Fix embedded temporary creation

src/jit/lower.cpp

@@ -864,6 +864,67 @@ GenTreePtr Lowering::CreateLocalTempAsg(GenTreePtr rhs,
     return store;
 }
 
+//-----------------------------------------------------------------------------------------------
+// CreateEmbeddedTemporary: Store the result of the given tree in a newly created temporary local
+//                          variable and replace the original use of the tree with the temporary.
+//
+// Arguments:
+//    ppTree - a pointer to the tree use to replace.
+//
+// Return Value:
+//    The newly created store statement.
+//
+// Assumptions:
+//    This may only be called during tree lowering. The callee must ensure that the tree has already
+//    been lowered and is part of compCurStmt and that compCurStmt is in compCurBB.
+//
+// Notes:
+//    The newly created statement is usually an embedded statement but it can also be a top-level
+//    statement if the tree to be replaced extends to the begining of the current statement. If
+//    a top-level statement is created any embedded statements contained in the tree move to the
+//    the new top-level statement, before the current statement. Such embedded statements need to 
+//    be lowered here because the normal lowering code path won't reach them anymore.
+//
+// TODO-Cleanup: 
+//    Some uses of fgInsertEmbeddedFormTemp in lowering could be replaced with this to avoid 
+//    duplication, see LowerArrElem for example.
+
+GenTreeStmt* Lowering::CreateEmbeddedTemporary(GenTree** ppTree)
+{
+    GenTreeStmt* newStmt = comp->fgInsertEmbeddedFormTemp(ppTree);
+
+    // The tree is assumed to be already lowered so the newly created statement 
+    // should not be lowered again.
+    newStmt->gtFlags |= GTF_STMT_SKIP_LOWER;
+
+    assert(newStmt->gtStmtExpr->OperIsLocalStore());
+
+    // If the newly created statement is top-level then we need to manually lower its embedded 
+    // statements, the tree is lowered but some of its embedded statements are yet to be lowered.
+    if (newStmt->gtStmtIsTopLevel())
+    {
+        GenTree* curStmt = comp->compCurStmt;
+
+        for (GenTree* nextEmbeddedStmt = newStmt->gtStmtNextIfEmbedded();
+             nextEmbeddedStmt != nullptr;
+             nextEmbeddedStmt = nextEmbeddedStmt->gtStmt.gtStmtNextIfEmbedded())
+        {
+            // A previous call to CreateEmbeddedTemporary could have created already lowered
+            // embedded statements from the tree.
+            if ((nextEmbeddedStmt->gtFlags & GTF_STMT_SKIP_LOWER) != 0)
+                continue;
+
+            comp->compCurStmt = nextEmbeddedStmt;
+            comp->fgWalkTreePost(&nextEmbeddedStmt->gtStmt.gtStmtExpr, &Lowering::LowerNodeHelper, this, true);
+            nextEmbeddedStmt->gtFlags |= GTF_STMT_SKIP_LOWER;
+        }
+
+        comp->compCurStmt = curStmt;
+    }
+
+    return newStmt;
+}
+
 // This is the main entry point for Lowering.  
 
 // In addition to that, LowerNode is also responsible for initializing the
@@ -3871,8 +3932,7 @@ void Lowering::LowerSignedDivOrMod(GenTreePtr* ppTree, Compiler::fgWalkData* dat
         {
             // We need to use the dividend node multiple times so its value needs to be
             // computed once and stored in a temp variable.
-            GenTreeStmt* newStmt = comp->fgInsertEmbeddedFormTemp(&(divMod->gtOp.gtOp1));
-            newStmt->gtFlags |= GTF_STMT_SKIP_LOWER;
+            CreateEmbeddedTemporary(&(divMod->gtOp.gtOp1));
             dividend = divMod->gtGetOp1();
 
             GenTreeStmt* curStmt = comp->compCurStmt->AsStmt();

src/jit/lower.h

@@ -203,7 +203,7 @@ class Lowering : public Phase
     static bool NodesAreEquivalentLeaves       (GenTreePtr candidate, GenTreePtr storeInd);
 
     GenTreePtr  CreateLocalTempAsg      (GenTreePtr rhs, unsigned refCount, GenTreePtr *ppLclVar = nullptr);
-
+    GenTreeStmt* CreateEmbeddedTemporary(GenTree** ppTree);
     bool AreSourcesPossiblyModified     (GenTree* use, GenTree* src1, GenTree *src2);
     void ReplaceNode                    (GenTree** ppTreeLocation,
                                          GenTree* replacementNode,