Bug 5788 – Better optimize [] (empty dynamic array literals)

A little D2 program: int[] foo() { return []; } int[] bar() { return null; } void main() {} The asm of the two functions, compiling it with DMD 2.052: dmd -O -release -inline test2.d _D5test23fooFZAi comdat L0: push EAX mov EAX,offset FLAT:_D11TypeInfo_Ai6__initZ push 0 push EAX call near ptr __d_arrayliteralT mov EDX,EAX add ESP,8 pop ECX xor EAX,EAX ret _D5test23barFZAi comdat xor EAX,EAX xor EDX,EDX ret I am not sure, but I think it's better to compile foo() to the same assembly as bar().

No! Often it is extremely useful to distinguish an empty array from a null one. (You do that with "is null"). "Fixing" this will break a lot of my code.

Erm, never mind, [] still creates a null array. I just remembered I had to do something more tricky in my code to make empty non-null arrays. https://github.com/CyberShadow/RABCDAsm/blob/cecff913/abcfile.d#L1094

currently this code: void main() { int[] emptyArray = []; } Produces: __Dmain comdat L0: push EAX mov EAX,offset FLAT:_D11TypeInfo_Ai6__initZ push 0 push EAX call near ptr __d_arrayliteralTX add ESP,8 xor EAX,EAX pop ECX ret

Still here with DMD 2.080: 0000000000000000 <_D4dbug3fooFZAi>: 0: 55 push %rbp 1: 48 8b ec mov %rsp,%rbp 4: 31 f6 xor %esi,%esi 6: 48 8b 3d 00 00 00 00 mov 0x0(%rip),%rdi # d <_D4dbug3fooFZAi+0xd> d: e8 00 00 00 00 callq 12 <_D4dbug3fooFZAi+0x12> 12: 48 89 c2 mov %rax,%rdx 15: 31 c0 xor %eax,%eax 17: 5d pop %rbp 18: c3 retq 19: 00 00 add %al,(%rax) ... Disassembly of section .text._D4dbug3barFZAi: 0000000000000000 <_D4dbug3barFZAi>: 0: 55 push %rbp 1: 48 8b ec mov %rsp,%rbp 4: 31 c0 xor %eax,%eax 6: 31 d2 xor %edx,%edx 8: 5d pop %rbp 9: c3 retq ...

This has been fixed *** This issue has been marked as a duplicate of issue 22922 ***