[RISC-V] Fused multiply-add

[tomeksowi]

Part of #84834, cc @dotnet/samsung

[tomeksowi]

I'm still hesitating whether separating FEATURE_HW_INTRINSICS from SIMD and MASKED_HW_INTRINSICS is the right approach, there's been little code separation between them. Until we bring up the "V" extension the intrinsics RISC-V needs are scalar (e.g. FusedMultiplyAdd, LeadingZeroCount, PopCount, MultiplyHigh) and usually covered in common CoreLib parts like System.Math.

An alternative would be to handle them like #113689 and fix the value numbering for 3-operand GT_INTRINSIC to get FMA:

runtime/src/coreclr/jit/importercalls.cpp

Lines 4312 to 4316 in b21c93c

	// TODO-CQ-XArch: Ideally we would create a GT_INTRINSIC node for fma, however, that currently
	// requires more extensive changes to valuenum to support methods with 3 operands
	// We want to generate a GT_INTRINSIC node in the case the call can't be treated as
	// a target intrinsic so that we can still benefit from CSE and constant folding.

Not sure if changes would be less extensive than maintaining the above mentioned separation.

@dotnet/jit-contrib @jakobbotsch if you have an opinion.

[tomeksowi]

LeadingZeroCount and friends look doable via GT_INTRINSIC (WiP). So that leaves us with FMA as the odd one out.

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[risc-vv]

RISC-V Release-CLR-VF2: 9527 / 9547 (99.79%)

=======================
      passed: 9527
      failed: 3
     skipped: 106
      killed: 17
------------------------
  TOTAL libs: 9653
 TOTAL tests: 9653
   REAL time: 2h 9min 24s 590ms
=======================

Release-CLR-VF2.md, Release-CLR-VF2.xml, testclr_output.tar.gz

Build information and commands

GIT: c2bce30724f34ac65c8d4018925108b3c2c1ae8f
CI: a8426a46d8575dfcb3b5fec0d7d0b7a7c118d690
REPO: tomeksowi/runtime
BRANCH: hw-intrinsics
CONFIG: Release
LIB_CONFIG: Release

RISC-V Release-FX-VF2: 423645 / 458893 (92.32%)

=======================
      passed: 423645
      failed: 678
     skipped: 1482
      killed: 34570
------------------------
  TOTAL libs: 258
 TOTAL tests: 460375
   REAL time: 2h 54min 23s 395ms
=======================

Release-FX-VF2.md, Release-FX-VF2.xml, testfx_output.tar.gz

Build information and commands

GIT: c2bce30724f34ac65c8d4018925108b3c2c1ae8f
CI: a8426a46d8575dfcb3b5fec0d7d0b7a7c118d690
REPO: tomeksowi/runtime
BRANCH: hw-intrinsics
CONFIG: Release
LIB_CONFIG: Release

RISC-V Release-CLR-QEMU: 9527 / 9547 (99.79%)

=======================
      passed: 9527
      failed: 3
     skipped: 106
      killed: 17
------------------------
  TOTAL libs: 9653
 TOTAL tests: 9653
   REAL time: 2h 47min 40s 52ms
=======================

Release-CLR-QEMU.md, Release-CLR-QEMU.xml, testclr_output.tar.gz

Build information and commands

GIT: c2bce30724f34ac65c8d4018925108b3c2c1ae8f
CI: a8426a46d8575dfcb3b5fec0d7d0b7a7c118d690
REPO: tomeksowi/runtime
BRANCH: hw-intrinsics
CONFIG: Release
LIB_CONFIG: Release

RISC-V Release-FX-QEMU: 632088 / 656489 (96.28%)

=======================
      passed: 632088
      failed: 511
     skipped: 1403
      killed: 23890
------------------------
  TOTAL libs: 258
 TOTAL tests: 657892
   REAL time: 1h 55min 8s 138ms
=======================

Release-FX-QEMU.md, Release-FX-QEMU.xml, testfx_output.tar.gz

Build information and commands

GIT: c2bce30724f34ac65c8d4018925108b3c2c1ae8f
CI: a8426a46d8575dfcb3b5fec0d7d0b7a7c118d690
REPO: tomeksowi/runtime
BRANCH: hw-intrinsics
CONFIG: Release
LIB_CONFIG: Release

[am11]

nit: maybe better to define this macro once under #if defined(TARGET_XARCH) || defined (TARGET_ARM64) || defined (TARGET_RISCV64).