62 Benchmarks, 12 Systems, 4 Compilers: Our Most Extensive Benchmarks Yet Of GCC vs. Clang Performance
Written by Michael Larabel in Software on 5 February 2019. Page 1 of 6. 12 Comments

After nearly two weeks of benchmarking, here is a look at our most extensive Linux x86_64 compiler comparison yet between the latest stable and development releases of the GCC and LLVM Clang C/C++ compilers. Tested with GCC 8, GCC 9.0.1 development, LLVM Clang 7.0.1, and LLVM Clang 8.0 SVN were tests on 12 distinct 64-bit systems and a total of 62 benchmarks run on each system with each of the four compilers... Here's a look at this massive data set for seeing the current GCC vs. Clang performance.

With the GCC 9 and Clang 8 releases coming up soon, I've spent the past two weeks running this plethora of compiler benchmarks on a range of new and old, low and high-end systems within the labs. The 12 chosen systems aren't meant for trying to compare the performance between processors but rather a diverse look at how Clang and GCC perform on varying Intel/AMD microarchitectures. For those curious about AArch64 and POWER9 compiler performance, that will come in a separate article with this testing just looking at the Linux x86_64 compiler performance.

The 13 systems tested featured the following processors:

- AMD FX-8370E (Bulldozer)
- AMD A10-7870K (Godavari)
- AMD Ryzen 7 2700X (Zen)
- AMD Ryzen Threadripper 2950X (Zen)
- AMD Ryzen Threadripper 2990WX (Zen)
- AMD EPYC 7601 (Zen)
- Intel Core i5 2500K (Sandy Bridge)
- Intel Core i7 4960X (Ivy Bridge)
- Intel Core i9 7980XE (Skylake X)
- Intel Core i7 8700K (Coffeelake)
- Intel Xeon E5-2687Wv3 (Haswell)
- Intel Xeon Silver 4108 (SP Skylake)

The selection was chosen based upon systems in the server room that weren't pre-occupied with other tests, of interest for a diverse look across several generations of Intel/AMD processors, and obviously based upon the hardware I have available. The storage and RAM varied between the systems, but again the focus isn't for comparing these CPUs rather seeing how GCC 8, GCC 9, Clang 7, and Clang 8 compare. Ubuntu 18.10 was running on these systems with the Linux 4.18 kernel. All of the compiler releases were built in their release/optimized (non-debug) builds. During the benchmarking process on all of the systems, the CFLAGS/CXXFLAGS were maintained of "-O3 -march=native" throughout.

These compiler benchmarks are mostly focused on the raw performance of the resulting binaries but also included a few tests looking at the compile time performance too. For those short on time and wanting a comparison at the macro level, here is an immediate look at the four-way compiler performance across the dozen systems and looking at the geometric mean of all 62 compiler benchmarks carried out in each configuration:

On the AMD side, the Clang vs. GCC performance has reached the stage that in many instances they now deliver similar performance... But in select instances, GCC still was faster: GCC was about 2% faster on the FX-8370E system and just a hair faster on the Threadripper 2990WX but with Clang 8.0 and GCC 9.0 coming just shy of their stable predecessors. These new compiler releases didn't offer any breakthrough performance changes overall for the AMD Bulldozer to Zen processors benchmarked.

On the Intel side, the Core i5 2500K interestingly had slightly better performance on Clang over GCC. With Haswell and Ivy Bridge era systems the GCC vs. Clang performance was the same. With the newer Intel CPUs like the Xeon Silver 4108, Core i7 8700K, and Core i9 7980XE, these newer Intel CPUs were siding with the GCC 8/9 compilers over Clang for a few percent better performance.

Now onward to the interesting individual data points... But before getting to that, if you appreciate all of the Linux benchmarking done day in and day out at Phoronix, consider joining Phoronix Premium to make this testing possible. Phoronix relies primarily on (pay per impression) advertisements to continue publishing content as well as premium subscriptions for those who prefer not seeing ads. Premium gets you ad-free access to the site as well as multi-page articles (like this!) all on a single page, among other benefits. Thanks for your support and at the very least to not be utilizing any ad-blocker on this web-site. Now here is the rest of these 2019 compiler benchmark results.

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