Remove FEATURE_BASICFREEZE

[EgorBo]

FEATURE_BASICFREEZE has been unconditionally defined in every shipping configuration for years:

• CoreCLR — src/coreclr/clrdefinitions.cmake
• NativeAOT — src/coreclr/nativeaot/Runtime/CMakeLists.txt
• standalone clrgc (built inside the CoreCLR tree)

The only in-repo consumer that compiled the disabled path was the GC sample (src/coreclr/gc/sample), which builds the shared GC sources without CoreCLR's global defines (its add_subdirectory(gc/sample) precedes include(clrdefinitions.cmake)).

This removes the FEATURE_BASICFREEZE symbol entirely, making read-only / frozen segment support unconditional. The enabled code path is unchanged — only the dead #else / #ifndef branches are dropped. Combined conditions are simplified, e.g. #if defined(FEATURE_BASICFREEZE) && !defined(USE_REGIONS) → #ifndef USE_REGIONS.

Validation

Built on windows-x64 (Checked) with 0 errors / 0 warnings:

• coreclr.dll (VM + GC)
• clrgc.dll / clrgcexp.dll (standalone GC)
• gcsample.exe — the consumer that previously compiled the removed #else branches; now compiles the frozen-segment code unconditionally
• NativeAOT Runtime.WorkstationGC / Runtime.ServerGC

[dotnet-policy-service]

Tagging subscribers to this area: @anicka-net, @dotnet/gc
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[Copilot]

Pull request overview

This PR removes the FEATURE_BASICFREEZE compile-time symbol from CoreCLR and NativeAOT and makes the “frozen/read-only segment” support code paths unconditional, deleting the now-dead #else branches and simplifying related preprocessor conditions.

Changes:

• Drops FEATURE_BASICFREEZE feature-guarded branches across VM + GC, leaving the already-enabled behavior as the only behavior.
• Makes frozen-segment QCall entrypoints and registrations unconditional (CoreCLR + NativeAOT).
• Removes FEATURE_BASICFREEZE from build definition inputs (CoreCLR cmake + NativeAOT cmake + VS Code IntelliSense defines).

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreclr/vm/syncblk.cpp	Removes dead assertion/return path for frozen-bit validation when basicfreeze was “off”.
src/coreclr/vm/qcallentrypoints.cpp	Makes frozen-segment QCall exports unconditional in the QCall table.
src/coreclr/vm/frozenobjectheap.cpp	Removes the “GC lacks frozen support” early-return branch; allocation now always uses frozen-segment path.
src/coreclr/vm/comutilnative.h	Makes QCall declarations for frozen segment registration unconditional.
src/coreclr/vm/comutilnative.cpp	Makes QCall implementations for frozen segment registration unconditional.
src/coreclr/vm/.vscode/c_cpp_properties.json	Removes FEATURE_BASICFREEZE from IntelliSense defines list.
src/coreclr/nativeaot/Runtime/GCHelpers.cpp	Removes conditional stub return; always registers frozen segments via GC heap.
src/coreclr/nativeaot/Runtime/CMakeLists.txt	Stops defining FEATURE_BASICFREEZE for NativeAOT runtime build.
src/coreclr/gc/sweep.cpp	Removes feature-guard around read-only segment sweeping helpers.
src/coreclr/gc/relocate_compact.cpp	Simplifies readonly-segment check for LOH relocation logic.
src/coreclr/gc/regions_segments.cpp	Removes feature-guards around RO segment mapping/insert/remove support.
src/coreclr/gc/plan_phase.cpp	Makes sweep_ro_segments() unconditional (as it already was in shipping configs).
src/coreclr/gc/mark_phase.cpp	Removes feature-guards around RO segment mark/clear helpers and in-range RO marking (still gated by USE_REGIONS).
src/coreclr/gc/interface.cpp	Simplifies feature-conditional initialization / range checks for frozen segments.
src/coreclr/gc/gcpriv.h	Makes RO-segment-related members/methods unconditional in the GC heap class declaration.
src/coreclr/gc/gcinternal.h	Makes sorted_table, RO-segment range assertions, and lookup prototype unconditional.
src/coreclr/gc/gcinterface.h	Updates interface comment block to remove feature-guard wording.
src/coreclr/gc/gcee.cpp	Makes Register/Unregister/IsIn/UpdateFrozenSegment implementations unconditional.
src/coreclr/gc/gc.cpp	Makes RO segment table storage and lookup support unconditional.
src/coreclr/gc/diagnostics.cpp	Makes RO-segment walking helper unconditional.
src/coreclr/gc/collect.cpp	Makes seg_table->delete_old_slots() unconditional (as per always-enabled feature).
src/coreclr/gc/background.cpp	Makes RO-segment marking/sweeping calls unconditional (still respects USE_REGIONS guards where applicable).
src/coreclr/clrdefinitions.cmake	Stops defining FEATURE_BASICFREEZE for CoreCLR builds.

[github-actions]

Copilot Code Review

Holistic Assessment

Motivation: Justified. FEATURE_BASICFREEZE has been unconditionally defined in every shipping configuration (CoreCLR, NativeAOT) for years. Removing always-true preprocessor guards and their dead #else branches is a clear improvement to code readability and maintainability.

Approach: Correct. The PR mechanically removes the symbol definition from build files, drops all #ifdef/#ifndef guards (keeping the enabled path), removes dead #else branches, and simplifies compound conditions. The removal is complete — grep confirms zero remaining references to FEATURE_BASICFREEZE across the repo.

Summary: ✅ LGTM. This is a clean, mechanical dead-code removal with no behavioral changes to any shipping configuration. The enabled code paths are entirely unchanged. The simplification of compound conditions (e.g., #if defined(FEATURE_BASICFREEZE) && !defined(USE_REGIONS) → #ifndef USE_REGIONS) is correct. The 23 changed files all follow the same straightforward pattern.

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Detailed Findings

Detailed Findings

✅ Complete removal — no remaining references

Verified via repo-wide grep that no references to FEATURE_BASICFREEZE remain in any file (cmake, C++, JSON, headers). The removal is thorough.

✅ Compound condition simplification is correct

All compound conditions were correctly simplified:

• #if defined(FEATURE_BASICFREEZE) && !defined(USE_REGIONS) → #ifndef USE_REGIONS
• #if defined(STRESS_REGIONS) && defined(FEATURE_BASICFREEZE) → #ifdef STRESS_REGIONS
• #if defined(FEATURE_BASICFREEZE) && defined(USE_REGIONS) → #ifdef USE_REGIONS

✅ Dead #else branches correctly removed

The removed #else branches in gcee.cpp, frozenobjectheap.cpp, interface.cpp, GCHelpers.cpp, syncblk.cpp, and gcinternal.h all contained either:

• Unreachable assertions (assert(!"Should not call...")
• Hardcoded false returns (return false, return nullptr, return NULL)
• Weaker assertions without the frozen-segment check

These are the expected dead-code patterns for an always-enabled feature flag.

✅ Functional code preserved unchanged

The enabled code paths (RegisterFrozenSegment, UnregisterFrozenSegment, IsInFrozenSegment, UpdateFrozenSegment, sorted_table, seg_mapping_table, ro_segment_lookup, etc.) are byte-for-byte identical to before — only the surrounding preprocessor guards were stripped.

💡 Minor: a few double blank lines from mechanical removal

In interface.cpp (around NextObj) and gc.cpp (around ro_segment_lookup), the removal of adjacent #ifdef/#endif blocks leaves consecutive blank lines. This is cosmetic only and consistent with the mechanical nature of the change — not worth a follow-up.

Note

This review was created by GitHub Copilot.

Generated by Code Review for issue #129919 · ● 35.8M · ◷