GCC vs. LLVM-GCC Benchmarks

[[Knuckles]]

Couple of factors I would guess comes into play. LLVM is fairly young in development and the biggest improvements so far as performance concerning LLVM is the time to compile. Unfortunately we haven't seen any of those compile times in the tests.

But do normal users really care?

I think compile times should only be used as a test workload when comparing computers; using compile times to benchmark compilers is useless to most people (99%? more?).

[deanjo]

Someone mentioned there could be only one core used when comes to GCC and Ubuntu vs OS X benchmarks. Btw. I heard GCC is optimized to be good at some benchmarks, but I wonder if its better results have reflection in reality.

The way timed compilation tests are written in PTS gcc should take full advantage of the available cores.

For example the apache compile test:

\$TIMER_START
make -s -j \$NUM_CPU_JOBS 2>&1
\$TIMER_STOP" > time-compile-apache

[deanjo]

But do normal users really care?

I think compile times should only be used as a test workload when comparing computers; using compile times to benchmark compilers is useless to most people (99%? more?).

Probably not, but for the most part 99% of users don't care about the delta difference on most of the benchmarks. If it runs, that's good enough for them. The exception being maybe the game benches where even then once your maxing out your monitor's capability everything else is purely for bragging rights.

[kraftman]

The way timed compilation tests are written in PTS gcc should take full advantage of the available cores.

For example the apache compile test:

\$TIMER_START
make -s -j \$NUM_CPU_JOBS 2>&1
\$TIMER_STOP" > time-compile-apache

Yes, I just looked at this

[EnderWiggin]

When building these tests, is there a way to also build and affect the C runtime library. While I can appreciate that many of these tests have "hard stuff" in their code, the performance of an app is always so dependent on the performance of it's underlying runtime library (for things like memcpy, strcmp, etc.) that I think it's worth a look.

[tettamanti]

When building these tests, is there a way to also build and affect the C runtime library.

Hum, probably you can manage to override the system library with LD_PRELOAD (or LD_LIBRARY_PATH).

While I can appreciate that many of these tests have "hard stuff" in their code, the performance of an app is always so dependent on the performance of it's underlying runtime library (for things like memcpy, strcmp, etc.) that I think it's worth a look.

For critical paths (like memcpy, strcmp, ...) the library is probably picking up the most appropriate hand-coded ASM version of the function

[hdante]

I think the description of llvm-gcc is incorrect. llvm-gcc back end is not a modified version of gcc, it's llvm. llvm-gcc front end is a modified version of gcc front end. Please confirm.

And the results were really insightful.

[b15hop]

Do a test of GCC vs Intel compiler and/or any other compiler. Compile time speed, run time speed, code size ... hmm..

[nanonyme]

I wonder how long it takes until Gentoo migrates to clang... Faster compile speed should be crucial there.

[ioannis]

Can you guys do a comparison of modern gcc and llvm with Visual Studio and Intel's compiler? It would be interesting to see where the open source compilers are against the proprietary