Linked by ebasconp on Fri 10th Jun 2011 22:22 UTC
Benchmarks "Google has released a research paper that suggests C++ is the best-performing programming language in the market. The internet giant implemented a compact algorithm in four languages - C++, Java, Scala and its own programming language Go - and then benchmarked results to find 'factors of difference'."
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RE[4]: GCC isn't all that great
by Alfman on Mon 13th Jun 2011 19:12 UTC in reply to "RE[3]: GCC isn't all that great"
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"That code can not be vectorised as it is written as 'a' and 'b' may point to overlapping areas of memory.

The 'restrict' keyword is necessary."

Wow, thanks burnttoys, you are correct, some constructive criticism!

It should be using restrict just like 'memcpy' does.

Unfortunately I tried it and it didn't change the output at all. Additionally I see a lot of devs claiming that the restrict keyword doesn't have any effect under GCC, can you confirm that?

Reply Parent Score: 2

burnttoys Member since:

I couldn't tell you more about GCC vectorisation in any great detail.

I have seen restrict et al work (that is generate vector code) on ARM for the NEON instruction set but right now I can't remember if that was RVCT or GCC. If ARM is your thing it might be worth checking the builds of GCC. For x86 - I'm afraid I've no idea. I just hit "build" in Qt Creator as none of my x86 code is really that performance critical anymore!

Reply Parent Score: 1

Alfman Member since:


There seem to have been a small army of devs reporting issues with 'restrict' since 2002, which have been marked as dups of each other. They ultimately point to this bug which indicates a fix in GCC 4.5.

Reply Parent Score: 2