Remove dead code, unused variable, fix unsigned underflow

- KernelParser.cpp change removes store to `rgn` that was
always overwritten in all codepaths without any load.
- G4_Kernel.hpp change removes potential unsigned underflow
condition `i >= 0` in the for loop always evaluates to true
for unsigned values.
- CISABuilder.cpp change removes `resource` null check
because it must be non-null to reach this codepath.

Author: fda0

IGC/Compiler/CISACodeGen/CISABuilder.cpp

@@ -8247,8 +8247,7 @@ namespace IGC
             // Split d32-V8 -> 2xD32-V4 (or D64-V3/V4 -> D64-V2 & D64-V1/V2).
             // Create operands for 2nd LSC and modify the first's elems
             VISA_PredOpnd* predOpnd2 = GetFlagOperand(m_encoderState.m_flag);
-            VISA_VectorOpnd* globalOffsetOpnd2 =
-                resource ? GetVISALSCSurfaceOpnd(resource->m_surfaceType, resource->m_resource) : nullptr;
+            VISA_VectorOpnd* globalOffsetOpnd2 = GetVISALSCSurfaceOpnd(resource->m_surfaceType, resource->m_resource);
             unsigned blockOffset2 = blockOffset + 128; /* dst offset of 2nd D32-V4(D64-V2/V1) is 4 GRF */
             VISA_RawOpnd* dstOpnd2 = GetRawDestination(dst, blockOffset2);
             VISA_RawOpnd* addressOpnd2 = offset ? GetRawSource(offset) : nullptr;
@@ -8389,8 +8388,7 @@ namespace IGC
             // Split d32-V8 -> 2xD32-V4 (or D64-V3/V4 -> D64-V2 & D64-V1/V2).
             // Create operands for 2nd LSC and modify the first's elems
             VISA_PredOpnd* predOpnd2 = GetFlagOperand(m_encoderState.m_flag);
-            VISA_VectorOpnd* globalOffsetOpnd2 =
-                resource ? GetVISALSCSurfaceOpnd(resource->m_surfaceType, resource->m_resource) : nullptr;
+            VISA_VectorOpnd* globalOffsetOpnd2 = GetVISALSCSurfaceOpnd(resource->m_surfaceType, resource->m_resource);
             unsigned blockOffset2 = blockOffset + 128; /* src1 offset of 2nd D32-V4 (D64-V2/V1) is 4 GRF */
             VISA_RawOpnd* src1Opnd2 = GetRawSource(src, blockOffset2);
             VISA_RawOpnd* addressOpnd2 = GetRawSource(offset);

visa/G4_Kernel.hpp

@@ -192,7 +192,7 @@ class GRFMode {
   }
 
   unsigned getVRTSmallerGRF() const {
-    for (auto i = currentMode - 1; i >= 0 ; --i) {
+    for (auto i = static_cast<int>(currentMode) - 1; i >= 0 ; --i) {
       if (configs[i].VRTEnable)
         return configs[i].numGRF;
     }

visa/iga/IGALibrary/Frontend/KernelParser.cpp

@@ -2203,9 +2203,6 @@ class KernelParser : GenParser {
       // r13.acc2:f
       subregNum = 0;
       mme = ParseMathMacroReg();
-      // region is implicitly <1;1,0>
-      rgn = Region::SRC110;
-      // below we can override it if we really really want to
     } else {
       // regular src with subregister
       // r13.4....