[MERGE #6098 @wyrichte] Fixes #5990 - fixes incorrect argsInsCount in AsmJs ("this" was being considered in AsmJs)

Merge pull request #6098 from wyrichte:build/wyrichte/asmjs

Author: wyrichte

lib/Backend/BackwardPass.cpp

@@ -7865,7 +7865,8 @@ BackwardPass::DeadStoreInstr(IR::Instr *instr)
 
     if (instr->m_opcode == Js::OpCode::ArgIn_A)
     {
-        //Ignore tracking ArgIn for "this", as argInsCount only tracks other params - unless it is a asmjs function(which doesn't have a "this").
+        // Ignore tracking ArgIn for "this" as argInsCount only tracks other
+        // params, unless it is a AsmJS function (which doesn't have a "this").
         if (instr->GetSrc1()->AsSymOpnd()->m_sym->AsStackSym()->GetParamSlotNum() != 1 || func->GetJITFunctionBody()->IsAsmJsMode())
         {
             Assert(this->func->argInsCount > 0);

lib/Backend/GlobOpt.cpp

@@ -165,7 +165,13 @@ void
 GlobOpt::Optimize()
 {
     this->objectTypeSyms = nullptr;
-    this->func->argInsCount = this->func->GetInParamsCount() - 1;   //Don't include "this" pointer in the count.
+
+    this->func->argInsCount = this->func->GetInParamsCount();
+    if (!func->GetJITFunctionBody()->IsAsmJsMode())
+    {
+        // Don't include "this" pointer in the count when not in AsmJs mode (AsmJS does not have "this").
+        this->func->argInsCount--;
+    }
 
     if (!func->DoGlobOpt())
     {