Move Containment Analysis to Lowering

- Ensure that the only changes to child nodes are the specification of srcCandidates
(i.e. the register requirements of the parent/consumer)
- Since this now occurs before redoing dataflow, we don't have complete information on
what lclVars are containable. To mitigate this:
  - In `TreeNodeInfoInit()`, if a lclVar is marked `isRegOptional` but is now untracked,
  change it to be contained.
  - Mark decomposed/promoted fields of long params as `lvDoNotEnregister`
 - Ensure that any new code added after `Lowering` is analyzed as necessary.

- When a value becomes unused, it is no longer contained. (This is needed now because liveness runs after containment analysis)
- Add dumping of nodes deleted as unused.
- Need to set byteable regs, as needed on contained RMW memory ops.

1 files changed, 5 insertions, 2 deletions

diff --git a/src/jit/lir.h b/src/jit/lir.h
index 762c79c3c3..4a71947be7 100644
--- a/src/jit/lir.h
+++ b/src/jit/lir.h
@@ -112,12 +112,12 @@ public:
         GenTree* m_firstNode;
         GenTree* m_lastNode;
 
-        ReadOnlyRange(GenTree* firstNode, GenTree* lastNode);
-
         ReadOnlyRange(const ReadOnlyRange& other) = delete;
         ReadOnlyRange& operator=(const ReadOnlyRange& other) = delete;
 
     public:
+        ReadOnlyRange(GenTree* firstNode, GenTree* lastNode);
+
         class Iterator
         {
             friend class ReadOnlyRange;
@@ -312,6 +312,9 @@ public:
 inline void GenTree::SetUnusedValue()
 {
     gtLIRFlags |= LIR::Flags::UnusedValue;
+#ifndef LEGACY_BACKEND
+    ClearContained();
+#endif
 }
 
 inline void GenTree::ClearUnusedValue()