On 11/23/2015 10:32 AM, David Nadlinger wrote:
This is how the function looks in LDC (on OS X, but the libunwind "client"-side
code is very similar):
---
0000000100000a40 <__D5test24foo1FZv>:
100000a40: 53 push rbx
100000a41: e8 ca fe ff ff call 100000910 <__D4test3abcFZv>
100000a46: e8 d5 fe ff ff call 100000920 <__D4test3defFZv>
100000a4b: 5b pop rbx
100000a4c: e9 ef fe ff ff jmp 100000940 <__D4test3jklFZv>
100000a51: 48 89 c3 mov rbx,rax
100000a54: 83 fa 03 cmp edx,0x3
100000a57: 74 05 je 100000a5e
<__D5test24foo1FZv+0x1e>
100000a59: 83 fa 02 cmp edx,0x2
100000a5c: 75 0f jne 100000a6d
<__D5test24foo1FZv+0x2d>
100000a5e: e8 5d ff 00 00 call 1000109c0 <__d_eh_enter_catch>
100000a63: 48 8b 3b mov rdi,QWORD PTR [rbx]
100000a66: e8 c5 fe ff ff call 100000930
<__D4test3ghiFC4test2CCZv>
100000a6b: eb de jmp 100000a4b
<__D5test24foo1FZv+0xb>
100000a6d: 83 fa 01 cmp edx,0x1
100000a70: 75 10 jne 100000a82
<__D5test24foo1FZv+0x42>
100000a72: e8 49 ff 00 00 call 1000109c0 <__d_eh_enter_catch>
100000a77: e8 d4 fe ff ff call 100000950 <__D4test3mnoFZv>
100000a7c: 5b pop rbx
100000a7d: e9 be fe ff ff jmp 100000940 <__D4test3jklFZv>
100000a82: 48 89 df mov rdi,rbx
100000a85: e8 16 ff 00 00 call 1000109a0 <__d_eh_resume_unwind>
---
The code looks quite good. I've been trying to adjust things, however, so there
are no pushes and pops in the code, trying to preallocate everything needed in
the function prolog.
And why is there a 'default' call to _Unwind_Resume if RDX isn't an expected
value? Shouldn't the personality routine simply not jump to the landing pad if
none of the catch types are satisfied?
The reason LDC emits the __d_eh_resume_unwind call all the time is because it is
needed as soon as there is a cleanup involved anyway, and so far I was just too
lazy to optimize the extra branch away in the special case that there are no
cleanups.
dmd rewrites try-catch-finally into try-{try-catch}-finally, which makes it
easier to generate code, because fewer special cases and fewer bugs. I've become
a big fan of that technique :-)
