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Alyssa Rosenzweig
bd4464bd5e
Instruction count CI has transformed the way we work on FEX… I love the system and want to make it better. there’s one part of instruction count CI that isn’t so lovable: the problematic “optimal” flag on instructions. There are several issues with this flag, both philosophical and practical. – it is tedious to update the optimal flag when making an implementation optimal. The effect of that is discouraging people from making instructions, optimal, or encouraging people to fail to update the flag, and dilute the value of it. Either way, since we care far more about optimal implementations, then we do about updating the flag, clearly we should prioritize the implementation and not the flag. This issue was not obvious at the outset, when instruction count, CI was introduced, and still quite small. The problem magnified when we started duplicating instructions in bulk for different combinations of CPU features (flagm, AFP, etc.) that intern multiplies the manual work required to update the flags by the corresponding constant factor. if it comes down to a choice between removing this extra coverage and removing the flag, I think we all agree that removing the flag is the lesser evil. – The definition of “optimal” is fundamentally problematic. I have often improved the instruction count of an instruction that was already “optimal”. This is all kinds of silly, and calls into question whether there’s any value whatsoever in the existing classifications of the flag. Furthermore, it is often unknowable, whether an implementation really is optimal. Is it possible to implement BZHI (with flag calculations) in fewer than eight instructions? We don’t know, and it’s silly to pretend that we do. – as a consequence of the problematic definitions , there are so many errors in both directions that I don’t think there’s much value in preserving the existing classification at the expense of +progress. Being able to say “32% of instructions are translated optimally” is neat, but it really doesn’t tell us anything whatsoever when you dig a little deeper. So, as the flag is misleading at best and perhaps harmful at worst, let’s remove it and make the instruction count CI, more useful overall. let’s let the expected count and the assembly speak for themselves, and cut away the chaff. if we want a meaningless number to report to management, we can instead calculate the average blowup factor ;-) Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
FEX Unit tests
FEX has its own test suite for x86-64 emulation, and we also use gcc's target tests, posixtest, and gvisor's tests. We use a combination of CMake/CTest and python runner scripts.
We also regularly run and pass qemu's and valgrind's tests for validation, but those aren't in CI right now.
x86/64 testing
- A lot of handwritten assembly unit tests in 32Bit_ASM and ASM folders, run via our TestHarnessHelper
- A few handwritten IR tests in IR, run via our IRLoader
- gcc-target-tests-32 and gcc-target-tests-64, run via FEXLoader. The tests binaries are in External/fex-gcc-target-tests-bins
Syscall testing
- 64-bit posixtest from http://posixtest.sourceforge.net/, run via FEXLoader. The tests binaries are in External/fex-posixtest-bins
- 64-bit gvisor tests from https://github.com/google/gvisor, run via FEXLoader. The tests binaries are in External/fex-gvisor-tests-bins