Recognize more "local addr" trees as invariant (#68484)

This will ensure we do not evaluate e.g. the retbuffer into a temp when
unnecessary.

src/coreclr/jit/compiler.h

@@ -4108,6 +4108,7 @@ class Compiler
     static LONG jitNestingLevel;
 #endif // DEBUG
 
+    static bool impIsInvariant(const GenTree* tree);
     static bool impIsAddressInLocal(const GenTree* tree, GenTree** lclVarTreeOut = nullptr);
 
     void impMakeDiscretionaryInlineObservations(InlineInfo* pInlineInfo, InlineResult* inlineResult);

src/coreclr/jit/gentree.cpp

@@ -16308,7 +16308,7 @@ bool GenTree::IsLocalExpr(Compiler* comp, GenTreeLclVarCommon** pLclVarTree, Fie
 // If this tree evaluates some sum of a local address and some constants,
 // return the node for the local being addressed
 
-GenTreeLclVarCommon* GenTree::IsLocalAddrExpr()
+const GenTreeLclVarCommon* GenTree::IsLocalAddrExpr() const
 {
     if (OperGet() == GT_ADDR)
     {
@@ -22865,7 +22865,7 @@ bool GenTreeLclFld::IsOffsetMisaligned() const
 
 bool GenTree::IsInvariant() const
 {
-    return OperIsConst() || Compiler::impIsAddressInLocal(this);
+    return OperIsConst() || IsLocalAddrExpr();
 }
 
 //------------------------------------------------------------------------

src/coreclr/jit/gentree.h

@@ -1916,7 +1916,11 @@ struct GenTree
 
     // Simpler variant of the above which just returns the local node if this is an expression that
     // yields an address into a local
-    GenTreeLclVarCommon* IsLocalAddrExpr();
+    const GenTreeLclVarCommon* IsLocalAddrExpr() const;
+    GenTreeLclVarCommon*       IsLocalAddrExpr()
+    {
+        return const_cast<GenTreeLclVarCommon*>(static_cast<const GenTree*>(this)->IsLocalAddrExpr());
+    }
 
     // Determine if this tree represents the value of an entire implicit byref parameter,
     // and if so return the tree for the parameter.

src/coreclr/jit/importer.cpp

@@ -18902,14 +18902,39 @@ bool Compiler::impIsValueType(typeInfo* pTypeInfo)
     }
 }
 
-/*****************************************************************************
- *  Check to see if the tree is the address of a local or
-    the address of a field in a local.
-
-    *lclVarTreeOut will contain the GT_LCL_VAR tree when it returns true.
-
- */
+//------------------------------------------------------------------------
+// impIsInvariant: check if a tree (created during import) is invariant.
+//
+// Arguments:
+//   tree -- The tree
+//
+// Returns:
+//   true if it is invariant
+//
+// Remarks:
+//   This is a variant of GenTree::IsInvariant that is more suitable for use
+//   during import. Unlike that function, this one handles GT_FIELD nodes.
+//
+bool Compiler::impIsInvariant(const GenTree* tree)
+{
+    return tree->OperIsConst() || impIsAddressInLocal(tree);
+}
 
+//------------------------------------------------------------------------
+// impIsAddressInLocal:
+//   Check to see if the tree is the address of a local or
+//   the address of a field in a local.
+// Arguments:
+//     tree -- The tree
+//     lclVarTreeOut -- [out] the local that this points into
+//
+// Returns:
+//     true if it points into a local
+//
+// Remarks:
+//   This is a variant of GenTree::IsLocalAddrExpr that is more suitable for
+//   use during import. Unlike that function, this one handles GT_FIELD nodes.
+//
 bool Compiler::impIsAddressInLocal(const GenTree* tree, GenTree** lclVarTreeOut)
 {
     if (tree->gtOper != GT_ADDR)
@@ -19520,7 +19545,7 @@ void Compiler::impInlineRecordArgInfo(InlineInfo*   pInlineInfo,
         INDEBUG(curArgVal->AsLclVar()->gtLclILoffs = argNum;)
     }
 
-    if (curArgVal->IsInvariant())
+    if (impIsInvariant(curArgVal))
     {
         inlCurArgInfo->argIsInvariant = true;
         if (inlCurArgInfo->argIsThis && (curArgVal->gtOper == GT_CNS_INT) && (curArgVal->AsIntCon()->gtIconVal == 0))