Enable a new way to handle InsELt. This is a first

step out of 3 to enable alias in dessa

Change-Id: I7dc2f82ade1fd6a8810f729bfd4981decaa666f4

Author: jgu222

IGC/common/igc_flags.def

@@ -69,7 +69,7 @@ DECLARE_IGC_REGKEY(DWORD, LoopSinkThresholdDelta,       50,  "Do loop sink If th
 DECLARE_IGC_REGKEY(bool, DisableCodeHoisting,           false, "Setting this to 1/true adds a compiler switch to disable code-hoisting")
 DECLARE_IGC_REGKEY(bool, DisableDeSSA,                  false, "Setting this to 1/true adds a compiler switch to disable optimized De-SSA")
 DECLARE_IGC_REGKEY(bool, EnableDeSSAWA,                 true,  "[tmp]Keep some piece of code to avoid perf regression")
-DECLARE_IGC_REGKEY(DWORD, EnableDeSSAAlias,             0, "[tmp]Enable adding alias feature to DeSSA (using PrefCCMap, not InsEltMap")
+DECLARE_IGC_REGKEY(DWORD, EnableDeSSAAlias,             1, "[tmp]Enable adding alias feature to DeSSA (using PrefCCMap, not InsEltMap")
 DECLARE_IGC_REGKEY(bool, EnableDeSSAMemberRootValue,    true, "[tmp]When this is set, root value of dessa is its real member value; otherwise, the root value is just id for a CC.")
 DECLARE_IGC_REGKEY(bool, DisablePayloadCoalescing,      false, "Setting this to 1/true adds a compiler switch to disable payload coalescing optimization for all types")
 DECLARE_IGC_REGKEY(bool, DisablePayloadCoalescing_RT,   false, "Setting this to 1/true adds a compiler switch to disable payload coalescing optimization for RT only")