[Issue 9785] New: dmd -inline should inline lambda delegates

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9785

           Summary: dmd -inline should inline lambda delegates
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: hsteoh at quickfur.ath.cx


--- Comment #0 from hsteoh at quickfur.ath.cx 2013-03-22 11:39:35 PDT ---
Code:
------------------------------------------
import std.stdio;

void main() {
        void loop(void delegate(int x) dg) {
                foreach (i; 0..10) {
                        dg(i);
                }
        }

        loop((x) {
                writeln(x);
        });
}
------------------------------------------

Compile with: dmd -O -inline -release -noboundscheck

Here's the disassembly:
------------------------------------------
0000000000454f80 <_Dmain>:
  454f80:       55                      push   %rbp
  454f81:       48 8b ec                mov    %rsp,%rbp
  454f84:       48 83 ec 18             sub    $0x18,%rsp
  454f88:       53                      push   %rbx
  454f89:       48 b9 e8 4f 45 00 00    movabs $0x454fe8,%rcx
  454f90:       00 00 00 
  454f93:       48 31 c0                xor    %rax,%rax
  454f96:       48 89 45 f0             mov    %rax,-0x10(%rbp)
  454f9a:       48 89 4d f8             mov    %rcx,-0x8(%rbp)
  454f9e:       31 db                   xor    %ebx,%ebx
  454fa0:       8b f3                   mov    %ebx,%esi
  454fa2:       48 8b 7d f0             mov    -0x10(%rbp),%rdi
  454fa6:       48 ff 55 f8             rex.W callq *-0x8(%rbp)
  454faa:       ff c3                   inc    %ebx
  454fac:       83 fb 0a                cmp    $0xa,%ebx
  454faf:       72 ef                   jb     454fa0 <_Dmain+0x20>
  454fb1:       31 c0                   xor    %eax,%eax
  454fb3:       5b                      pop    %rbx
  454fb4:       48 8b e5                mov    %rbp,%rsp
  454fb7:       5d                      pop    %rbp
  454fb8:       c3                      retq   
  454fb9:       90                      nop
  454fba:       90                      nop
  454fbb:       90                      nop

0000000000454fbc <_D4test4mainFZv4loopMFDFiZvZv>:
  454fbc:       55                      push   %rbp
  454fbd:       48 8b ec                mov    %rsp,%rbp
  454fc0:       48 83 ec 28             sub    $0x28,%rsp
  454fc4:       53                      push   %rbx
  454fc5:       48 89 75 f0             mov    %rsi,-0x10(%rbp)
  454fc9:       48 89 55 f8             mov    %rdx,-0x8(%rbp)
  454fcd:       31 db                   xor    %ebx,%ebx
  454fcf:       8b f3                   mov    %ebx,%esi
  454fd1:       48 8b 7d f0             mov    -0x10(%rbp),%rdi
  454fd5:       48 ff 55 f8             rex.W callq *-0x8(%rbp)
  454fd9:       ff c3                   inc    %ebx
  454fdb:       83 fb 0a                cmp    $0xa,%ebx
  454fde:       72 ef                   jb     454fcf
<_D4test4mainFZv4loopMFDFiZvZv+0x13>
  454fe0:       5b                      pop    %rbx
  454fe1:       48 8b e5                mov    %rbp,%rsp
  454fe4:       5d                      pop    %rbp
  454fe5:       c3                      retq   
  454fe6:       90                      nop
  454fe7:       90                      nop

0000000000454fe8 <_D4test4mainFZv16__T9__lambda2TiZ9__lambda2MFiZv>:
  454fe8:       55                      push   %rbp
  454fe9:       48 8b ec                mov    %rsp,%rbp
  454fec:       48 83 ec 10             sub    $0x10,%rsp
  454ff0:       48 89 f2                mov    %rsi,%rdx
  454ff3:       be 0a 00 00 00          mov    $0xa,%esi
  454ff8:       48 bf 00 af 6c 00 00    movabs $0x6caf00,%rdi
  454fff:       00 00 00 
  455002:       e8 59 02 00 00          callq  455260
<_D3std5stdio4File14__T5writeTiTaZ5writeMFiaZv>
  455007:       48 8b e5                mov    %rbp,%rsp
  45500a:       5d                      pop    %rbp
  45500b:       c3                      retq   
------------------------------------------

There are two enhancements (optimizations) possible here:

1) Since loop() is inside main(), and there are no escaping references to it,
it can't possibly be called from anywhere else. Since it's already inlined in
main, there is no point in emitting the function body as a separate function.
So the function body should be omitted.

2) Since the lambda delegate body is known at compile-time, and this is the
only place it's used, the lambda should be inlined as well. Currently it's not
(main still takes the address of the lambda and calls it from the inlined
loop).

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