[1.6>1.7] [MERGE #3536 @meg-gupta] Do not peep closure stack symbols

Merge pull request #3536 from meg-gupta:fixclosure

Author: Meghana Gupta

lib/Backend/Lower.cpp

@@ -10078,7 +10078,9 @@ Lowerer::CreateOpndForSlotAccess(IR::Opnd * opnd)
         // Stack closure syms are made to look like slot accesses for the benefit of GlobOpt, so that it can do proper
         // copy prop and implicit call bailout. But what we really want is local stack load/store.
         // Don't do this for loop body, though, since we don't have the value saved on the stack.
-        return IR::SymOpnd::New(dstSym->m_stackSym, 0, TyMachReg, this->m_func);
+        IR::SymOpnd * closureSym = IR::SymOpnd::New(dstSym->m_stackSym, 0, TyMachReg, this->m_func);
+        closureSym->GetStackSym()->m_isClosureSym = true;
+        return closureSym;
     }
 
     int32 offset = dstSym->m_propertyId;

lib/Backend/Peeps.cpp

@@ -384,9 +384,14 @@ Peeps::ClearRegMap()
 void
 Peeps::SetReg(RegNum reg, StackSym *sym)
 {
-    this->ClearReg(sym->scratch.peeps.reg);
     this->ClearReg(reg);
 
+    if (sym->m_isClosureSym)
+    {
+        return;
+    }
+
+    this->ClearReg(sym->scratch.peeps.reg);
     this->regMap[reg] = sym;
     sym->scratch.peeps.reg = reg;
 }

lib/Backend/Sym.cpp

@@ -54,6 +54,7 @@ StackSym::New(SymID id, IRType type, Js::RegSlot byteCodeRegSlot, Func *func)
     stackSym->m_isArgCaptured = false;
     stackSym->m_requiresBailOnNotNumber = false;
     stackSym->m_isCatchObjectSym = false;
+    stackSym->m_isClosureSym = false;
     stackSym->m_builtInIndex = Js::BuiltinFunction::None;
     stackSym->m_slotNum = StackSym::InvalidSlot;
 
@@ -503,7 +504,7 @@ StackSym::CloneDef(Func *func)
         newSym->m_allocated = m_allocated;
         newSym->m_isInlinedArgSlot = m_isInlinedArgSlot;
         newSym->m_isCatchObjectSym = m_isCatchObjectSym;
-
+        newSym->m_isClosureSym = m_isClosureSym;
         newSym->m_type = m_type;
 
         newSym->CopySymAttrs(this);

lib/Backend/Sym.h

@@ -231,6 +231,7 @@ class StackSym: public Sym
     uint8           m_isArgCaptured: 1;       // True if there is a ByteCodeArgOutCapture for this symbol
     uint8           m_nonEscapingArgObjAlias : 1;
     uint8           m_isCatchObjectSym : 1;   // a catch object sym (used while jitting loop bodies)
+    uint            m_isClosureSym : 1;
     IRType          m_type;
     Js::BuiltinFunction m_builtInIndex;