Turn on UseVMaskPredicate as the default

Enable pixel shader interpolation optimization with vmask predicate
optimization. Limit the change to emitPSInput only

Author: iwwu

IGC/Compiler/CISACodeGen/EmitVISAPass.cpp

@@ -4033,8 +4033,6 @@ void EmitPass::EmitGenericPointersCmp(llvm::Instruction* inst,
 
 void EmitPass::BinaryUnary(llvm::Instruction* inst, const SSource source[2], const DstModifier& modifier)
 {
-    UseVMaskPred();
-
     switch (inst->getOpcode())
     {
     case Instruction::FCmp:
@@ -4447,8 +4445,6 @@ void EmitPass::Unary(e_opcode opCode, const SSource sources[1], const DstModifie
 template<int N>
 void EmitPass::Alu(e_opcode opCode, const SSource sources[N], const DstModifier& modifier)
 {
-    UseVMaskPred();
-
     CVariable* srcs[3] = { nullptr, nullptr, nullptr };
     for (uint i = 0; i < N; i++)
     {

IGC/common/igc_flags.h

@@ -403,7 +403,7 @@ DECLARE_IGC_REGKEY(bool, UseMTInLLD,                    false, "Use multi-thread
 DECLARE_IGC_REGKEY(bool, NoCatchAllDebugLine,           false, "Don't emit special placeholder instruction to map VISA orphan instructions", false)
 DECLARE_IGC_REGKEY(bool, EnableTestSplitI64,            false, "Test legalization that split i64 store unnecessarily, to be deleted once test is done[temp]", true)
 DECLARE_IGC_REGKEY(bool, ShaderDumpTranslationOnly,     false, "Dump LLVM IR right after translation from SPIRV to stderr and ignore all passes", false)
-DECLARE_IGC_REGKEY(bool, UseVMaskPredicate,             false, "Use VMask as predicate for subspan usage", false)
+DECLARE_IGC_REGKEY(bool, UseVMaskPredicate,             true,  "Use VMask as predicate for subspan usage", false)
 DECLARE_IGC_REGKEY(bool, StackOverflowDetection,        false, "Inserts checks for stack overflow when stack calls are used.", true)
 
 DECLARE_IGC_GROUP("IGC Features")