Sylvestre Ledru [:Sylvestre] Reporter
	Description • 6 years ago

nsTextFrame.cpp:1768, Clang (LLVM based), Priority: Normal
return value of 'GetFirstFontMetrics' is a large (144 bytes) pass-by-value object; pass it by reference instead ?

	Daniel Holbert [:dholbert]
	Comment 1 • 6 years ago

DXR link:
https://dxr.mozilla.org/mozilla-central/rev/085cdfb90903d4985f0de1dc7786522d9fb45596/layout/generic/nsTextFrame.cpp#1766-1774

(We don't benefit from return value optimization here because there are two different possible return values.)

	Xidorn Quan [:xidorn] UTC+11
	Comment 2 • 6 years ago

If having two different possible return values is a problem, can we do something like
> gfxFont::Metrics result;
> if (aFontGroup) {
>   result = ...;
> }
> return result;

I guess a better way would probably be making the empty one a static, and return a reference to it. (Although I would really be surprised if compiler cannot optimize this function out.)