JIT: Add a pass of liveness for the new locals inside physical promot…

…ion (#86043)

Used when decomposing stores to skip the fields that are dying and the remainder if it is dying. Also allows forward sub to kick in for the inserted replacement locals.

src/coreclr/jit/CMakeLists.txt

@@ -160,6 +160,7 @@ set( JIT_SOURCES
   phase.cpp
   promotion.cpp
   promotiondecomposition.cpp
+  promotionliveness.cpp
   rangecheck.cpp
   rationalize.cpp
   redundantbranchopts.cpp

src/coreclr/jit/compiler.h

@@ -513,6 +513,10 @@ class LclVarDsc
     {
         return lvTracked && lvType != TYP_STRUCT;
     }
+#ifdef DEBUG
+    unsigned char lvTrackedWithoutIndex : 1; // Tracked but has no lvVarIndex (i.e. only valid GTF_VAR_DEATH flags, used
+                                             // by physical promotion)
+#endif
     unsigned char lvPinned : 1; // is this a pinned variable?
 
     unsigned char lvMustInit : 1; // must be initialized

src/coreclr/jit/gentree.cpp

@@ -11936,7 +11936,6 @@ void Compiler::gtDispLocal(GenTreeLclVarCommon* tree, IndentStack* indentStack)
                     printf(" ");
                     fieldVarDsc->PrintVarReg();
                 }
-
                 if (fieldVarDsc->lvTracked && fgLocalVarLivenessDone && tree->IsLastUse(index))
                 {
                     printf(" (last use)");
@@ -11946,7 +11945,8 @@ void Compiler::gtDispLocal(GenTreeLclVarCommon* tree, IndentStack* indentStack)
     }
     else // a normal not-promoted lclvar
     {
-        if (varDsc->lvTracked && fgLocalVarLivenessDone && ((tree->gtFlags & GTF_VAR_DEATH) != 0))
+        if ((varDsc->lvTracked || varDsc->lvTrackedWithoutIndex) && fgLocalVarLivenessDone &&
+            ((tree->gtFlags & GTF_VAR_DEATH) != 0))
         {
             printf(" (last use)");
         }

src/coreclr/jit/lclvars.cpp

@@ -3564,6 +3564,7 @@ void Compiler::lvaSortByRefCount()
 
         // Start by assuming that the variable will be tracked.
         varDsc->lvTracked = 1;
+        INDEBUG(varDsc->lvTrackedWithoutIndex = 0);
 
         if (varDsc->lvRefCnt(lvaRefCountState) == 0)
         {