Run fgMorphCopyBlock for newly inserted assignment

When one return modification is turned on, the current implementation of
fgMorphBlocks converts the return statement as an assigment at the end of
block aftter fgMorphStmts is performed.

As a result, unfortunately, the newly inserted assignment statement is
never morphed, which results in some strange behavior inside codegen
(which is discussed in dotnet/coreclr#5357).

This commit tries to run fgMorphCopyBlock on newly inserted assignment in
order to fix dotnet/coreclr#5357.

Commit migrated from https://github.com/dotnet/coreclr/commit/6b81f2252f1815b6c5cf6776206d623e625e1712

diff --git a/src/coreclr/src/jit/morph.cpp b/src/coreclr/src/jit/morph.cpp
index e09e96b..495f0e2 100644 (file)
--- a/src/coreclr/src/jit/morph.cpp
+++ b/src/coreclr/src/jit/morph.cpp
@@ -14856,7 +14856,9 @@ void                Compiler::fgMorphBlocks()
                     noway_assert(ret->gtGetOp1() != nullptr);
                     noway_assert(ret->gtGetOp2() == nullptr);
 
-                    last->gtStmt.gtStmtExpr = gtNewTempAssign(genReturnLocal, ret->gtGetOp1());
+                    GenTreePtr tree = gtNewTempAssign(genReturnLocal, ret->gtGetOp1());
+
+                    last->gtStmt.gtStmtExpr = (tree->OperIsCopyBlkOp()) ? fgMorphCopyBlock(tree) : tree;
 
                     //make sure that copy-prop ignores this assignment.
                     last->gtStmt.gtStmtExpr->gtFlags |= GTF_DONT_CSE;