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[Runtime] Don't write to rodata if values already match. #34616

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Merged
merged 1 commit into from
Nov 10, 2020
Merged

[Runtime] Don't write to rodata if values already match. #34616

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10 changes: 8 additions & 2 deletions stdlib/public/runtime/Metadata.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2721,7 +2721,12 @@ static void initClassFieldOffsetVector(ClassMetadata *self,
// situations where our entire superclass hierarchy is defined
// in Swift. (But note that ObjC might think we have a superclass
// even if Swift doesn't, because of SwiftObject.)
rodata->InstanceStart = size;
//
// The rodata may be in read-only memory if the compiler knows that the size
// it generates is already definitely correct. Don't write to this value
// unless it's necessary.
if (rodata->InstanceStart != size)
rodata->InstanceStart = size;
#endif

// Okay, now do layout.
Expand All @@ -2745,7 +2750,8 @@ static void initClassFieldOffsetVector(ClassMetadata *self,

#if SWIFT_OBJC_INTEROP
// Save the size into the Objective-C metadata as well.
rodata->InstanceSize = size;
if (rodata->InstanceSize != size)
rodata->InstanceSize = size;
#endif
}

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