Be a little more flexible about Span constructors. #26701
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PR #26701: Size comparison from f55fa96 to 476d041 Increases (22 builds for bl702, cc32xx, esp32, k32w, linux, psoc6)
Decreases (4 builds for bl702, efr32, nrfconnect)
Full report (42 builds for bl602, bl702, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg)
|
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PR #26701: Size comparison from 149b756 to 504a947 Increases (26 builds for bl702, cc32xx, k32w, linux, psoc6, telink)
Decreases (10 builds for bl602, bl702, efr32, k32w, nrfconnect, telink)
Full report (57 builds for bl602, bl702, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
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Before this change, this code:
struct X {
int member;
};
struct Y : public X {
};
Y object;
Span<X> span(&Y, 1);
would not compile, because we had std::is_same checks on the types (X and Y in
this case). But this code is in fact safe as long as sizeof(Y) == sizeof(X), so
we don't get confused about our object boundaries.
This change replaces the std::is_same checks with sizeof() checks. But that
leads to some situations being ambiguous, because the "can this pointer actually
work for us?" check happens after overload resolution, so we explicitly do the
std::is_convertible checks alongside sizeof to make sure that the pointer passed
to our Span constructor will work.
bzbarsky-apple
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PR #26701: Size comparison from bfa0580 to 0cd5f9d Increases (28 builds for bl602, bl702, cc32xx, linux, psoc6, telink)
Decreases (7 builds for bl702, efr32, esp32, telink)
Full report (57 builds for bl602, bl702, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
|
jmartinez-silabs
approved these changes
May 22, 2023
p0fi
approved these changes
May 22, 2023
arkq
approved these changes
May 23, 2023
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Before this change, this code:
would not compile, because we had std::is_same checks on the types (X and Y in this case). But this code is in fact safe as long as sizeof(Y) == sizeof(X), so we don't get confused about our object boundaries.
This change replaces the std::is_same checks with sizeof() checks. But that leads to some situations being ambiguous, because the "can this pointer actually work for us?" check happens after overload resolution, so we explicitly do the std::is_convertible checks alongside sizeof to make sure that the pointer passed to our Span constructor will work.