Zero more ARF registers for HW debugging

Some HW debugging tools need ARF to be initialized.  This is to zero
flags in the beginning of each kernels.

This will be controlled by an igc key or visa flag.

Author: jgu222

visa/Optimizer.cpp

@@ -577,6 +577,16 @@ void Optimizer::zeroSomeARF()
         G4_INST* zeroAcc1 = builder.createMov(
             builder.getNativeExecSize(), Acc1Dst, builder.createImm(0, Type_UD), InstOpt_WriteEnable, false);
         (void)mainBB->insertBefore(insertBeforePos, zeroAcc1);
+
+        // Zero flags
+        int num32bitFlags = (int)(builder.getNumFlagRegisters()/2);
+        for (int i = 0; i < num32bitFlags; ++i)
+        {
+            G4_DstRegRegion* flagDst = builder.createDst(builder.phyregpool.getFlagAreg(i), 0, 0, 1, Type_UD);
+            G4_INST* zeroFlag = builder.createMov(
+                g4::SIMD1, flagDst, builder.createImm(0, Type_UD), InstOpt_WriteEnable, false);
+            (void)mainBB->insertBefore(insertBeforePos, zeroFlag);
+        }
     }
 }