Fix incorrect result of complex log/log10/pow on ARM64

[statementreply]

• Perma-workaround bad codegen of vfma_f64 ARM64 intrinsic, using std::fma instead. This also improves codegen (https://godbolt.org/z/7rd4rc3nY).
• Use std::fma for clang on ARM64.
• Drive-by: Fix two lines of comments that are swapped.

Fixes #2857. Fixes DevCom-10088405 and internal VSO-1567425 / AB#1567425 .

I'd appreciate help to run the tests on ARM64 and ARM64EC (especially GH_000935_complex_numerical_accuracy), as I don't have access to an ARM64 Windows machine now.

[strega-nil-ms]

Without changes:

> python out\arm64\tests\utils\stl-lit\stl-lit.py .\tests\std\tests\GH_000935_complex_numerical_accuracy
Testing Time: 72.23s
  Skipped    : 288
  Unsupported: 216
  Failed     :  72

With change:

Testing Time: 85.56s
  Skipped    : 288
  Unsupported: 216
  Passed     :  72

[StephanTLavavej]

Thanks! I've pushed minor changes after validating them on x64 (URL update, preprocessor simplification, extra test coverage).

I'm also looking into testing this on an ARM64 VM - I've requested access which should be granted tomorrow.

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

(I haven't yet gotten ARM64 VM access, but as the existing behavior is already incorrect for ARM64, I'd rather merge this change before the window for 17.4 Preview 2 closes.)

[StephanTLavavej]

I have verified that this works on ARM64:

C:\Users\stl\OneDrive - Microsoft\Documents>set PROCESSOR
PROCESSOR_ARCHITECTURE=ARM64
PROCESSOR_IDENTIFIER=ARMv8 (64-bit) Family 8 Model D0C Revision 301, Ampere(R)
PROCESSOR_LEVEL=3340
PROCESSOR_REVISION=0301

C:\Users\stl\OneDrive - Microsoft\Documents>main.exe
Assertion failed: check_result(result, c), file test.cpp, line 98
abort() has been called
C:\Users\stl\OneDrive - Microsoft\Documents>gh_2870.exe

C:\Users\stl\OneDrive - Microsoft\Documents>

[strega-nil-ms]

@StephanTLavavej did you not see the test I did 😝 ?

[StephanTLavavej]

@strega-nil-ms I totally failed reading comprehension 😹 - didn't see arm64 in the path! Thanks for testing it comprehensively (I tested only one hacked-together configuration manually).

[StephanTLavavej]

Thank you so much for investigating and fixing this runtime correctness bug reported by users!

🐞 ✅ 😻