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Jit: Conditional Escape Analysis and Cloning
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Enhance escape analysis to determine if an object escapes only under
failed GDV tests. If so, clone to create a path of code so that
the object doesn't escape, and then stack allocate the object.

More details in the included document.

Contributes to dotnet#108913
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@AndyAyersMS
AndyAyersMS committed Jan 15, 2025
1 parent cea112c commit 95154f1
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Showing 11 changed files with 2,848 additions and 47 deletions.
800 changes: 800 additions & 0 deletions docs/design/coreclr/jit/DeabstractionAndConditionalEscapeAnalysis.md
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25 changes: 23 additions & 2 deletions src/coreclr/jit/compiler.h
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Expand Up @@ -667,6 +667,9 @@ class LclVarDsc

unsigned char lvRedefinedInEmbeddedStatement : 1; // Local has redefinitions inside embedded statements that
// disqualify it from local copy prop.

unsigned char lvIsEnumerator : 1; // Local is assigned exact class where : IEnumerable<T> via GDV

private:
unsigned char lvIsNeverNegative : 1; // The local is known to be never negative

Expand Down Expand Up @@ -4559,6 +4562,26 @@ class Compiler

unsigned impStkSize; // Size of the full stack

// Enumerator de-abstraction support
//
typedef JitHashTable<GenTree*, JitPtrKeyFuncs<GenTree>, unsigned> NodeToUnsignedMap;

// Map is only set on the root instance.
//
NodeToUnsignedMap* impEnumeratorGdvLocalMap = nullptr;
bool hasImpEnumeratorGdvLocalMap() { return impInlineRoot()->impEnumeratorGdvLocalMap != nullptr; }
NodeToUnsignedMap* getImpEnumeratorGdvLocalMap()
{
Compiler* compiler = impInlineRoot();
if (compiler->impEnumeratorGdvLocalMap == nullptr)
{
CompAllocator alloc(compiler->getAllocator(CMK_Generic));
compiler->impEnumeratorGdvLocalMap = new (alloc) NodeToUnsignedMap(alloc);
}

return compiler->impEnumeratorGdvLocalMap;
}

#define SMALL_STACK_SIZE 16 // number of elements in impSmallStack

struct SavedStack // used to save/restore stack contents.
Expand Down Expand Up @@ -11589,8 +11612,6 @@ class Compiler
return compRoot->m_fieldSeqStore;
}

typedef JitHashTable<GenTree*, JitPtrKeyFuncs<GenTree>, unsigned> NodeToUnsignedMap;

NodeToUnsignedMap* m_memorySsaMap[MemoryKindCount];

// In some cases, we want to assign intermediate SSA #'s to memory states, and know what nodes create those memory
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2 changes: 2 additions & 0 deletions src/coreclr/jit/fgehopt.cpp
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Expand Up @@ -2761,6 +2761,8 @@ BasicBlock* Compiler::fgCloneTryRegion(BasicBlock* tryEntry, CloneTryInfo& info,
// all the EH indicies at or above insertBeforeIndex will shift,
// and the EH table may reallocate.
//
// This addition may also fail, if the table would become too large...
//
EHblkDsc* const clonedOutermostEbd =
fgTryAddEHTableEntries(insertBeforeIndex, regionCount, /* deferAdding */ deferCloning);

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52 changes: 52 additions & 0 deletions src/coreclr/jit/importer.cpp
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Expand Up @@ -3445,6 +3445,21 @@ void Compiler::impImportAndPushBox(CORINFO_RESOLVED_TOKEN* pResolvedToken)
{
GenTreeCall* const call = exprToBox->AsRetExpr()->gtInlineCandidate->AsCall();

// If the call was flagged for possible enumerator cloning, flag the allocation as well.
//
if (compIsForInlining() && hasImpEnumeratorGdvLocalMap())
{
NodeToUnsignedMap* const map = getImpEnumeratorGdvLocalMap();
unsigned enumeratorLcl = BAD_VAR_NUM;
GenTreeCall* const call = impInlineInfo->iciCall;
if (map->Lookup(call, &enumeratorLcl))
{
JITDUMP("Flagging [%06u] for enumerator cloning via V%02u\n", dspTreeID(op1), enumeratorLcl);
map->Remove(call);
map->Set(op1, enumeratorLcl);
}
}

if (call->ShouldHaveRetBufArg())
{
JITDUMP("Must insert newobj stmts for box before call [%06u]\n", dspTreeID(call));
Expand Down Expand Up @@ -6740,6 +6755,26 @@ void Compiler::impImportBlockCode(BasicBlock* block)
{
lvaUpdateClass(lclNum, op1, tiRetVal.GetClassHandleForObjRef());
}

// If we see a local being assigned the result of a GDV-inlineable
// IEnumerable<T>.GetEnumerator, keep track of both the local and the call.
//
if (op1->OperIs(GT_RET_EXPR))
{
JITDUMP(".... checking for GDV of IEnumerable<T>...\n");

GenTreeCall* const call = op1->AsRetExpr()->gtInlineCandidate;
NamedIntrinsic const ni = lookupNamedIntrinsic(call->gtCallMethHnd);

if (ni == NI_System_Collections_Generic_IEnumerable_GetEnumerator)
{
JITDUMP("V%02u value is GDV of IEnumerable<T>.GetEnumerator\n", lclNum);
lvaTable[lclNum].lvIsEnumerator = true;
JITDUMP("Flagging [%06u] for enumerator cloning via V%02u\n", dspTreeID(call), lclNum);
getImpEnumeratorGdvLocalMap()->Set(call, lclNum);
Metrics.EnumeratorGDV++;
}
}
}

/* Filter out simple stores to itself */
Expand Down Expand Up @@ -8838,6 +8873,23 @@ void Compiler::impImportBlockCode(BasicBlock* block)
op1->gtFlags |= GTF_ALLOCOBJ_EMPTY_STATIC;
}

// If the method being imported is an inlinee, and the original call was flagged
// for possible enumerator cloning, flag the allocation as well.
//
if (compIsForInlining() && hasImpEnumeratorGdvLocalMap())
{
NodeToUnsignedMap* const map = getImpEnumeratorGdvLocalMap();
unsigned enumeratorLcl = BAD_VAR_NUM;
GenTreeCall* const call = impInlineInfo->iciCall;
if (map->Lookup(call, &enumeratorLcl))
{
JITDUMP("Flagging [%06u] for enumerator cloning via V%02u\n", dspTreeID(op1),
enumeratorLcl);
map->Remove(call);
map->Set(op1, enumeratorLcl);
}
}

// Remember that this basic block contains 'new' of an object
block->SetFlags(BBF_HAS_NEWOBJ);
optMethodFlags |= OMF_HAS_NEWOBJ;
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7 changes: 7 additions & 0 deletions src/coreclr/jit/importercalls.cpp
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Expand Up @@ -10562,6 +10562,13 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
result = NI_System_Collections_Generic_EqualityComparer_get_Default;
}
}
else if (strcmp(className, "IEnumerable`1") == 0)
{
if (strcmp(methodName, "GetEnumerator") == 0)
{
result = NI_System_Collections_Generic_IEnumerable_GetEnumerator;
}
}
}
else if (strcmp(namespaceName, "Numerics") == 0)
{
Expand Down
16 changes: 16 additions & 0 deletions src/coreclr/jit/indirectcalltransformer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -907,6 +907,22 @@ class IndirectCallTransformer
GenTreeCall* call = compiler->gtCloneCandidateCall(origCall);
call->gtArgs.GetThisArg()->SetEarlyNode(compiler->gtNewLclvNode(thisTemp, TYP_REF));

// If the original call was flagged as one that might inspire enumerator de-abstraction
// cloning, move the flag to the devirtualized call.
//
if (compiler->hasImpEnumeratorGdvLocalMap())
{
Compiler::NodeToUnsignedMap* const map = compiler->getImpEnumeratorGdvLocalMap();
unsigned enumeratorLcl = BAD_VAR_NUM;
if (map->Lookup(origCall, &enumeratorLcl))
{
JITDUMP("Flagging [%06u] for enumerator cloning via V%02u\n", compiler->dspTreeID(call),
enumeratorLcl);
map->Remove(origCall);
map->Set(call, enumeratorLcl);
}
}

INDEBUG(call->SetIsGuarded());

JITDUMP("Direct call [%06u] in block " FMT_BB "\n", compiler->dspTreeID(call), block->bbNum);
Expand Down
1 change: 1 addition & 0 deletions src/coreclr/jit/jitconfigvalues.h
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Expand Up @@ -668,6 +668,7 @@ CONFIG_STRING(JitObjectStackAllocationRange, "JitObjectStackAllocationRange")
RELEASE_CONFIG_INTEGER(JitObjectStackAllocation, "JitObjectStackAllocation", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationRefClass, "JitObjectStackAllocationRefClass", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationBoxedValueClass, "JitObjectStackAllocationBoxedValueClass", 1)
RELEASE_CONFIG_INTEGER(JitObjectStackAllocationConditionalEscape, "JitObjectStackAllocationConditoinalEscape", 1)

RELEASE_CONFIG_INTEGER(JitEECallTimingInfo, "JitEECallTimingInfo", 0)

Expand Down
3 changes: 3 additions & 0 deletions src/coreclr/jit/jitmetadatalist.h
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Expand Up @@ -63,6 +63,7 @@ JITMETADATAMETRIC(ClassGDV, int, 0)
JITMETADATAMETRIC(MethodGDV, int, 0)
JITMETADATAMETRIC(MultiGuessGDV, int, 0)
JITMETADATAMETRIC(ChainedGDV, int, 0)
JITMETADATAMETRIC(EnumeratorGDV, int, 0)
JITMETADATAMETRIC(InlinerBranchFold, int, 0)
JITMETADATAMETRIC(InlineAttempt, int, 0)
JITMETADATAMETRIC(InlineCount, int, 0)
Expand Down Expand Up @@ -90,6 +91,8 @@ JITMETADATAMETRIC(LocalAssertionCount, int, 0)
JITMETADATAMETRIC(LocalAssertionOverflow, int, 0)
JITMETADATAMETRIC(MorphTrackedLocals, int, 0)
JITMETADATAMETRIC(MorphLocals, int, 0)
JITMETADATAMETRIC(EnumeratorGDVProvisionalNoEscape, int, 0)
JITMETADATAMETRIC(EnumeratorGDVCanCloneToEnsureNoEscape, int, 0)

#undef JITMETADATA
#undef JITMETADATAINFO
Expand Down
1 change: 1 addition & 0 deletions src/coreclr/jit/namedintrinsiclist.h
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Original file line number Diff line number Diff line change
Expand Up @@ -248,6 +248,7 @@ enum NamedIntrinsic : unsigned short
//
NI_System_SZArrayHelper_GetEnumerator,
NI_System_Array_T_GetEnumerator,
NI_System_Collections_Generic_IEnumerable_GetEnumerator,
};

#endif // _NAMEDINTRINSICLIST_H_
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