Handle FMA on RISC-V

[hrw]

MathCore, Matrix tests fail on RISC-V:

266 - gtest-math-mathcore-stressMathCoreUnit (Failed)

Discrepancy in PtEtaPhiMVector operations() :
62919.12458590859 != 62919.124585843325 discr = 5 (Allowed discrepancy is 1.7763568394002505e-13)

300 - gtest-math-matrix-testMatrixTSparse (Failed)

Expected equality of these values:
m1
Which is: 80-byte object <90-0A 9E-93 FF-FF 00-00 00-00 00-00 00-00 00-02 04-00 00-00 05-00 00-00 01-00 00-00 00-00 00-00 14-00 00-00 05-00 00-00 00-00 00-00 00-00 B0-3C 01-E2 1E-94 FF-FF 00-00 30-26 61-55 55-55 00-00 00-62 60-55 55-55 00-00 A0-2B 61-55 55-55 00-00>
m2
Which is: 264-byte object <48-76 56-55 55-55 00-00 00-00 00-00 00-00 00-02 04-00 00-00 05-00 00-00 01-00 00-00 00-00 00-00 14-00 00-00 00-00 00-00 00-00 00-00 00-00 B0-3C 01-00 00-00 03-00 00-00 18-2D 44-54 FB-21 09-40 ... 53-B7 49-9E A1-B8 34-40 40-42 AC-EF 82-70 37-40 E0-09 61-55 55-55 00-00 60-E2 1E-94 FF-FF 00-00 50-2A 61-55 55-55 00-00 20-0A 61-55 55-55 00-00 30-E3 1E-94 FF-FF 00-00 60-E1 1E-94 FF-FF 00-00>

422 - test-stressmathcore (Failed) longtest

Based on my experience with similar failures on AArch64 (years ago) I suspected FMA handling. Looked through code and found some places where disabling/handling FMA was needed.

This Pull request:

Changes or fixes:

It is an attempt to get 'root' build properly on RISC-V. Or at least to get some of tests to pass (we still have a list of tests to skip).

Checklist:

• tested changes locally
• updated the docs (if necessary)

[hrw]

We have build on RISC-V koji: https://riscv-koji.fedoraproject.org/koji/taskinfo?taskID=256015

The list of skipped tests:

%ifarch riscv64
# - gtest-io-io-RIoUring
# - gtest-net-net-testParallelMergingFile
# - gtest-tree-ntuple-ntuple-attributes
# - gtest-tree-ntuplebrowse-ntuple-browse
#   Error initializing io_uring: Function not implemented
#
# - gtest-roofit-roofitcore-testRooFitCore
#   Received unexpected diagnostic of severity 4000 at
#   'TUnixSystem::DispatchSignals' reading 'segmentation violation'.
#
# - gtest-roofit-roofitcore-testNaNPacker
# - gtest-roofit-roofitcore-testLikelihoodGradientJob
#   According to the RISC-V ISA specification, the hardware FPU automatically
#   canonicalizes the result of any floating-point operation that yields a NaN
#   into a standard canonical NaN (`0x7ff8000000000000`). This process
#   permanently clears any custom payload bits stored in the mantissa, causing
#   software that relies on bit-preserving NaN manipulation—such as ROOT's
#   `RooNaNPacker`—to fail on arithmetic tests.
excluded="${excluded}|\
gtest-io-io-RIoUring|\
gtest-net-net-testParallelMergingFile|\
gtest-tree-ntuple-ntuple-attributes|\
gtest-tree-ntuplebrowse-ntuple-browse|\
gtest-roofit-roofitcore-testRooFitCore|\
gtest-roofit-roofitcore-testLikelihoodGradientJob|\
gtest-roofit-roofitcore-testNaNPacker"
%endif

[github-actions]

Test Results

     4 files       4 suites   12h 45m 58s ⏱️
 3 777 tests  3 771 ✅ 6 💤 0 ❌
14 764 runs  14 764 ✅ 0 💤 0 ❌

Results for commit ede5ce9.

[hrw]

My work on it will wait for some fast risc-v hardware. At the moment it takes far too much time to rebuild/test it.