[Autobackout][FuncReg]Revert of change: 81b88fa

Fix an incorrect condition when deciding if an unreferenced dcl can be
removed from list.

Author: pratikashar

IGC/Compiler/CISACodeGen/CISABuilder.cpp

@@ -3869,7 +3869,7 @@ namespace IGC
         }
 
         if ((context->type == ShaderType::OPENCL_SHADER || context->type == ShaderType::COMPUTE_SHADER) &&
-            m_program->m_Platform->preemptionSupported() && IGC_IS_FLAG_ENABLED(EnablePreemption))
+            VISAPlatform >= GENX_SKL && IGC_IS_FLAG_ENABLED(EnablePreemption))
         {
             SaveOption(vISA_enablePreemption, true);
         }

IGC/Compiler/CISACodeGen/Platform.hpp

@@ -711,13 +711,6 @@ bool supportHeaderRTW() const
 {
     return true;
 }
-
-bool preemptionSupported() const
-{
-
-    return GetPlatformFamily() >= IGFX_GEN9_CORE;
-};
-
 };
 
 }//namespace IGC

visa/BuildIRImpl.cpp

@@ -675,20 +675,23 @@ void IR_Builder::createPreDefinedVars()
 
 void IR_Builder::createBuiltinDecls()
 {
-    // realR0 is always tied to physical r0
+
     auto numR0DW = numEltPerGRF<Type_UD>();
-    realR0 = createDeclareNoLookup(
-        "BuiltInR0",
+    builtinR0 = createDeclareNoLookup(
+        "BuiltinR0",
         G4_INPUT,
         numR0DW,
         1,
         Type_UD);
-    realR0->getRegVar()->setPhyReg(phyregpool.getGreg(0), 0);
+    builtinR0->getRegVar()->setPhyReg(phyregpool.getGreg(0), 0);
+    realR0 = builtinR0;
 
-    // builtinR0 either gets allocated to r0 or to a different
-    // register depending on conditions in RA.
-    builtinR0 = createTempVar(numR0DW, Type_UD, GRFALIGN, "R0_Copy");
-    builtinR0->setDoNotSpill();
+    if (m_options->getOption(vISA_enablePreemption))
+    {
+        G4_Declare *R0CopyDcl = createTempVar(numR0DW, Type_UD, GRFALIGN);
+        builtinR0 = R0CopyDcl;
+        R0CopyDcl->setDoNotSpill();
+    }
 
     builtinA0 = createDeclareNoLookup(
         "BuiltinA0",

visa/GraphColor.cpp

@@ -9545,8 +9545,11 @@ int GlobalRA::coloringRegAlloc()
 
         // bind builtinR0 to the reserved stack call ABI GRF so that caller and
         // callee can agree on which GRF to use for r0
-        builder.getBuiltinR0()->getRegVar()->setPhyReg(
-            builder.phyregpool.getGreg(kernel.getThreadHeaderGRF()), 0);
+        if (builder.getOption(vISA_enablePreemption))
+        {
+            builder.getBuiltinR0()->getRegVar()->setPhyReg(
+                builder.phyregpool.getGreg(kernel.getThreadHeaderGRF()), 0);
+        }
     }
 
     if (!isReRAPass())

visa/LinearScanRA.cpp

@@ -785,6 +785,7 @@ void LinearScanRA::preRAAnalysis()
         const Options* opt = builder.getOptions();
         if (kernel.getInt32KernelAttr(Attributes::ATTR_Target) != VISA_3D ||
             opt->getOption(vISA_enablePreemption) ||
+            (kernel.fg.getHasStackCalls() || kernel.fg.getIsStackCallFunc()) ||
             opt->getOption(vISA_ReserveR0))
         {
             pregs->setR0Forbidden();

visa/LocalRA.cpp

@@ -298,6 +298,7 @@ void LocalRA::preLocalRAAnalysis()
         const Options *opt = builder.getOptions();
         if (kernel.getInt32KernelAttr(Attributes::ATTR_Target) != VISA_3D ||
             opt->getOption(vISA_enablePreemption) ||
+            stackCallRegSize > 0 ||
             opt->getOption(vISA_ReserveR0))
         {
             pregs->setR0Forbidden();
@@ -997,7 +998,8 @@ void GlobalRA::removeUnreferencedDcls()
         return (dcl->getRegFile() == G4_GRF || dcl->getRegFile() == G4_INPUT) &&
             getNumRefs(dcl) == 0 &&
             dcl->getRegVar()->isPhyRegAssigned() == false &&
-            dcl != kernel.fg.builder->getBuiltinR0()
+            !(kernel.fg.builder->getOption(vISA_enablePreemption) &&
+                dcl == kernel.fg.builder->getBuiltinR0())
             ;
     };
 

visa/Optimizer.cpp

@@ -168,17 +168,6 @@ void Optimizer::regAlloc()
 
     fg.prepareTraversal();
 
-    // realR0 and BuiltInR0 are 2 different dcls.
-    // realR0 is always tied to physical r0.
-    // if copy of r0 isnt needed then set latter to r0 as well.
-    // if copy of r0 is required, then let RA decide allocation of BuiltInR0.
-    if (!R0CopyNeeded())
-    {
-        // when no copy is needed, make BuiltInR0 an alias of realR0
-        builder.getBuiltinR0()->setAliasDeclare(builder.getRealR0(), 0);
-        builder.getBuiltinR0()->getRegVar()->setPhyReg(builder.getRealR0()->getRegVar()->getPhyReg(), 0);
-    }
-
     //
     // assign registers
     //
@@ -1033,7 +1022,7 @@ void Optimizer::initOptimizations()
     INITIALIZE_PASS(dumpPayload,             vISA_dumpPayload,             TimerID::MISC_OPTS);
     INITIALIZE_PASS(normalizeRegion,         vISA_EnableAlways,            TimerID::MISC_OPTS);
     INITIALIZE_PASS(collectStats,            vISA_EnableAlways,            TimerID::MISC_OPTS);
-    INITIALIZE_PASS(createR0Copy,            vISA_EnableAlways,            TimerID::MISC_OPTS);
+    INITIALIZE_PASS(createR0Copy,            vISA_enablePreemption,        TimerID::MISC_OPTS);
     INITIALIZE_PASS(initializePayload,       vISA_InitPayload,             TimerID::NUM_TIMERS);
     INITIALIZE_PASS(cleanupBindless,         vISA_enableCleanupBindless,   TimerID::OPTIMIZER);
     INITIALIZE_PASS(countGRFUsage,           vISA_PrintRegUsage,           TimerID::MISC_OPTS);
@@ -1427,23 +1416,6 @@ void Optimizer::accSubPostSchedule()
     accSub.run();
 }
 
-bool Optimizer::R0CopyNeeded()
-{
-    if (kernel.getOption(vISA_enablePreemption))
-    {
-        return true;
-    }
-
-    if (builder.getIsKernel() && kernel.fg.getHasStackCalls())
-    {
-        // As per VISA ABI, last register in GRF file should
-        // contain copy of r0.
-        return true;
-    }
-
-    return false;
-}
-
 int Optimizer::optimization()
 {
     // remove redundant message headers.
@@ -7456,12 +7428,6 @@ bool Optimizer::foldPseudoAndOr(G4_BB* bb, INST_LIST_ITER& ii)
             return;
         }
 
-        // r0 copy is needed only if:
-        // a. pre-emption VISA option is enabled OR
-        // b. current object is kernel with stack calls since VISA ABI requires r0 copy to be available in a pre-defined register
-        if (!R0CopyNeeded())
-            return;
-
         // Skip copying of ``copy of R0'' if it's never assigned, a case where
         // ``copy of R0'' is never used. As EOT always use ``copy of R0'', that
         // case only happens for synthetic tests where no practical code is

visa/Optimizer.h

@@ -196,9 +196,6 @@ class Optimizer
 
     void accSubPostSchedule();
 
-    // return true if BuiltInR0 gets a different allocation than r0
-    bool R0CopyNeeded();
-
 private:
     /* below member functions are used for message header opt */
     bool isHeaderOptCandidate(G4_INST *, G4_INST *);

visa/PhyRegUsage.cpp

@@ -1287,6 +1287,7 @@ void getForbiddenGRFs(
     if (kernel.getKernelType() != VISA_3D ||
         kernel.getOption(vISA_enablePreemption) ||
         reserveSpillSize > 0 ||
+        stackCallRegSize > 0 ||
         kernel.getOption(vISA_ReserveR0))
     {
         regNum.push_back(0);