Fix a break in subroutine returns.

Change-Id: I42949b528b83e7575f27db8a1731080ae784a79f

Author: weiyu-chen

visa/BuildIR.h

@@ -415,6 +415,7 @@ class IR_Builder {
     FINALIZER_INFO*        metaData;
     CompilerStats       compilerStats;
 
+    int subroutineId = -1;   // the kernel itself has id 0, as we always emit a subroutine label for kernel too
     bool isKernel;
 
     // pre-defined declare that binds to R0 (the entire GRF)

visa/CISA.l

@@ -876,7 +876,7 @@ V0 {
         return NULL_VAR;
     }
 
-[a-zA-Z][a-zA-Z0-9_]* {
+[a-zA-Z_][a-zA-Z0-9_]* {
         TRACE("\n** VAR ");
         CISAlval.string = strdup(yytext);
         return VAR;

visa/TranslationInterface.cpp

@@ -2238,6 +2238,11 @@ int IR_Builder::translateVISACFLabelInst(G4_Label* lab)
 #endif
     createLabelInst(lab, true);
 
+    if (lab->isFuncLabel())
+    {
+        subroutineId++;
+    }
+
 #if defined(MEASURE_COMPILATION_TIME) && defined(TIME_IR_CONSTRUCTION)
     stopTimer(TIMER_VISA_BUILDER_IR_CONSTRUCTION);
 #endif
@@ -2513,7 +2518,7 @@ int IR_Builder::translateVISACFRetInst(VISA_Exec_Size executionSize, VISA_EMask_
     }
     else
     {
-        createCFInst(predOpnd, getIsKernel() ? G4_pseudo_exit : GetGenOpcodeFromVISAOpcode(ISA_RET), exsize,
+        createCFInst(predOpnd, subroutineId == 0 ? G4_pseudo_exit : GetGenOpcodeFromVISAOpcode(ISA_RET), exsize,
             nullptr, nullptr, instOpt);
     }