Unpin locals, attempt 2 (#70655)

Contributes to #40553

Author: aromaa

src/coreclr/jit/compiler.h

@@ -614,6 +614,8 @@ class LclVarDsc
     unsigned char lvSingleDefDisqualifyReason = 'H';
 #endif
 
+    unsigned char lvAllDefsAreNoGc : 1; // For pinned locals: true if all defs of this local are no-gc
+
 #if FEATURE_MULTIREG_ARGS
     regNumber lvRegNumForSlot(unsigned slotNum)
     {

src/coreclr/jit/gentree.h

@@ -1104,6 +1104,11 @@ struct GenTree
         return true;
     }
 
+    bool IsNotGcDef() const
+    {
+        return IsIntegralConst(0) || IsLocalAddrExpr();
+    }
+
     // LIR flags
     //   These helper methods, along with the flag values they manipulate, are defined in lir.h
     //

src/coreclr/jit/lclvars.cpp

@@ -4234,49 +4234,57 @@ void Compiler::lvaMarkLclRefs(GenTree* tree, BasicBlock* block, Statement* stmt,
 
             /* Is this an assignment to a local variable? */
 
-            if (op1->gtOper == GT_LCL_VAR && op2->gtType != TYP_BOOL)
+            if (op1->gtOper == GT_LCL_VAR)
             {
-                /* Only simple assignments allowed for booleans */
+                LclVarDsc* varDsc = lvaGetDesc(op1->AsLclVarCommon());
 
-                if (tree->gtOper != GT_ASG)
+                if (varDsc->lvPinned && varDsc->lvAllDefsAreNoGc)
                 {
-                    goto NOT_BOOL;
+                    if (!op2->IsNotGcDef())
+                    {
+                        varDsc->lvAllDefsAreNoGc = false;
+                    }
                 }
 
-                /* Is the RHS clearly a boolean value? */
-
-                switch (op2->gtOper)
+                if (op2->gtType != TYP_BOOL)
                 {
-                    unsigned lclNum;
+                    /* Only simple assignments allowed for booleans */
 
-                    case GT_CNS_INT:
+                    if (tree->gtOper != GT_ASG)
+                    {
+                        goto NOT_BOOL;
+                    }
 
-                        if (op2->AsIntCon()->gtIconVal == 0)
-                        {
-                            break;
-                        }
-                        if (op2->AsIntCon()->gtIconVal == 1)
-                        {
-                            break;
-                        }
+                    /* Is the RHS clearly a boolean value? */
 
-                        // Not 0 or 1, fall through ....
-                        FALLTHROUGH;
+                    switch (op2->gtOper)
+                    {
+                        case GT_CNS_INT:
 
-                    default:
+                            if (op2->AsIntCon()->gtIconVal == 0)
+                            {
+                                break;
+                            }
+                            if (op2->AsIntCon()->gtIconVal == 1)
+                            {
+                                break;
+                            }
 
-                        if (op2->OperIsCompare())
-                        {
-                            break;
-                        }
+                            // Not 0 or 1, fall through ....
+                            FALLTHROUGH;
 
-                    NOT_BOOL:
+                        default:
 
-                        lclNum = op1->AsLclVarCommon()->GetLclNum();
-                        noway_assert(lclNum < lvaCount);
+                            if (op2->OperIsCompare())
+                            {
+                                break;
+                            }
 
-                        lvaTable[lclNum].lvIsBoolean = false;
-                        break;
+                        NOT_BOOL:
+
+                            varDsc->lvIsBoolean = false;
+                            break;
+                    }
                 }
             }
         }
@@ -4331,7 +4339,8 @@ void Compiler::lvaMarkLclRefs(GenTree* tree, BasicBlock* block, Statement* stmt,
     {
         if (lvaVarAddrExposed(lclNum))
         {
-            varDsc->lvIsBoolean = false;
+            varDsc->lvIsBoolean      = false;
+            varDsc->lvAllDefsAreNoGc = false;
         }
 
         if (tree->gtOper == GT_LCL_FLD)
@@ -4803,6 +4812,8 @@ void Compiler::lvaComputeRefCounts(bool isRecompute, bool setSlotNumbers)
         {
             varDsc->lvSingleDef             = varDsc->lvIsParam;
             varDsc->lvSingleDefRegCandidate = varDsc->lvIsParam;
+
+            varDsc->lvAllDefsAreNoGc = (varDsc->lvImplicitlyReferenced == false);
         }
     }
 
@@ -4921,6 +4932,13 @@ void Compiler::lvaComputeRefCounts(bool isRecompute, bool setSlotNumbers)
                 varDsc->lvImplicitlyReferenced = 1;
             }
         }
+
+        if (varDsc->lvPinned && varDsc->lvAllDefsAreNoGc)
+        {
+            varDsc->lvPinned = 0;
+
+            JITDUMP("V%02u was unpinned as all def candidates were local.\n", lclNum);
+        }
     }
 }