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capisce13y ago· 2 in thread

Which is indicative of performance.

But isn't GCC still written mostly in C? So would not both gcc versions be expected to be very similar on instruction level?

masklinn13y ago

> So would not both gcc versions be expected to be very similar on instruction level?

It's going to go through the g++ frontend, parsing and compiling it using C++ semantics. There's no guarantee that the C subset of C++ will yield the exact same result as that of an actual C compiler. And a decade or two ago, as TFA notes, it most definitely did not.

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RustyRussell13y ago· 1 in thread

Yeah, people seem confused by this. You can build the last release of gcc either with a C++ compiler or with a C compiler. I did both, and benchmarked the results.

Hope that helps! Rusty.

adamnemecekOP13y ago

Sorry, I missed the sentence: "With this in mind, and Ian Taylor’s bold assertion that "The C subset of C++ is as efficient as C", I wanted to test what had changed with some actual measurements."

caf13y ago

It's measuring the speed of the GCC-compiled-as-C compiler against the GCC-compiled-as-C++ compiler by measuring how long each of those takes to compile the Linux kernel. It's not measuring how long it took to compile GCC itself.

masklinn13y ago

To test a compiler's performances, you use it to compile stuff don't you? That's what TFA does: it builds GCC 4.7 using both a C compiler and a C++ compiler, then looks how the results perform, by compiling stuff with them.

TFA did not bench how long the original compilation (whether through C or through C++) took, that would have been pointless and irrelevant.

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