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QObjectPrivate: use ConnectionList's constructor instead of copy-assignment

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For all new elements, this is the correct thing to do. This seems to
work around an MSVC compiler bug on ARM64. It also seems to generate
better code for x86-64 too, as a nice bonus.

See: https://developercommunity.visualstudio.com/t/codegen-elides-initializers-when-copying/10004323
Before: https://msvc.godbolt.org/z/Wcd4haaPd
After: https://msvc.godbolt.org/z/vWYjazWGr, https://gcc.godbolt.org/z/hdsvTq9nE

Fixes: QTBUG-102246
Change-Id: I29f1c141c0f7436393d9fffd16e2bbbf4c0fe54d
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit bc6087fce259fe600c5d12785fa5f293f129965b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Thiago Macieira 2022-04-04 08:40:43 -07:00 committed by Qt Cherry-pick Bot
parent 2284aa7622
commit dd4b0a3ab9
1 changed files with 4 additions and 1 deletions
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5
src/corelib/kernel/qobject_p.h
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@ -311,11 +311,14 @@ public:
SignalVector *newVector = reinterpret_cast<SignalVector *>(malloc(sizeof(SignalVector) + (size + 1) * sizeof(ConnectionList)));
int start = -1;
if (vector) {
// not (yet) existing trait:
//static_assert(std::is_relocatable_v<SignalVector>);
//static_assert(std::is_relocatable_v<ConnectionList>);
memcpy(newVector, vector, sizeof(SignalVector) + (vector->allocated + 1) * sizeof(ConnectionList));
start = vector->count();
}
for (int i = start; i < int(size); ++i)
newVector->at(i) = ConnectionList();
new (&newVector->at(i)) ConnectionList();
newVector->next = nullptr;
newVector->allocated = size;