JIT: don't update early ref counts in morph (#57037)

These updates are a vestige of an earlier time when we could not distinguish
early ref counts from normal ref counts. Updating them makes reasoning using
them during morph tricky, and there's no longer any need to do this.

Prerequisite to fixing #56743.

diff --git a/src/coreclr/jit/morph.cpp b/src/coreclr/jit/morph.cpp
index 6bde695..d23fea5 100644 (file)
--- a/src/coreclr/jit/morph.cpp
+++ b/src/coreclr/jit/morph.cpp
@@ -5069,7 +5069,6 @@ void Compiler::fgMakeOutgoingStructArgCopy(GenTreeCall*         call,
             const bool isNoReturnLastUse = (totalAppearances == 1) && call->IsNoReturn();
             if (isTailCallLastUse || isCallLastUse || isNoReturnLastUse)
             {
-                varDsc->setLvRefCnt(0, RCS_EARLY);
                 args->SetNode(lcl);
                 assert(argEntry->GetNode() == lcl);
 
@@ -17380,6 +17379,7 @@ void Compiler::fgResetImplicitByRefRefCount()
             // optimization for single-use implicit-by-ref params whose single use is as
             // an outgoing call argument.
             varDsc->setLvRefCnt(0, RCS_EARLY);
+            varDsc->setLvRefCntWtd(0, RCS_EARLY);
         }
     }
 
@@ -17530,11 +17530,6 @@ void Compiler::fgRetypeImplicitByRefArgs()
                     {
                         // Set the new parent.
                         fieldVarDsc->lvParentLcl = newLclNum;
-                        // Clear the ref count field; it is used to communicate the number of references
-                        // to the implicit byref parameter when morphing calls that pass the implicit byref
-                        // out as an outgoing argument value, but that doesn't pertain to this field local
-                        // which is now a field of a non-arg local.
-                        fieldVarDsc->setLvRefCnt(0, RCS_EARLY);
                     }
 
                     fieldVarDsc->lvIsParam = false;
@@ -17645,16 +17640,9 @@ void Compiler::fgMarkDemotedImplicitByRefArgs()
                 unsigned structLclNum   = varDsc->lvFieldLclStart;
                 varDsc->lvFieldLclStart = 0;
 
-                // Clear the arg's ref count; this was set during address-taken analysis so that
-                // call morphing could identify single-use implicit byrefs; we're done with
-                // that, and want it to be in its default state of zero when we go to set
-                // real ref counts for all variables.
-                varDsc->setLvRefCnt(0, RCS_EARLY);
-
                 // The temp struct is now unused; set flags appropriately so that we
                 // won't allocate space for it on the stack.
-                LclVarDsc* structVarDsc = &lvaTable[structLclNum];
-                structVarDsc->setLvRefCnt(0, RCS_EARLY);
+                LclVarDsc* structVarDsc     = &lvaTable[structLclNum];
                 structVarDsc->lvAddrExposed = false;
 #ifdef DEBUG
                 structVarDsc->lvUnusedStruct = true;
@@ -17673,7 +17661,6 @@ void Compiler::fgMarkDemotedImplicitByRefArgs()
 
                     // The field local is now unused; set flags appropriately so that
                     // we won't allocate stack space for it.
-                    fieldVarDsc->setLvRefCnt(0, RCS_EARLY);
                     fieldVarDsc->lvAddrExposed = false;
                 }
             }