JIT: Intrinsify Task/ValueTask factory methods#129810
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Intrinsify and recognize the following methods when used directly in runtime async variants: - `Task.FromResult` - `Task.CompletedTask` - `ValueTask.FromResult` - `ValueTask.CompletedTask` - `new ValueTask()` - `ValueTask`-typed `default` - `new ValueTask<T>(T value)`
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Pull request overview
This PR extends the CoreCLR JIT’s “runtime async” optimization pipeline by marking common Task/ValueTask factory helpers as intrinsics and teaching the importer to fold/avoid AsyncHelpers.TransparentAwaitWithResult in more cases, reducing call/alloc overhead in optimized async-return paths.
Changes:
- Mark
Task.CompletedTask,Task.FromResult,ValueTask.CompletedTask,ValueTask.FromResult, andValueTask<TResult>(TResult)with[Intrinsic]to enable JIT recognition. - Add new JIT
NamedIntrinsicIDs plus importer expansion logic for async-callconvFromResult/CompletedTask, and add a newimpFoldAwaitedTopOfStackfast-path for certain ValueTask return patterns. - Improve debug local naming by labeling
ASYNC_CONTINUATION_ILNUMlocals asAsyncCont.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.
Show a summary per file
| File | Description |
|---|---|
| src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/ValueTask.cs | Adds [Intrinsic] to ValueTask.CompletedTask, ValueTask.FromResult, and ValueTask<TResult>(TResult) ctor to enable JIT recognition. |
| src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs | Adds [Intrinsic] to Task.CompletedTask getter and Task.FromResult to enable async-callconv intrinsic expansion. |
| src/coreclr/jit/namedintrinsiclist.h | Introduces new NamedIntrinsic entries for Task/ValueTask factory methods used by the importer. |
| src/coreclr/jit/importercalls.cpp | Implements async-callconv intrinsic expansion/folding for FromResult/CompletedTask, and extends intrinsic lookup for Task/ValueTask methods. |
| src/coreclr/jit/importer.cpp | Refactors return/await wrapping logic and adds impFoldAwaitedTopOfStack to avoid unnecessary TransparentAwaitWithResult calls. |
| src/coreclr/jit/gentree.cpp | Improves local name printing by labeling async continuation locals as AsyncCont. |
| src/coreclr/jit/compiler.h | Adds the impFoldAwaitedTopOfStack declaration. |
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| // Returns: | ||
| // True if the top of stack was folded and pushed on the stack. | ||
| // |
| impPushOnStack(gtNewLclVarNode(returnLcl), typeInfo(TYP_STRUCT)); | ||
| } | ||
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| JITDUMP("Optimized \"return new ValueTask() to return default\n"); |
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| StackEntry se = impPopStack(); | ||
| impPushOnStack(value, se.seTypeInfo); | ||
| JITDUMP("Optimized \"return new ValueTask(value) to return value directly:\n"); |
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| impPopStack(); | ||
| if (info.compRetType == TYP_VOID) | ||
| { | ||
| lastTree->gtBashToNOP(); | ||
| } | ||
| else if (info.compRetType != TYP_STRUCT) | ||
| { | ||
| impPushOnStack(gtNewZeroConNode(info.compRetType), typeInfo(info.compRetType)); | ||
| lastTree->gtBashToNOP(); | ||
| } | ||
| else | ||
| { | ||
| unsigned returnLcl = lvaGrabTemp(true DEBUGARG("Return temp")); | ||
| lvaSetStruct(returnLcl, info.compMethodInfo->args.retTypeClass, false); | ||
| // Reuse the ValueTask zeroing | ||
| lastTree->AsLclVar()->SetLclNum(returnLcl); | ||
| impPushOnStack(gtNewLclVarNode(returnLcl), typeInfo(TYP_STRUCT)); | ||
| } |
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| case NI_System_Threading_Tasks_Task_FromResult: | ||
| case NI_System_Threading_Tasks_ValueTask_FromResult: | ||
| { | ||
| if ((sig->callConv & CORINFO_CALLCONV_ASYNCCALL) == 0) | ||
| { | ||
| break; | ||
| } | ||
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| CORINFO_CLASS_HANDLE typeHnd = sig->sigInst.methInst[0]; | ||
| ClassLayout* layout = nullptr; | ||
| var_types type = TypeHandleToVarType(typeHnd, &layout); |
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| else if (strcmp(className, "ValueTask") == 0) | ||
| { | ||
| if (strcmp(methodName, "FromResult") == 0) | ||
| { | ||
| result = NI_System_Threading_Tasks_ValueTask_FromResult; | ||
| } | ||
| else if (strcmp(methodName, "get_CompletedTask") == 0) | ||
| { | ||
| result = NI_System_Threading_Tasks_ValueTask_get_CompletedTask; | ||
| } | ||
| else if (strcmp(methodName, ".ctor") == 0) | ||
| { | ||
| result = NI_System_Threading_Tasks_ValueTask__ctor; | ||
| } | ||
| } |
This was referenced Jun 25, 2026
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Intrinsify and recognize the following methods when used directly in runtime async context:
Task.FromResultTask.CompletedTaskValueTask.FromResultValueTask.CompletedTasknew ValueTask()ValueTask-typeddefaultnew ValueTask<T>(T value)Example
Before:
After: