Jit: Conditional Escape Analysis and Cloning (#111473)

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 #108913

Co-authored-by: Aman Khalid <[email protected]>

Author: AndyAyersMS

docs/design/coreclr/jit/DeabstractionAndConditionalEscapeAnalysis.md

@@ -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
 
@@ -3711,6 +3714,8 @@ class Compiler
         return gtNewStmt(exprClone, stmt->GetDebugInfo());
     }
 
+    Statement* gtLatestStatement(Statement* stmt1, Statement* stmt2);
+
     // Internal helper for cloning a call
     GenTreeCall* gtCloneExprCallHelper(GenTreeCall* call);
 
@@ -4606,6 +4611,26 @@ 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.
@@ -11677,8 +11702,6 @@ 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

src/coreclr/jit/compiler.h

@@ -2860,7 +2860,14 @@ bool BBPredsChecker::CheckEHFinallyRet(BasicBlock* blockPred, BasicBlock* block)
         }
     }
 
-    assert(found && "BBJ_EHFINALLYRET predecessor of block that doesn't follow a BBJ_CALLFINALLY!");
+    if (!found)
+    {
+        JITDUMP(FMT_BB " is successor of finallyret " FMT_BB " but prev block is not a callfinally to " FMT_BB
+                       " (search range was [" FMT_BB "..." FMT_BB "]\n",
+                block->bbNum, blockPred->bbNum, finBeg->bbNum, firstBlock->bbNum, lastBlock->bbNum);
+        assert(!"BBJ_EHFINALLYRET predecessor of block that doesn't follow a BBJ_CALLFINALLY!");
+    }
+
     return found;
 }
 

src/coreclr/jit/fgdiagnostic.cpp

@@ -2552,6 +2552,7 @@ BasicBlock* Compiler::fgCloneTryRegion(BasicBlock* tryEntry, CloneTryInfo& info,
     auto addBlockToClone = [=, &blocks, &visited, &numberOfBlocksToClone](BasicBlock* block, const char* msg) {
         if (!BitVecOps::TryAddElemD(traits, visited, block->bbID))
         {
+            JITDUMP("[already seen]  %s block " FMT_BB "\n", msg, block->bbNum);
             return false;
         }
 
@@ -2781,6 +2782,8 @@ 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);
 
@@ -3000,8 +3003,6 @@ BasicBlock* Compiler::fgCloneTryRegion(BasicBlock* tryEntry, CloneTryInfo& info,
                 cloneTryIndex += indexShift;
             }
 
-            EHblkDsc* const originalEbd = ehGetDsc(originalTryIndex);
-            EHblkDsc* const clonedEbd   = ehGetDsc(cloneTryIndex);
             newBlock->setTryIndex(cloneTryIndex);
             updateBlockReferences(cloneTryIndex);
         }
@@ -3016,8 +3017,6 @@ BasicBlock* Compiler::fgCloneTryRegion(BasicBlock* tryEntry, CloneTryInfo& info,
                 cloneHndIndex += indexShift;
             }
 
-            EHblkDsc* const originalEbd = ehGetDsc(originalHndIndex);
-            EHblkDsc* const clonedEbd   = ehGetDsc(cloneHndIndex);
             newBlock->setHndIndex(cloneHndIndex);
             updateBlockReferences(cloneHndIndex);
 

src/coreclr/jit/fgehopt.cpp

@@ -32679,3 +32679,42 @@ void GenTree::SetMorphed(Compiler* compiler, bool doChildren /* = false */)
     }
 }
 #endif
+
+//------------------------------------------------------------------------
+// gtLatestStmt: determine which of two statements happens later
+//
+// Arguments:
+//    stmt1 - first statement to consider
+//    stmt2 - second statement to consider
+//
+// Returns:
+//    either stmt1 or stmt2, whichever happens later in the block
+//
+Statement* Compiler::gtLatestStatement(Statement* stmt1, Statement* stmt2)
+{
+    if (stmt1 == stmt2)
+    {
+        return stmt1;
+    }
+
+    Statement* cursor1 = stmt1->GetNextStmt();
+    Statement* cursor2 = stmt2->GetNextStmt();
+
+    while (true)
+    {
+        if ((cursor1 == stmt2) || (cursor2 == nullptr))
+        {
+            return stmt2;
+        }
+
+        if ((cursor2 == stmt1) || (cursor1 == nullptr))
+        {
+            return stmt1;
+        }
+
+        cursor1 = cursor1->GetNextStmt();
+        cursor2 = cursor2->GetNextStmt();
+    }
+
+    assert(!"could not determine latest stmt");
+}

src/coreclr/jit/gentree.cpp

@@ -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));
@@ -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 */
@@ -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;

src/coreclr/jit/importer.cpp

@@ -10570,6 +10570,13 @@ 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)
                 {

src/coreclr/jit/importercalls.cpp

@@ -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);

src/coreclr/jit/indirectcalltransformer.cpp

@@ -1392,7 +1392,6 @@ class StrengthReductionContext
     BasicBlock* FindPostUseUpdateInsertionPoint(ArrayStack<CursorInfo>* cursors,
                                                 BasicBlock*             backEdgeDominator,
                                                 Statement**             afterStmt);
-    Statement*  LatestStatement(Statement* stmt1, Statement* stmt2);
     bool        InsertionPointPostDominatesUses(BasicBlock* insertionPoint, ArrayStack<CursorInfo>* cursors);
 
     bool StressProfitability()
@@ -2615,7 +2614,7 @@ BasicBlock* StrengthReductionContext::FindPostUseUpdateInsertionPoint(ArrayStack
             }
             else
             {
-                latestStmt = LatestStatement(latestStmt, cursor.Stmt);
+                latestStmt = m_comp->gtLatestStatement(latestStmt, cursor.Stmt);
             }
         }
 
@@ -2632,44 +2631,6 @@ BasicBlock* StrengthReductionContext::FindPostUseUpdateInsertionPoint(ArrayStack
     return nullptr;
 }
 
-//------------------------------------------------------------------------
-// LatestStatement: Given two statements in the same basic block, return the
-// latter of the two.
-//
-// Parameters:
-//   stmt1 - First statement
-//   stmt2 - Second statement
-//
-// Returns:
-//   Latter of the statements.
-//
-Statement* StrengthReductionContext::LatestStatement(Statement* stmt1, Statement* stmt2)
-{
-    if (stmt1 == stmt2)
-    {
-        return stmt1;
-    }
-
-    Statement* cursor1 = stmt1->GetNextStmt();
-    Statement* cursor2 = stmt2->GetNextStmt();
-
-    while (true)
-    {
-        if ((cursor1 == stmt2) || (cursor2 == nullptr))
-        {
-            return stmt2;
-        }
-
-        if ((cursor2 == stmt1) || (cursor1 == nullptr))
-        {
-            return stmt1;
-        }
-
-        cursor1 = cursor1->GetNextStmt();
-        cursor2 = cursor2->GetNextStmt();
-    }
-}
-
 //------------------------------------------------------------------------
 // InsertionPointPostDominatesUses: Check if a basic block post-dominates all
 // locations specified by the cursors.

src/coreclr/jit/inductionvariableopts.cpp

@@ -670,6 +670,8 @@ 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, "JitObjectStackAllocationConditionalEscape", 1)
+CONFIG_STRING(JitObjectStackAllocationConditionalEscapeRange, "JitObjectStackAllocationConditionalEscapeRange")
 RELEASE_CONFIG_INTEGER(JitObjectStackAllocationArray, "JitObjectStackAllocationArray", 1)
 RELEASE_CONFIG_INTEGER(JitObjectStackAllocationSize, "JitObjectStackAllocationSize", 528)
 

src/coreclr/jit/jitconfigvalues.h

@@ -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)
@@ -92,6 +93,8 @@ 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

src/coreclr/jit/jitmetadatalist.h

@@ -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_