Disable EnableWriteOldFPToStack by default

Disable EnableWriteOldFPToStack by default, since it is no longer needed
for stack walk debug. This change is based on dlei6g proposition. Debug
patch applied.
Before this patch frontend framepointer was saved at the beginning of
the stack call. It is not needed anymore so it is redundant
and affecting performance. Debug info generation change is also needed
to ensure proper DWARF location expression emitting.

Author: Kotynia, Piotr

IGC/Compiler/CISACodeGen/EmitVISAPass.cpp

@@ -10385,14 +10385,6 @@ void EmitPass::emitStackAlloca(GenIntrinsicInst* GII)
 {
     // Static private mem access is done through the FP
     CVariable* pFP = m_currShader->GetFP();
-    if IGC_IS_FLAG_ENABLED(EnableWriteOldFPToStack)
-    {
-        // If we have written the previous FP to the current frame's start, the start of
-        // private memory will be offset by 16 bytes
-        CVariable* tempFP = m_currShader->GetNewVariable(pFP);
-        emitAddPointer(tempFP, pFP, m_currShader->ImmToVariable(getFPOffset(), ISA_TYPE_UD));
-        pFP = tempFP;
-    }
     CVariable* pOffset = m_currShader->GetSymbol(GII->getOperand(0));
     emitAddPointer(m_destination, pFP, pOffset);
 }
@@ -18695,55 +18687,13 @@ void EmitPass::emitPushFrameToStack(unsigned& pushSize)
     m_encoder->Copy(pFP, pSP);
     m_encoder->Push();
 
-    // Allocate 1 extra oword to store previous frame's FP
-    pushSize += IGC_IS_FLAG_ENABLED(EnableWriteOldFPToStack) ? SIZE_OWORD : 0;
-
     // Since we use unaligned oword writes, pushSize should be OW aligned address
     pushSize = int_cast<unsigned>(llvm::alignTo(pushSize, SIZE_OWORD));
 
     if (pushSize != 0)
     {
         // Update SP by pushSize
         emitAddPointer(pSP, pSP, m_currShader->ImmToVariable(pushSize, ISA_TYPE_UD));
-
-        if IGC_IS_FLAG_ENABLED(EnableWriteOldFPToStack)
-        {
-            // Store old FP value to current FP
-            CVariable* pOldFP = m_currShader->GetPrevFP();
-            // If previous FP is null (for kernel frame), we initialize it to 0
-            if (pOldFP == nullptr)
-            {
-                pOldFP = m_currShader->GetNewVariable(pFP);
-                m_encoder->Copy(pOldFP, m_currShader->ImmToVariable(0, pOldFP->GetType()));
-                m_encoder->Push();
-            }
-
-            pFP = ReAlignUniformVariable(pFP, EALIGN_GRF);
-            bool useA64 = (pFP->GetSize() == 8);
-            if (shouldGenerateLSC())
-            {
-                ResourceDescriptor resource;
-                resource.m_surfaceType = ESURFACE_STATELESS;
-                emitLSCStore(nullptr, pOldFP, pFP, 64, 1, 0, &resource, (useA64 ? LSC_ADDR_SIZE_64b : LSC_ADDR_SIZE_32b), LSC_DATA_ORDER_TRANSPOSE, 0, 1);
-                m_encoder->Push();
-            }
-            else
-            {
-                if (useA64)
-                    m_encoder->OWStoreA64(pOldFP, pFP, SIZE_OWORD, 0);
-                else {
-                    // FP is in units of BYTES, but OWStore requires units of OWORDS
-                    CVariable* offsetShr = m_currShader->GetNewVariable(1, ISA_TYPE_UD, EALIGN_DWORD, true, "FPOffset_OW");
-                    m_encoder->SetSimdSize(SIMDMode::SIMD1);
-                    m_encoder->SetNoMask();
-                    m_encoder->SetSrcRegion(0, 0, 1, 0);
-                    m_encoder->Shr(offsetShr, pFP, m_currShader->ImmToVariable(4, ISA_TYPE_UD));
-                    m_encoder->Push();
-                    m_encoder->OWStore(pOldFP, ESURFACE_STATELESS, nullptr, offsetShr, SIZE_OWORD, 0);
-                }
-                m_encoder->Push();
-            }
-        }
     }
 }
 

IGC/Compiler/CISACodeGen/EmitVISAPass.hpp

@@ -257,7 +257,6 @@ class EmitPass : public llvm::FunctionPass
     void emitFlushSamplerCache();
     void emitSurfaceInfo(llvm::GenIntrinsicInst* intrinsic);
 
-    static uint64_t getFPOffset() { return SIZE_OWORD; }
     void emitStackAlloca(llvm::GenIntrinsicInst* intrinsic);
     void emitVLAStackAlloca(llvm::GenIntrinsicInst* intrinsic);
 

IGC/Compiler/DebugInfo/ScalarVISAModule.cpp

@@ -135,9 +135,6 @@ llvm::StringRef ScalarVisaModule::GetVISAFuncName() const
     // matches that used by VISA.
     return getFunction()->getName();
 }
-uint64_t ScalarVisaModule::getFPOffset() const {
-    return EmitPass::getFPOffset();
-}
 
 bool ScalarVisaModule::usesSlot1ScratchSpill() const {
     return m_pShader->ProgramOutput()->getScratchSpaceUsageInSlot1();

IGC/Compiler/DebugInfo/ScalarVISAModule.h

@@ -102,7 +102,6 @@ class ScalarVisaModule final : public IGC::VISAModule {
     bool hasPTO() const  override {
         return getPerThreadOffset() != nullptr;
     }
-    uint64_t getFPOffset() const override;
     int getPTOReg() const override;
     int getFPReg() const override;
 

IGC/Compiler/Optimizer/OpenCLPasses/PrivateMemory/PrivateMemoryResolution.cpp

@@ -251,9 +251,6 @@ bool PrivateMemoryResolution::runOnModule(llvm::Module& M)
                 return 0;
 
             uint32_t currFuncPrivateMem = (uint32_t)(funcIt->second.privateMemoryPerWI);
-            // Add 1 OWORD for FP stack write
-            if IGC_IS_FLAG_ENABLED(EnableWriteOldFPToStack)
-                currFuncPrivateMem += uint32_t(EmitPass::getFPOffset());
 
             CallGraphNode* Node = CG[F];
 
@@ -799,26 +796,6 @@ bool PrivateMemoryResolution::resolveAllocaInstructions(bool privateOnStack)
 
     if (privateOnStack)
     {
-        // If the private memory is on the stack there may be a situation where
-        // some extra data is placed at the beginning of stack frame (e.g. prev FP).
-        // In that case, allocas' alignment may not be satisfied. To prevent this,
-        // a padding is added between that extra data and the private memory.
-        unsigned int allocasExtraOffset = 0;
-        unsigned int padding = 0;
-        if IGC_IS_FLAG_ENABLED(EnableWriteOldFPToStack)
-        {
-            allocasExtraOffset += uint32_t(EmitPass::getFPOffset());
-        }
-
-        if (allocasExtraOffset > 0)
-        {
-            alignment_t privateMemoryAlignment = m_ModAllocaInfo->getPrivateMemAlignment(m_currFunction);
-            padding = iSTD::Align(allocasExtraOffset, size_t(privateMemoryAlignment)) - allocasExtraOffset;
-        }
-
-        modMD->FuncMD[m_currFunction].privateMemoryPerWI += padding;
-        modMD->privateMemoryPerWI += padding;//redundant ?
-
         // Creates intrinsics that will be lowered in the CodeGen and will handle the stack-pointer
         Instruction* simdLaneId16 = entryBuilder.CreateCall(simdLaneIdFunc, llvm::None, VALUE_NAME("simdLaneId16"));
         Value* simdLaneId = entryBuilder.CreateIntCast(simdLaneId16, typeInt32, false, VALUE_NAME("simdLaneId"));
@@ -857,10 +834,6 @@ bool PrivateMemoryResolution::resolveAllocaInstructions(bool privateOnStack)
                 Value* increment = isUniform ? builder.getInt32(0) : simdLaneId;
                 Value* perLaneOffset = builder.CreateMul(increment, ConstantInt::get(typeInt32, bufferSize), VALUE_NAME("perLaneOffset"));
                 Value* totalOffset = builder.CreateAdd(bufferOffset, perLaneOffset, VALUE_NAME(pAI->getName() + ".totalOffset"));
-                if (padding > 0)
-                {
-                    totalOffset = builder.CreateAdd(totalOffset, ConstantInt::get(typeInt32, padding), VALUE_NAME(pAI->getName() + ".totalOffsetWithPadding"));
-                }
                 Function* stackAllocaFunc = GenISAIntrinsic::getDeclaration(m_currFunction->getParent(), GenISAIntrinsic::GenISA_StackAlloca);
                 Value* stackAlloca = builder.CreateCall(stackAllocaFunc, totalOffset, VALUE_NAME("stackAlloca"));
                 privateBuffer = builder.CreatePointerCast(stackAlloca, pAI->getType(), VALUE_NAME(pAI->getName() + ".privateBuffer"));

IGC/DebugInfo/DwarfCompileUnit.cpp

@@ -1276,12 +1276,13 @@ void CompileUnit::addSLMLocation(IGC::DIEBlock *Block, const DbgVariable &DV,
     // There is a private value in the current stack frame.
     // Location encoding is similar to a global variable except SIMD lane
     // location encoding and storage size connected to this, because since it is
-    // uniform we assume this size to be 0. 1 DW_OP_regx <Frame Pointer reg
-    // encoded> 2 DW_OP_const1u <bit-offset to Frame Pointer reg> 3
-    // DW_OP_const1u 64  , i.e. size in bits 4 DW_OP_INTEL_push_bit_piece_stack
-    // 5 DW_OP_plus_uconst  SIZE_OWORD        // i.e. 0x10 taken from
-    // getFPOffset(); same as emitted in EmitPass::emitStackAlloca() 6
-    // DW_OP_plus_uconst storageOffset      // MD: StorageOffset; the offset
+    // uniform we assume this size to be 0.
+    // 1 DW_OP_regx <Frame Pointer reg encoded>
+    // 2 DW_OP_const1u <bit-offset to Frame Pointer reg>
+    // 3 DW_OP_const1u 64, i.e. size in bits
+    // 4 DW_OP_INTEL_push_bit_piece_stack
+    // 6 DW_OP_plus_uconst storageOffset
+    // MD: StorageOffset -> the offset
     // where each variable is stored in the current stack frame
 
     const auto *VISAMod = Loc.GetVISAModule();
@@ -1322,11 +1323,6 @@ void CompileUnit::addSLMLocation(IGC::DIEBlock *Block, const DbgVariable &DV,
                                          // Frame Pointer reg>
     extractSubRegValue(Block, 64);
 
-    addUInt(Block, dwarf::DW_FORM_data1,
-            dwarf::DW_OP_plus_uconst); // 5 DW_OP_plus_uconst  SIZE_OWORD (taken
-                                       // from getFPOffset())
-    addUInt(Block, dwarf::DW_FORM_udata, VISAMod->getFPOffset());
-
     addUInt(Block, dwarf::DW_FORM_data1,
             dwarf::DW_OP_plus_uconst); // 6 DW_OP_plus_uconst storageOffset
     addUInt(Block, dwarf::DW_FORM_udata, storageOffset); // storageOffset
@@ -2829,11 +2825,13 @@ bool CompileUnit::buildFpBasedLoc(const DbgVariable &var, IGC::DIEBlock *Block,
   // 2 DW_OP_const1u <bit-offset to Frame Pointer reg>
   // 3 DW_OP_const1u 64  , i.e. size in bits
   // 4 DW_OP_INTEL_push_bit_piece_stack
-  // 5 DW_OP_plus_uconst  SIZE_OWORD         // i.e. 0x10 taken from
-  // getFPOffset(); same as emitted in EmitPass::emitStackAlloca() 6
-  // DW_OP_push_simd_lane 7 DW_OP_const1u/2u/4u/8u  storageSize   // MD:
-  // StorageSize; the size of the variable 8 DW_OP_mul 9 DW_OP_plus 10
-  // DW_OP_plus_uconst storageOffset      // MD: StorageOffset; the offset where
+  // 5 DW_OP_push_simd_lane
+  // 6 DW_OP_const1u/2u/4u/8u  storageSize
+  // MD: StorageSize -> the size of the variable
+  // 7 DW_OP_mul
+  // 8 DW_OP_plus
+  // 9 DW_OP_plus_uconst storageOffset
+  // MD: StorageOffset -> the offset where
   // each variable is stored in the current stack frame
 
   auto regNumFP = VISAMod->getFPReg();
@@ -2861,11 +2859,6 @@ bool CompileUnit::buildFpBasedLoc(const DbgVariable &var, IGC::DIEBlock *Block,
       bitOffsetToFPReg); // 2 DW_OP_const1u/2u <bit-offset to Frame Pointer reg>
   extractSubRegValue(Block, 64);
 
-  addUInt(Block, dwarf::DW_FORM_data1,
-          dwarf::DW_OP_plus_uconst); // 5 DW_OP_plus_uconst  SIZE_OWORD (taken
-                                     // from getFPOffset())
-  addUInt(Block, dwarf::DW_FORM_udata, VISAMod->getFPOffset());
-
   addUInt(Block, dwarf::DW_FORM_data1,
           DW_OP_INTEL_push_simd_lane);   // 6 DW_OP_INTEL_push_simd_lane
   addConstantUValue(Block, storageSize); // 7 DW_OP_const1u/2u/4u/8u storageSize

IGC/DebugInfo/VISAModule.hpp

@@ -549,7 +549,6 @@ class VISAModule {
   virtual bool hasPTO() const = 0;
   virtual int getPTOReg() const = 0;
   virtual int getFPReg() const = 0;
-  virtual uint64_t getFPOffset() const = 0;
   virtual bool usesSlot1ScratchSpill() const = 0;
 
   virtual llvm::ArrayRef<char> getGenDebug() const = 0;

IGC/VectorCompiler/lib/GenXCodeGen/GenXDebugInfo.cpp

@@ -1055,7 +1055,6 @@ class GenXFunction final : public IGC::VISAModule {
   bool hasPTO() const override { return false; }
   int getPTOReg() const override { return -1; }
   int getFPReg() const override { return -1; }
-  uint64_t getFPOffset() const override { return 16; }
 
   bool usesSlot1ScratchSpill() const override { return false; }
 

IGC/common/igc_flags.h

@@ -394,7 +394,6 @@ DECLARE_IGC_REGKEY(bool, AvoidUsingR0R1,                false, "Do not use r0 an
 DECLARE_IGC_REGKEY(bool, EnableGTLocationDebugging,     true, "Setting this to 1 (true) enables GT location expression emission for GPU debugger", true)
 DECLARE_IGC_REGKEY(bool, UseOffsetInLocation,           true,  "Setting this to 1 (true) preserves private base and per thread offset and removes preservation of any other debug variables", true)
 DECLARE_IGC_REGKEY(bool, EnableRelocations,             false, "Setting this to 1 (true) makes IGC emit relocatable ELF with debug info", true)
-DECLARE_IGC_REGKEY(bool, EnableWriteOldFPToStack,       true,  "Setting this to 1 (true) writes the caller frame's frame-pointer to the start of callee's frame on stack, to support stack walk", false)
 DECLARE_IGC_REGKEY(bool, ZeBinCompatibleDebugging,      true,  "Setting this to 1 (true) enables embed debug info in zeBinary", true)
 DECLARE_IGC_REGKEY(bool, DebugInfoEnforceAmd64EM,       false, "Enforces elf file with the debug infomation to have eMachine set to AMD64", false)
 DECLARE_IGC_REGKEY(bool, DebugInfoValidation,           false, "Enable optional (strict) checks to detect debug information inconsistencies", false)