never Inlines Functions that Could Throw https://github.com/D-Programming-Language/dmd/commit/99b9b04733ba2aa557e09fecdb82650cc56864bd Merge pull request #3378 from Abscissa/fix3490 fix issue 3490 - DMD Never Inlines Functions that Could Throw

I assume this is enough to pay the bounty. @WalterBright?

(In reply to comment #8) > I assume this is enough to pay the bounty. @WalterBright? yes