[JIT] ARM64 Fix - Use SetOper instead of ChangeOper to preserve flags

[TIHan]

Description

Resolves #84966

The changes from #84605 resulted in the failing test.

I narrowed down the IL to this:

	ldc.r4		ZERO
	ldc.r4		NAN
	bge.un PASS
	br FAIL

This is an unordered comparison against a float ZERO and float NAN. In the importer, when we see this, the GTF_RELOP_NAN_UN flag gets set on the relop. However, if we decide to later swap the relop, calling ChangeOper will clear this bit which is what resulted in the test failing.

The fix is to use SetOper as it will not clear this flag.

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Issue Details

---

Description

Resolves #84966

The changes from #84605 resulted in the failing test.

I narrowed down the IL to this:

	ldc.r4		ZERO
	ldc.r4		NAN
	bge.un PASS
	br FAIL

This is an unordered comparison against a float ZERO and float NAN. In the importer, when we see this, the GTF_RELOP_NAN_UN flag gets set on the relop. However, if we decide to later swap the relop, calling SetOper will clear this bit which is what resulted in the test failing.

I added gtSwapRelop to take into account the GTF_RELOP_NAN_UN flag to make sure it remains on the relop.

Author:	TIHan
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[TIHan]

/azp run runtime-coreclr jitstress

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Azure Pipelines successfully started running 1 pipeline(s).

[TIHan]

/azp run runtime-coreclr jitstress

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[TIHan]

/azp run runtime-coreclr jitstress

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[TIHan]

@dotnet/jit-contrib This is ready. // cc @jakobbotsch