Remove an unnecessary switch from GenTree:TryGetUse

[tannergooding]

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[Copilot]

Pull request overview

This PR refactors GenTree::TryGetUse to avoid a large opcode switch by leveraging existing operator classification helpers (OperIsLeaf, OperIsSpecial, unary/binary handling). As part of enabling that simplification, it reclassifies the ARM64 GT_SELECT_{INC,INV,NEG} nodes to be true conditional/special nodes.

Changes:

• Reclassify ARM64 GT_SELECT_{INC,INV,NEG} as GenTreeConditional / GTK_SPECIAL (instead of binary GenTreeOp).
• Add an instance GenTree::OperIsSpecial() convenience helper in gentree.h.
• Rewrite GenTree::TryGetUse to use leaf/special classification and a unified unary/binary path; remove the TryGetUseBinOp helper.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/coreclr/jit/gtlist.h	Changes GT_SELECT_{INC,INV,NEG} node flavor/kind to be conditional/special.
src/coreclr/jit/gentree.h	Adds instance OperIsSpecial(); removes now-unneeded TryGetUseBinOp declaration.
src/coreclr/jit/gentree.cpp	Simplifies GenTree::TryGetUse logic and eliminates the dedicated binop helper.

[tannergooding]

CC. @dotnet/jit-contrib, @EgorBo, @kg for review. Just a simple PR that cleans up GenTree::TryGetUse to use the existing categories.

I found that some of the Arm64 specific conditional nodes were incorrectly tagged as part of this (gtlist and gtstruct didn't agree) and then there was a couple node kinds that were missing from the table so they could've hit the binary path when they shouldn't, so this reduces risk.

Provides a small TP increase as well, more so on LLVM than MSVC:

linux x64
* Overall (-0.02% to -0.00%)
* MinOpts (-0.01% to -0.00%)
* FullOpts (-0.03% to -0.00%)

linux arm64
* Overall (-0.01% to -0.00%)
* FullOpts (-0.01% to -0.00%)

windows x64
* Overall (-0.01% to -0.00%)
* MinOpts (-0.01% to -0.00%)
* FullOpts (-0.01% to -0.00%)

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[kg]

LGTM