Count tail-padding in the size of imported C types. #3937
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This allows us to freely pass the address of a variable of such types to a C function without worrying about it overwriting other things if e.g. it memcpy's sizeof(T) bytes and thus clobbers the otherwise-non-existent tail padding. There are ways to get this optimization back, but they require things like materializing to a temporary instead of passing the address directly. We haven't done that work yet, so we don't get to take advantage of it. rdar://26828018
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@swift-ci Please smoke test. |
| @@ -81,7 +81,7 @@ | |||
| // CHECK-64: ============== | |||
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| // CHECK-64: - __C.MyCStruct: | |||
| // CHECK-64: Size: 17 | |||
| // CHECK-64: Size: 24 | |||
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This needs changes in CHECK-32 mode as well.
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Yeah, I've updated it, thanks.
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What's in this pull request?
Resolved bug number: (SR-)
rdar://26828018
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This allows us to freely pass the address of a variable of such
types to a C function without worrying about it overwriting other
things if e.g. it memcpy's sizeof(T) bytes and thus clobbers the
otherwise-non-existent tail padding.
There are ways to get this optimization back, but they require
things like materializing to a temporary instead of passing the
address directly. We haven't done that work yet, so we don't
get to take advantage of it.
rdar://26828018