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Home Server Server CPUs The Case For Compilers: A Look at SPEC CPU 2026 on LLVM...
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SPEC CPU2026 Launch STH Cover
Earlier this week marked the introduction of SPEC CPU 2026, the latest iteration of the SPEC consortium’s industry defining CPU benchmark suite. The first new release of SPEC CPU in almost a decade, SPEC CPU 2026 brings with it a significant change to the benchmark applications within the suite, and the types of workloads being run on those applications. With three-quarters of the suite being comprised of new benchmarks – and the last quarter using heavily revised workloads – the release of SPEC CPU 2026 has laid out a new rule set for what the next decade of CPUs will be measured by.
One of the more notable aspects of the benchmark suite is that for reasons of architectural portability and fairness, the suite is distributed as source code rather than pre-compiled binaries. This, in turn, means that the software environment and compiler toolchain the benchmark is built against can have an impact on performance – sometimes significantly so – which is unique for CPU benchmarks. It also means that SPEC CPU 2026 is not purely a hardware benchmark: compilers are a major part of the calculus that goes into the performance figures the benchmarks generate.
And this brings us to today’s article. Because of the long amount of time it takes to complete a representative SPEC CPU 2026 run (upwards of 24 hours), for our initial launch coverage of the benchmark suite’s launch we opted to stick with a safe and well-tested software setup. This meant running versions of the suite compiled on LLVM 20.1.8, the current stable branch of the widely used compiler and toolchain. The trade-off to that, however, is that LLVM 20 itself is nearly a year old; bleeding edge development of LLVM is currently on LLVM 22.
So with a bit more time on our hands, we decided to take a deeper look at SPEC CPU 2026. Given the importance of compilers in the benchmark suite’s performance, just what would the performance impact be by living on the edge and using binaries built with LLVM 22? Today we are going to find out.
The Case for Compilers
As we wrote in our initial SPEC CPU 2026 article, compilers play a critical role in the benchmark.
"The corollary is that, rather uniquely, SPEC CPU is as much a benchmark of compilers as it is of hardware. Because the source code is a fully portable, high-level implementation of a program, and thus contains no CPU intrinsics or other architecture-specific code, the benchmark is at the mercy of a good compiler to turn it into fast, efficient machine code. This means that compiler improvements to boost your SPEC CPU scores are fair game (an especially important aspect for hardware vendors who produce their own compilers), but the catch is that those optimizations cannot be for SPEC alone; they need to benefit a wider class of programs."
This means that as SPEC CPU ages, it is typical to see the performance of the benchmark improve on a given set of hardware. How much performance improves varies greatly from benchmark to benchmark. But as...