[RISC-V] Clean up code gen for floating comparisons

[tomeksowi]

There are ways to generate better code for equals-or-unordered and not-equals-and-ordered. However, there are no IL opcodes for them (ceq.un, beq.un, bne) so these code gens can't happen.

As a bonus, flip the comparison result with one instruction.

Part of #84834, cc @dotnet/samsung

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[risc-vv]

41d470bf is being scheduled for building and testing

GIT: 41d470bf4390b89f83968adb94cd90371be05ecb
REPO: dotnet/runtime
BRANCH: main

Release-build FAILED

buildinfo.json

Compilation failed during core build```

</details>

[risc-vv]

a711137 is being scheduled for building and testing

GIT: a711137381bf85fbcd063a60990604c2f9ffd2e4
REPO: dotnet/runtime
BRANCH: main

Release-build FAILED

buildinfo.json

Compilation failed during core build```

</details>

[tomeksowi]

@dotnet/jit-contrib PTAL

[tannergooding]

There are ways to generate better code for equals-or-unordered and not-equals-and-ordered. However, there are no IL opcodes for them (ceq.un, beq.un, bne) so these code gens can't happen.

IL opcodes aren't required to generate such code. You can recognize patterns such as x == cns or various helpers like T.IsNaN, T.IsFinite, etc.

[risc-vv]

f67b60a is being scheduled for building and testing

GIT: f67b60a9332dff5310247852c613d9661dcbe8d7
REPO: dotnet/runtime
BRANCH: main

Release-build FAILED

buildinfo.json

Cloning into '/godata/pipelines/Release-build/runtime'...
error: RPC failed; curl 92 HTTP/2 stream 5 was not closed cleanly: CANCEL (err 8)
error: 4702 bytes of body are still expected
fetch-pack: unexpected disconnect while reading sideband packet
fatal: early EOF
fatal: fetch-pack: invalid index-pack output

[tomeksowi]

IL opcodes aren't required to generate such code. You can recognize patterns such as x == cns or various helpers like T.IsNaN, T.IsFinite, etc.

True, we can add them when these patterns are recognized and these code gens can be tested.