Fold comparisons into single-value ranges in GetRangeFromAssertions

[EgorBo]

This PR does:

1. More precise Range for VNF_Cast. previously it was whatever CastTo provided, now it also inspects the CastOp (and if its Range is within or smaller than CastTo - use that).
2. More precise Range for relops (e.g. VNF_GT). Previously it was always [0..1], now it tries to fold it to [0..0] (always false) or [1..1] (always true)
3. Improved RangeOps::EvalRelop for GT_EQ/GT_NE operators when ranges are single-value constants.
4. Small cleanups, TP-oriented changes.

Diffs

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[Copilot]

Pull request overview

This PR refines range analysis and assertion propagation so that relational comparisons can often be recognized as always-true or always-false, allowing more branches to be folded.

Changes:

• Extend Range/RangeOps to represent and compute the result of relational operators as [0..0], [1..1], or [0..1] ranges, including improved handling of EQ/NE when operand ranges are disjoint or equal singletons.
• Enhance RangeCheck::GetRangeFromAssertions to use GetRangeFromType, refine cast ranges using the source expression’s range, and to interpret comparison VNFs via RangeOps::EvalRelop, with an early-exit when a single constant value is determined.
• Update optAssertionPropGlobal_RelOp to use range information for the entire relop VN (instead of separate operand ranges) and fold comparisons directly when their range is a single constant 0 or 1.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/jit/rangecheck.h	Adds Range::IsSingleValueConstant and changes RangeOps::EvalRelop to return a Range capturing 0/1 semantics instead of a tri-state enum; RangeCheck::GetRangeFromType is made static.
src/coreclr/jit/rangecheck.cpp	Refactors GetRangeFromAssertions to use GetRangeFromType for casts, use EvalRelop for VN comparison functions, early-return for single-value ranges, and slightly restructures the reaching-assertions visitor.
src/coreclr/jit/assertionprop.cpp	Switches global relop assertion propagation to query the range of the relop’s value number and fold to true/false when the computed range is a single constant 0 or 1.

[EgorBo]

PTAL @jakobbotsch @dotnet/jit-contrib the last piece for now. Diffs

CI was green once, now it's mostly deadlettering.

[hez2010]

It seems that this also mixed some regressions for example the bound check in Microsoft.CodeAnalysis.LittleEndianReader:ReadUInt32 is no longer being folded away?

[EgorBo]

/ba-g deadletter