Fix perf regressions with a recent change.

src/coreclr/jit/compiler.h

@@ -3406,6 +3406,8 @@ class Compiler
     void lvaSetVarLiveInOutOfHandler(unsigned varNum);
     bool lvaVarDoNotEnregister(unsigned varNum);
 
+    void lvSetMinOptsDoNotEnreg();
+
     bool lvaEnregEHVars;
     bool lvaEnregMultiRegVars;
 

src/coreclr/jit/compiler.hpp

@@ -1585,11 +1585,6 @@ inline unsigned Compiler::lvaGrabTemp(bool shortLifetime DEBUGARG(const char* re
     lvaTable[tempNum].lvIsTemp  = shortLifetime;
     lvaTable[tempNum].lvOnFrame = true;
 
-    if (!compEnregLocals())
-    {
-        lvaSetVarDoNotEnregister(tempNum DEBUGARG(Compiler::DNER_NoRegVars));
-    }
-
     // If we've started normal ref counting, bump the ref count of this
     // local, as we no longer do any incremental counting, and we presume
     // this new local will be referenced.

src/coreclr/jit/lclvars.cpp

@@ -1431,11 +1431,6 @@ void Compiler::lvaInitVarDsc(LclVarDsc*              varDsc,
     }
 #endif
 
-    if (!compEnregLocals())
-    {
-        lvaSetVarDoNotEnregister(varNum DEBUGARG(Compiler::DNER_NoRegVars));
-    }
-
 #ifdef DEBUG
     varDsc->SetStackOffset(BAD_STK_OFFS);
 #endif
@@ -1588,6 +1583,23 @@ bool Compiler::lvaVarDoNotEnregister(unsigned varNum)
     return varDsc->lvDoNotEnregister;
 }
 
+//------------------------------------------------------------------------
+// lvInitializeDoNotEnregFlag: a helper to initialize `lvDoNotEnregister` flag
+//    for locals that were created before the compiler decided its optimization level.
+//
+// Assumptions:
+//    compEnregLocals() value is finalized and is set to false.
+//
+void Compiler::lvSetMinOptsDoNotEnreg()
+{
+    JITDUMP("compEnregLocals() is false, setting doNotEnreg flag for all locals.");
+    assert(!compEnregLocals());
+    for (unsigned lclNum = 0; lclNum < lvaCount; lclNum++)
+    {
+        lvaSetVarDoNotEnregister(lclNum DEBUGARG(Compiler::DNER_NoRegVars));
+    }
+}
+
 /*****************************************************************************
  * Returns the handle to the class of the local variable varNum
  */
@@ -2626,7 +2638,6 @@ void Compiler::lvaSetVarDoNotEnregister(unsigned varNum DEBUGARG(DoNotEnregister
             break;
         case DNER_NoRegVars:
             JITDUMP("opts.compFlags & CLFLG_REGVAR is not set\n");
-            assert((opts.compFlags & CLFLG_REGVAR) == 0);
             assert(!compEnregLocals());
             break;
         case DNER_MinOptsGC:
@@ -3503,6 +3514,10 @@ void Compiler::lvaSortByRefCount()
             varDsc->lvTracked = 0;
             lvaSetVarDoNotEnregister(lclNum DEBUGARG(DNER_MinOptsGC));
         }
+        if (!compEnregLocals())
+        {
+            lvaSetVarDoNotEnregister(lclNum DEBUGARG(DNER_NoRegVars));
+        }
 #if defined(JIT32_GCENCODER) && defined(FEATURE_EH_FUNCLETS)
         if (lvaIsOriginalThisArg(lclNum) && (info.compMethodInfo->options & CORINFO_GENERICS_CTXT_FROM_THIS) != 0)
         {

src/coreclr/jit/lower.cpp

@@ -5886,6 +5886,16 @@ PhaseStatus Lowering::DoPhase()
     }
 #endif // !defined(TARGET_64BIT)
 
+    if (!comp->compEnregLocals())
+    {
+        // Lowering is checking if lvDoNotEnregister is already set for contained optimizations.
+        // If we are running without `CLFLG_REGVAR` flag set (`compEnregLocals() == false`)
+        // then we already know that we won't enregister any locals and it is better to set
+        // this flag before we start reading it.
+        // The main reason why this flag is not set is that we are running in minOpts.
+        comp->lvSetMinOptsDoNotEnreg();
+    }
+
     for (BasicBlock* const block : comp->Blocks())
     {
         /* Make the block publicly available */

src/coreclr/jit/morph.cpp

@@ -16004,6 +16004,16 @@ void Compiler::fgMorphBlocks()
 
 #endif
 
+    if (!compEnregLocals())
+    {
+        // Morph is checking if lvDoNotEnregister is already set for some optimizations.
+        // If we are running without `CLFLG_REGVAR` flag set (`compEnregLocals() == false`)
+        // then we already know that we won't enregister any locals and it is better to set
+        // this flag before we start reading it.
+        // The main reason why this flag is not set is that we are running in minOpts.
+        lvSetMinOptsDoNotEnreg();
+    }
+
     /*-------------------------------------------------------------------------
      * Process all basic blocks in the function
      */