Add preemptive-only cooperative GC transition holder

[davidwrighton]

Summary

• add GCX_COOP_FROM_PREEMP(), a cooperative-mode holder for sites that are guaranteed to enter in preemptive mode
• restore preemptive mode unconditionally on scope exit, removing the saved incoming-mode state and conditional escape-path logic
• use the holder at 235 proven-preemptive transition sites, including 171 QCall-body sites and 64 additional sites covered by preemptive contracts or explicit transitions
• retain GCX_COOP() at 132 sites where the incoming mode is not guaranteed or unwind behavior requires its defensive restoration

The new holder uses the existing non-nestable assertions in DisablePreemptiveGC() and EnablePreemptiveGC() to detect invalid use in Checked and Debug builds.

Size impact

Measured using build.cmd clr -os browser -c release against a baseline build from the same checkout:

WASM section	Baseline bytes	Changed bytes	Bytes removed	Section removed
FUNCTION	10,089	10,088	1	0.009912%
CODE	3,773,433	3,758,613	14,820	0.392746%
DATA	712,583	712,583	0	0%
Whole corerun.wasm	4,512,822	4,498,001	14,821	0.328420%

As a representative example, the Browser WASM body for the AppDomain_CreateDynamicAssembly QCall decreased from 721 bytes to 611 bytes, a reduction of 110 bytes or 15.257%.

Validation

• build.cmd -subset clr -configuration Checked
• build.cmd clr -os browser -c release

Note

This pull request description was generated with GitHub Copilot.

[azure-pipelines]

Azure Pipelines:
Successfully started running 3 pipeline(s).
13 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[dotnet-policy-service]

Tagging subscribers to this area: @agocke
See info in area-owners.md if you want to be subscribed.

[Copilot]

🔵 Needs a closer look

It changes GC mode transition semantics across a large number of VM/QCall sites, so the regression blast radius is high and needs focused human validation of the “always-enter-preemptive” assumption per call site category.

Pull request overview

This PR introduces a new GC mode transition holder, GCX_COOP_FROM_PREEMP(), intended for call sites that are guaranteed to enter in preemptive mode, and updates a large set of existing GCX_COOP() usages to use the new holder where that precondition is believed to hold.

Changes:

• Add GCX_COOP_FROM_PREEMP() macro + GCCoopFromPreemp holder to provide a smaller preemptive→cooperative scope and an unconditional return to preemptive mode.
• Update many QCall and VM sites that previously used GCX_COOP() to use GCX_COOP_FROM_PREEMP() under the assumption they always enter preemptive.
• Keep GCX_COOP() at sites where the incoming mode is not guaranteed (per PR description).

File summaries

File	Description
src/coreclr/vm/weakreferencenative.cpp	Switch select COM interop QCall regions to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/varargsnative.cpp	Switch ArgIterator QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/util.hpp	Add GCX_COOP_FROM_PREEMP() macro and document usage.
src/coreclr/vm/threads.h	Add GCCoopFromPreemp holder + internal enter/pop helpers for the new transition pattern.
src/coreclr/vm/threads.cpp	Switch arg-buffer swap to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/stubhelpers.cpp	Switch multiple interop QCall bodies to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/stdinterfaces.cpp	Switch COM type info helper scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/runtimehandles.cpp	Switch multiple reflection/runtime-handle QCall scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/reflectioninvocation.cpp	Switch reflection invocation QCall scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/qcall.cpp	Switch QCall handle helpers to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/prestub.cpp	Switch debug/slow-path GC-triggering regions to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/olevariant.cpp	Switch VARIANT conversion QCall scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/nativelibrary.cpp	Switch ALC resolve/managed callback scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/mlinfo.cpp	Switch marshaling metadata/handle scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/methodtable.cpp	Switch interface method-table resolution scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/marshalnative.cpp	Switch many marshal/COM QCall scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/managedmdimport.cpp	Switch managed metadata import array allocation scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/loaderallocator.cpp	Switch loader allocator GC/suspend + tracking setup scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/jitinterface.cpp	Switch various JIT-EE helper scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/jithelpers.cpp	Switch selected helper QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/interoplibinterface_objc.cpp	Switch ObjC reference tracking handle operations to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/interoplibinterface_java.cpp	Switch Java bridge initialization/handle operations to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/interoplibinterface_comwrappers.cpp	Switch ComWrappers handle/cache setup to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/ilstubresolver.cpp	Switch IL stub string literal construction scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/ilmarshalers.cpp	Switch SafeArray marshaling QCall scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/finalizerthread.cpp	Switch browser/WASI finalizer iteration KickOff scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/exceptionhandling.cpp	Switch filter/stackwalk-related QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/dynamicmethod.cpp	Switch multiple LCG resolver scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/dwbucketmanager.hpp	Switch exception-name retrieval scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/dispatchinfo.cpp	Switch managed view synchronization scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/debugdebugger.cpp	Switch debugger-related QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/custommarshalerinfo.cpp	Switch marshaler object setup scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/customattribute.cpp	Switch custom attribute instantiation/data creation scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/crst.cpp	Switch debugger suspend-forbid holder scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/comutilnative.cpp	Switch numerous core QCalls (GC interface, failfast, etc.) to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/comsynchronizable.cpp	Switch thread/lock object QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/commodule.cpp	Switch reflection module RVAs/types QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/comdynamic.cpp	Switch dynamic type creation scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/comdependenthandle.cpp	Switch dependent handle alloc/free QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/comdelegate.cpp	Switch delegate init/reflection helper QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/comconnectionpoints.cpp	Switch connection enumeration scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/class.cpp	Switch EnC static field creation scope to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/ceeload.cpp	Switch module init/profiler callback + stringref resolution scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/assemblynative.cpp	Switch many assembly QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/assembly.cpp	Switch loader-allocator association + profiler callback scopes to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/arraynative.cpp	Switch array allocation/ctor QCalls to GCX_COOP_FROM_PREEMP().
src/coreclr/vm/appdomainnative.cpp	Switch dynamic assembly + intern QCalls to GCX_COOP_FROM_PREEMP().

Review details

• Files reviewed: 47/47 changed files
• Comments generated: 0
• Review effort level: Lite