[mythtv] dynamic_cast generated code

[Mark Spieth]

On 28/01/2020 9:24 am, Peter Bennett wrote:
> Hi Mark
>
> Does this help?
> It calls a function __dynamic_cast and puts the result in sp #120 
> which must be the location of dce. I can't see what __dynamic_cast is 
> doing.
>
> Peter
>
> _the source_
>
> 795 void StandardSettingDialog::customEvent(QEvent *event)
> 796 {
> 797    if (event->type() == DialogCompletionEvent::kEventType)
> 798    {
> 799        auto dce = dynamic_cast<DialogCompletionEvent*>(event);
> 800        if (dce == nullptr)
> 801            return;
>
> _the assembler from -S option_
>
>         .text
>         .globl  _ZN21StandardSettingDialog11customEventEP6QEvent // -- 
> Begin function _ZN21StandardSettingDialog11customEventEP6QEvent
>         .p2align        2
>         .type _ZN21StandardSettingDialog11customEventEP6QEvent, at function
> _ZN21StandardSettingDialog11customEventEP6QEvent: // 
> @_ZN21StandardSettingDialog11customEventEP6QEvent
> .Lfunc_begin167:
>         .loc    68 796 0 is_stmt 1      // standardsettings.cpp:796:0
>         .cfi_startproc
>         .cfi_personality 156, DW.ref.__gxx_personality_v0
>         .cfi_lsda 28, .Lexception51
> // %bb.0:
>         sub     sp, sp, #192            // =192
>         str     x30, [sp, #176]         // 8-byte Folded Spill
>         .cfi_def_cfa_offset 192
>         .cfi_offset w30, -16
>         mrs     x8, TPIDR_EL0
>         ldr     x8, [x8, #40]
>         str     x8, [sp, #168]
>         str     x0, [sp, #136]
>         str     x1, [sp, #128]
>         ldr     x8, [sp, #136]
> .Ltmp2139:
>         .loc    68 797 9 prologue_end   // standardsettings.cpp:797:9
>         ldr     x0, [sp, #128]
>         str     x8, [sp, #72]           // 8-byte Folded Spill
>         .loc    68 797 16 is_stmt 0     // standardsettings.cpp:797:16
>         bl      _ZNK6QEvent4typeEv
>         .loc    68 797 26               // standardsettings.cpp:797:26
>         adrp    x8, :got:_ZN21DialogCompletionEvent10kEventTypeE
>         ldr     x8, [x8, 
> :got_lo12:_ZN21DialogCompletionEvent10kEventTypeE]
>         ldr     w9, [x8]
> .Ltmp2140:
>         .loc    68 797 9                // standardsettings.cpp:797:9
>         subs    w9, w0, w9
>         b.ne    .LBB167_42
>         b       .LBB167_1
> .LBB167_1:
> .Ltmp2141:
>         .loc    68 799 57 is_stmt 1     // standardsettings.cpp:799:57
>         ldr     x8, [sp, #128]
>         mov     x0, x8
>         str     x0, [sp, #64]           // 8-byte Folded Spill
>         .loc    68 799 20 is_stmt 0     // standardsettings.cpp:799:20
>         cbz     x8, .LBB167_3
>         b       .LBB167_2
> .LBB167_2:
>         adrp    x1, :got:_ZTI6QEvent
>         ldr     x1, [x1, :got_lo12:_ZTI6QEvent]
>         adrp    x2, :got:_ZTI21DialogCompletionEvent
>         ldr     x2, [x2, :got_lo12:_ZTI21DialogCompletionEvent]
>         mov     x0, xzr
>         ldr     x3, [sp, #64]           // 8-byte Folded Reload
>         str     x0, [sp, #56]           // 8-byte Folded Spill
>         mov     x0, x3
>         ldr     x3, [sp, #56]           // 8-byte Folded Reload
>         bl      __dynamic_cast
>         str     x0, [sp, #48]           // 8-byte Folded Spill
>         b       .LBB167_4
> .LBB167_3:
>         .loc    68 0 20                 // standardsettings.cpp:0:20
>         mov     x0, xzr
>         str     x0, [sp, #48]           // 8-byte Folded Spill
>         .loc    68 799 20               // standardsettings.cpp:799:20
>         b       .LBB167_4
> .LBB167_4:
>         .loc    68 0 20                 // standardsettings.cpp:0:20
>         ldr     x8, [sp, #48]           // 8-byte Folded Reload
>         .loc    68 799 14               // standardsettings.cpp:799:14
>         str     x8, [sp, #120]
> .Ltmp2142:
>         .loc    68 800 13 is_stmt 1     // standardsettings.cpp:800:13
>         ldr     x8, [sp, #120]
> .Ltmp2143:
>         .loc    68 800 13 is_stmt 0     // standardsettings.cpp:800:13
>         cbnz    x8, .LBB167_6
>         b       .LBB167_5
> .LBB167_5:
> .Ltmp2144:
>
Thats not very enlightening except that it does call it.

Its probably provided in shared-c++.so.

The problem is probably in Qt then and the way it links with our stuff.

Mark

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