Merge scalar phi-nodes into vector one.

If there is a group of scalar phi-node whose input values are values extracted
from a vector, it may be useful to replace this group with a vector phi. This can
simplify the VISA emitter's job of register allocation.

Author: ppogotov

IGC/Compiler/CISACodeGen/ShaderCodeGen.cpp

@@ -75,6 +75,7 @@ SPDX-License-Identifier: MIT
 
 #include "Compiler/CISACodeGen/SLMConstProp.hpp"
 #include "Compiler/Optimizer/OpenCLPasses/SplitStructurePhisPass/SplitStructurePhisPass.hpp"
+#include "Compiler/Optimizer/OpenCLPasses/MergeScalarPhisPass/MergeScalarPhisPass.hpp"
 #include "Compiler/Legalizer/AddRequiredMemoryFences.h"
 #include "Compiler/Optimizer/OpenCLPasses/GenericAddressResolution/GenericAddressDynamicResolution.hpp"
 #include "Compiler/Optimizer/OpenCLPasses/PrivateMemory/PrivateMemoryResolution.hpp"
@@ -229,6 +230,11 @@ void AddAnalysisPasses(CodeGenContext& ctx, IGCPassManager& mpm)
         mpm.add(createSplitLoadsPass());
     }
 
+
+    if (IGC_IS_FLAG_ENABLED(EnableScalarPhisMerger)) {
+        mpm.add(new MergeScalarPhisPass());
+    }
+
     // only limited code-sinking to several shader-type
     // vs input has the URB-reuse issue to be resolved.
     // Also need to understand the performance benefit better.
@@ -1940,6 +1946,7 @@ void OptimizeIR(CodeGenContext* const pContext)
                 mpm.add(createScalarizerPass(SelectiveScalarizer::Auto));
         }
 
+
         mpm.run(*pContext->getModule());
     } // end scope
     COMPILER_TIME_END(pContext, TIME_OptimizationPasses);

IGC/Compiler/InitializePasses.h

@@ -154,6 +154,7 @@ void initializeSimd32ProfitabilityAnalysisPass(llvm::PassRegistry&);
 void initializeSetFastMathFlagsPass(llvm::PassRegistry&);
 void initializeSPIRMetaDataTranslationPass(llvm::PassRegistry&);
 void initializeSplitStructurePhisPassPass(llvm::PassRegistry&);
+void initializeMergeScalarPhisPassPass(llvm::PassRegistry &);
 void initializeSpv2dBlockIOResolutionPass(llvm::PassRegistry&);
 void initializeSpvSubgroupMMAResolutionPass(llvm::PassRegistry&);
 void initializeSplitLoadsPass(llvm::PassRegistry&);

IGC/Compiler/Optimizer/OpenCLPasses/CMakeLists.txt

@@ -56,6 +56,7 @@ add_subdirectory(SpvSubgroupMMAResolution)
 add_subdirectory(StackOverflowDetection)
 add_subdirectory(StatelessToStateful)
 add_subdirectory(SplitStructurePhisPass)
+add_subdirectory(MergeScalarPhisPass)
 add_subdirectory(SubGroupFuncs)
 add_subdirectory(SubGroupReductionPattern)
 add_subdirectory(TransformUnmaskedFunctionsPass)
@@ -109,6 +110,7 @@ set(IGC_BUILD__SRC__Optimizer_OpenCLPasses_All
     ${IGC_BUILD__SRC__OpenCLPasses_ScalarArgAsPointer}
     ${IGC_BUILD__SRC__OpenCLPasses_SetFastMathFlags}
     ${IGC_BUILD__SRC__OpenCLPasses_SplitStructurePhisPass}
+    ${IGC_BUILD__SRC__OpenCLPasses_MergeScalarPhisPass}
     ${IGC_BUILD__SRC__OpenCLPasses_Spv2dBlockIOResolution}
     ${IGC_BUILD__SRC__OpenCLPasses_SpvSubgroupMMAResolution}
     ${IGC_BUILD__SRC__OpenCLPasses_StackOverflowDetection}
@@ -171,6 +173,7 @@ set(IGC_BUILD__HDR__Optimizer_OpenCLPasses_All
     ${IGC_BUILD__HDR__OpenCLPasses_ScalarArgAsPointer}
     ${IGC_BUILD__HDR__OpenCLPasses_SetFastMathFlags}
     ${IGC_BUILD__HDR__OpenCLPasses_SplitStructurePhisPass}
+    ${IGC_BUILD__HDR__OpenCLPasses_MergeScalarPhisPass}
     ${IGC_BUILD__HDR__OpenCLPasses_Spv2dBlockIOResolution}
     ${IGC_BUILD__HDR__OpenCLPasses_SpvSubgroupMMAResolution}
     ${IGC_BUILD__HDR__OpenCLPasses_StackOverflowDetection}
@@ -234,6 +237,7 @@ set(IGC_BUILD_Compiler_OpenCLPasses_Groups
     Compiler__OpenCLPasses_ScalarArgAsPointer
     Compiler__OpenCLPasses_SetFastMathFlags
     Compiler__OpenCLPasses_SplitStructurePhisPass
+    Compiler__OpenCLPasses_MergeScalarPhisPass
     Compiler__OpenCLPasses_StackOverflowDetection
     Compiler__OpenCLPasses_StatelessToStateful
     Compiler__OpenCLPasses_SubGroupFuncs

IGC/Compiler/Optimizer/OpenCLPasses/MergeScalarPhisPass/CMakeLists.txt

@@ -0,0 +1,29 @@
+#=========================== begin_copyright_notice ============================
+#
+# Copyright (C) 2025 Intel Corporation
+#
+# SPDX-License-Identifier: MIT
+#
+#============================ end_copyright_notice =============================
+
+include_directories("${CMAKE_CURRENT_SOURCE_DIR}")
+
+
+set(IGC_BUILD__SRC__MergeScalarPhisPass
+    "${CMAKE_CURRENT_SOURCE_DIR}/MergeScalarPhisPass.cpp"
+  )
+set(IGC_BUILD__SRC__OpenCLPasses_MergeScalarPhisPass ${IGC_BUILD__SRC__MergeScalarPhisPass} PARENT_SCOPE)
+
+set(IGC_BUILD__HDR__MergeScalarPhisPass
+    "${CMAKE_CURRENT_SOURCE_DIR}/MergeScalarPhisPass.hpp"
+  )
+set(IGC_BUILD__HDR__OpenCLPasses_MergeScalarPhisPass ${IGC_BUILD__HDR__MergeScalarPhisPass} PARENT_SCOPE)
+
+
+igc_sg_register(
+    Compiler__OpenCLPasses_MergeScalarPhisPass
+    "MergeScalarPhisPass"
+    FILES
+      ${IGC_BUILD__SRC__MergeScalarPhisPass}
+      ${IGC_BUILD__HDR__MergeScalarPhisPass}
+  )