Introduce GT_ASSERTION node

[EgorBo]

an alternative for #127117

Diffs

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[Copilot]

Pull request overview

Introduces a new HIR-only IR node (GT_ASSERTION) to seed assertion propagation with “known-true” loop-guard facts (especially after loop inversion), improving the JIT’s ability to eliminate redundant checks inside loops.

Changes:

• Add GT_ASSERTION as a new unary, no-value, not-LIR GenTree operator and plumb it through core visitors/analyses (VN, operand iterators, etc.).
• Insert GT_ASSERTION at the top of the loop body after loop inversion to record the loop guard as true on loop entry.
• Extend assertion propagation to generate one-sided bounds assertions from GT_ASSERTION and ensure GT_ASSERTION statements don’t reach LIR.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/coreclr/jit/gtlist.h	Defines the new GT_ASSERTION node kind and its properties (HIR-only / not LIR).
src/coreclr/jit/optimizer.cpp	Inserts GT_ASSERTION at loop-body entry after loop inversion to seed later optimizations.
src/coreclr/jit/assertionprop.cpp	Generates one-sided bounds assertions from GT_ASSERTION; adds a “no complementary assertion” mode.
src/coreclr/jit/compiler.h	Updates assertion helper signature to support optional complementary assertion creation.
src/coreclr/jit/rationalize.cpp	Drops GT_ASSERTION root statements before converting to LIR (backstop).
src/coreclr/jit/valuenum.cpp	Ensures VN can traverse GT_ASSERTION as a unary node.
src/coreclr/jit/gentree.cpp	Adds GT_ASSERTION support to operand-use iteration utilities.
src/coreclr/jit/compiler.hpp	Adds GT_ASSERTION to operand-use visitation.
src/coreclr/jit/liveness.cpp	Accounts for GT_ASSERTION in LIR liveness/DCE switch handling.
src/coreclr/jit/inductionvariableopts.cpp	Skips GT_ASSERTION statements so they don’t pin IV uses during analysis.

Comments suppressed due to low confidence (1)

src/coreclr/jit/liveness.cpp:2574

• GT_ASSERTION is introduced as a pure marker (no codegen/observable effects), but here it is grouped under LIR nodes that are treated as "always side-effecting" for dead-code elimination. If GT_ASSERTION ever leaks into LIR, this classification will prevent DCE from removing it and makes it more likely to reach Lowering/CodeGen where it isn't supported. Consider treating GT_ASSERTION as removable/no-op in LIR DCE, or asserting it should never appear in LIR.

            case GT_RECORD_ASYNC_RESUME:
            case GT_KEEPALIVE:
            case GT_ASSERTION:
            case GT_SWIFT_ERROR_RET:
            case GT_GCPOLL:
            case GT_WASM_JEXCEPT:
                // Never remove these nodes, as they are always side-effecting.

[EgorBo]

PTAL @jakobbotsch this is the impl you suggested. cc @dotnet/jit-contrib