More precise range assertions for GT_CNS_INT

[adamperlin]

Fixes #121400; We can use a simple binary search approach to narrow the upper bound for GT_CNS_INT type nodes in assertionprop. Credit for the approach to the comment here: #120980 (comment)

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[Copilot]

Pull request overview

This PR refines the range computation for integral constant nodes (GT_CNS_INT/GT_CNS_LNG) in JIT assertion propagation by selecting a narrower rangeType based on the constant’s magnitude, enabling tighter derived non-negative range assertions.

Changes:

• Replace coarse FitsIn<int32_t>/FitsIn<uint32_t> range typing with a more granular threshold-based selection (8/16/32-bit signed/unsigned) for constants.
• Use the selected narrower type’s maximum to tighten the inferred upper bound when the constant is known non-negative.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/coreclr/jit/assertionprop.cpp:346

• The GT_CNS_INT/GT_CNS_LNG switch case no longer returns or breaks after computing rangeType. This causes an unintended fallthrough into case GT_QMARK, where node->AsQmark() will be called on a constant node (invalid cast / potential crash). Add the missing return (or a break plus an appropriate return) after selecting the tighter rangeType.

        }

        case GT_QMARK:
            return Union(ForNode(node->AsQmark()->ThenNode(), compiler),
                         ForNode(node->AsQmark()->ElseNode(), compiler));