[mlir][spirv] Add gpu printf op lowering to spirv.CL.printf op (#78510)

This change contains following:
	- adds lowering of printf op to spirv.CL.printf op in GPUToSPIRV pass.
	- Fixes Constant decoration parsing for spirv GlobalVariable.
	- minor modification to spirv.CL.printf op assembly format.

---------

Co-authored-by: Jakub Kuderski <[email protected]>

Author: drprajap

mlir/include/mlir/Dialect/SPIRV/IR/SPIRVCLOps.td

@@ -875,7 +875,7 @@ def SPIRV_CLPrintfOp : SPIRV_CLOp<"printf", 184, []> {
     #### Example:
 
     ```mlir
-    %0 = spirv.CL.printf %0 %1 %2 : (!spirv.ptr<i8, UniformConstant>, (i32, i32)) -> i32
+    %0 = spirv.CL.printf %fmt %1, %2  : !spirv.ptr<i8, UniformConstant>, i32, i32 -> i32
     ```
   }];
 
@@ -889,7 +889,7 @@ def SPIRV_CLPrintfOp : SPIRV_CLOp<"printf", 184, []> {
   );
 
   let assemblyFormat = [{
-  $format `,` $arguments  attr-dict `:`  `(` type($format) `,` `(` type($arguments) `)` `)` `->` type($result)
+   $format ( $arguments^ )? attr-dict `:`  type($format) ( `,` type($arguments)^ )? `->` type($result)
   }];
 
   let hasVerifier = 0;

mlir/lib/Conversion/GPUToSPIRV/GPUToSPIRV.cpp

@@ -121,6 +121,15 @@ class GPUShuffleConversion final : public OpConversionPattern<gpu::ShuffleOp> {
                   ConversionPatternRewriter &rewriter) const override;
 };
 
+class GPUPrintfConversion final : public OpConversionPattern<gpu::PrintfOp> {
+public:
+  using OpConversionPattern::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(gpu::PrintfOp gpuPrintfOp, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override;
+};
+
 } // namespace
 
 //===----------------------------------------------------------------------===//
@@ -597,6 +606,124 @@ class GPUSubgroupReduceConversion final
   }
 };
 
+// Formulate a unique variable/constant name after
+// searching in the module for existing variable/constant names.
+// This is to avoid name collision with existing variables.
+// Example: printfMsg0, printfMsg1, printfMsg2, ...
+static std::string makeVarName(spirv::ModuleOp moduleOp, llvm::Twine prefix) {
+  std::string name;
+  unsigned number = 0;
+
+  do {
+    name.clear();
+    name = (prefix + llvm::Twine(number++)).str();
+  } while (moduleOp.lookupSymbol(name));
+
+  return name;
+}
+
+/// Pattern to convert a gpu.printf op into a SPIR-V CLPrintf op.
+
+LogicalResult GPUPrintfConversion::matchAndRewrite(
+    gpu::PrintfOp gpuPrintfOp, OpAdaptor adaptor,
+    ConversionPatternRewriter &rewriter) const {
+
+  Location loc = gpuPrintfOp.getLoc();
+
+  auto moduleOp = gpuPrintfOp->getParentOfType<spirv::ModuleOp>();
+  if (!moduleOp)
+    return failure();
+
+  // SPIR-V global variable is used to initialize printf
+  // format string value, if there are multiple printf messages,
+  // each global var needs to be created with a unique name.
+  std::string globalVarName = makeVarName(moduleOp, llvm::Twine("printfMsg"));
+  spirv::GlobalVariableOp globalVar;
+
+  IntegerType i8Type = rewriter.getI8Type();
+  IntegerType i32Type = rewriter.getI32Type();
+
+  // Each character of printf format string is
+  // stored as a spec constant. We need to create
+  // unique name for this spec constant like
+  // @printfMsg0_sc0, @printfMsg0_sc1, ... by searching in the module
+  // for existing spec constant names.
+  auto createSpecConstant = [&](unsigned value) {
+    auto attr = rewriter.getI8IntegerAttr(value);
+    std::string specCstName =
+        makeVarName(moduleOp, llvm::Twine(globalVarName) + "_sc");
+
+    return rewriter.create<spirv::SpecConstantOp>(
+        loc, rewriter.getStringAttr(specCstName), attr);
+  };
+  {
+    Operation *parent =
+        SymbolTable::getNearestSymbolTable(gpuPrintfOp->getParentOp());
+
+    ConversionPatternRewriter::InsertionGuard guard(rewriter);
+
+    Block &entryBlock = *parent->getRegion(0).begin();
+    rewriter.setInsertionPointToStart(
+        &entryBlock); // insertion point at module level
+
+    // Create Constituents with SpecConstant by scanning format string
+    // Each character of format string is stored as a spec constant
+    // and then these spec constants are used to create a
+    // SpecConstantCompositeOp.
+    llvm::SmallString<20> formatString(adaptor.getFormat());
+    formatString.push_back('\0'); // Null terminate for C.
+    SmallVector<Attribute, 4> constituents;
+    for (char c : formatString) {
+      spirv::SpecConstantOp cSpecConstantOp = createSpecConstant(c);
+      constituents.push_back(SymbolRefAttr::get(cSpecConstantOp));
+    }
+
+    // Create SpecConstantCompositeOp to initialize the global variable
+    size_t contentSize = constituents.size();
+    auto globalType = spirv::ArrayType::get(i8Type, contentSize);
+    spirv::SpecConstantCompositeOp specCstComposite;
+    // There will be one SpecConstantCompositeOp per printf message/global var,
+    // so no need do lookup for existing ones.
+    std::string specCstCompositeName =
+        (llvm::Twine(globalVarName) + "_scc").str();
+
+    specCstComposite = rewriter.create<spirv::SpecConstantCompositeOp>(
+        loc, TypeAttr::get(globalType),
+        rewriter.getStringAttr(specCstCompositeName),
+        rewriter.getArrayAttr(constituents));
+
+    auto ptrType = spirv::PointerType::get(
+        globalType, spirv::StorageClass::UniformConstant);
+
+    // Define a GlobalVarOp initialized using specialized constants
+    // that is used to specify the printf format string
+    // to be passed to the SPIRV CLPrintfOp.
+    globalVar = rewriter.create<spirv::GlobalVariableOp>(
+        loc, ptrType, globalVarName, FlatSymbolRefAttr::get(specCstComposite));
+
+    globalVar->setAttr("Constant", rewriter.getUnitAttr());
+  }
+  // Get SSA value of Global variable and create pointer to i8 to point to
+  // the format string.
+  Value globalPtr = rewriter.create<spirv::AddressOfOp>(loc, globalVar);
+  Value fmtStr = rewriter.create<spirv::BitcastOp>(
+      loc,
+      spirv::PointerType::get(i8Type, spirv::StorageClass::UniformConstant),
+      globalPtr);
+
+  // Get printf arguments.
+  auto printfArgs = llvm::to_vector_of<Value, 4>(adaptor.getArgs());
+
+  rewriter.create<spirv::CLPrintfOp>(loc, i32Type, fmtStr, printfArgs);
+
+  // Need to erase the gpu.printf op as gpu.printf does not use result vs
+  // spirv::CLPrintfOp has i32 resultType so cannot replace with new SPIR-V
+  // printf op.
+  rewriter.eraseOp(gpuPrintfOp);
+
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // GPU To SPIRV Patterns.
 //===----------------------------------------------------------------------===//
@@ -620,5 +747,6 @@ void mlir::populateGPUToSPIRVPatterns(SPIRVTypeConverter &typeConverter,
       SingleDimLaunchConfigConversion<gpu::SubgroupSizeOp,
                                       spirv::BuiltIn::SubgroupSize>,
       WorkGroupSizeConversion, GPUAllReduceConversion,
-      GPUSubgroupReduceConversion>(typeConverter, patterns.getContext());
+      GPUSubgroupReduceConversion, GPUPrintfConversion>(typeConverter,
+                                                        patterns.getContext());
 }

mlir/lib/Target/SPIRV/Deserialization/Deserializer.cpp

@@ -319,6 +319,7 @@ LogicalResult spirv::Deserializer::processDecoration(ArrayRef<uint32_t> words) {
   case spirv::Decoration::Restrict:
   case spirv::Decoration::RestrictPointer:
   case spirv::Decoration::NoContraction:
+  case spirv::Decoration::Constant:
     if (words.size() != 2) {
       return emitError(unknownLoc, "OpDecoration with ")
              << decorationName << "needs a single target <id>";

mlir/lib/Target/SPIRV/Serialization/Serializer.cpp

@@ -286,6 +286,7 @@ LogicalResult Serializer::processDecorationAttr(Location loc, uint32_t resultID,
   case spirv::Decoration::Restrict:
   case spirv::Decoration::RestrictPointer:
   case spirv::Decoration::NoContraction:
+  case spirv::Decoration::Constant:
     // For unit attributes and decoration attributes, the args list
     // has no values so we do nothing.
     if (isa<UnitAttr, DecorationAttr>(attr))

mlir/test/Conversion/GPUToSPIRV/printf.mlir

@@ -0,0 +1,71 @@
+// RUN: mlir-opt -allow-unregistered-dialect -split-input-file  -convert-gpu-to-spirv -verify-diagnostics %s | FileCheck %s
+
+module attributes {
+  gpu.container_module,
+  spirv.target_env = #spirv.target_env<#spirv.vce<v1.0, [Addresses, Int8, Kernel], []>, #spirv.resource_limits<>>
+} {
+  func.func @main() {
+    %c1 = arith.constant 1 : index
+
+    gpu.launch_func @kernels::@printf
+        blocks in (%c1, %c1, %c1) threads in (%c1, %c1, %c1)
+        args()
+    return
+  }
+  
+  gpu.module @kernels {
+    // CHECK: spirv.module @{{.*}} Physical32 OpenCL
+    // CHECK-DAG: spirv.SpecConstant [[SPECCST:@.*]] = {{.*}} : i8
+    // CHECK-DAG: spirv.SpecConstantComposite [[SPECCSTCOMPOSITE:@.*]] ([[SPECCST]], {{.*}}) : !spirv.array<[[ARRAYSIZE:.*]] x i8>
+    // CHECK-DAG: spirv.GlobalVariable [[PRINTMSG:@.*]] initializer([[SPECCSTCOMPOSITE]]) {Constant}  : !spirv.ptr<!spirv.array<[[ARRAYSIZE]] x i8>, UniformConstant>
+    gpu.func @printf() kernel
+      attributes 
+        {spirv.entry_point_abi = #spirv.entry_point_abi<>} {
+          // CHECK: [[FMTSTR_ADDR:%.*]] = spirv.mlir.addressof [[PRINTMSG]] : !spirv.ptr<!spirv.array<[[ARRAYSIZE]] x i8>, UniformConstant>
+          // CHECK-NEXT: [[FMTSTR_PTR:%.*]] = spirv.Bitcast [[FMTSTR_ADDR]] : !spirv.ptr<!spirv.array<[[ARRAYSIZE]] x i8>, UniformConstant> to !spirv.ptr<i8, UniformConstant>
+          // CHECK-NEXT {{%.*}} = spirv.CL.printf [[FMTSTR_PTR]] : !spirv.ptr<i8, UniformConstant> -> i32
+          gpu.printf "\nHello\n"
+          // CHECK: spirv.Return
+          gpu.return
+    }
+  }
+}
+
+// -----
+
+module attributes {
+  gpu.container_module,
+  spirv.target_env = #spirv.target_env<#spirv.vce<v1.0, [Addresses, Int8, Kernel], []>, #spirv.resource_limits<>>
+} {
+  func.func @main() {
+    %c1   = arith.constant 1 : index
+    %c100 = arith.constant 100: i32
+    %cst_f32 = arith.constant 314.4: f32
+
+    gpu.launch_func @kernels1::@printf_args
+        blocks in (%c1, %c1, %c1) threads in (%c1, %c1, %c1)
+        args(%c100: i32, %cst_f32: f32)
+    return
+  }
+
+   gpu.module @kernels1 {
+    // CHECK: spirv.module @{{.*}} Physical32 OpenCL {
+    // CHECK-DAG: spirv.SpecConstant [[SPECCST:@.*]] = {{.*}} : i8
+    // CHECK-DAG: spirv.SpecConstantComposite [[SPECCSTCOMPOSITE:@.*]] ([[SPECCST]], {{.*}}) : !spirv.array<[[ARRAYSIZE:.*]] x i8>
+    // CHECK-DAG: spirv.GlobalVariable [[PRINTMSG:@.*]] initializer([[SPECCSTCOMPOSITE]]) {Constant}  : !spirv.ptr<!spirv.array<[[ARRAYSIZE]] x i8>, UniformConstant>
+    gpu.func @printf_args(%arg0: i32, %arg1: f32) kernel
+      attributes {spirv.entry_point_abi = #spirv.entry_point_abi<>} {
+        %0 = gpu.block_id x
+        %1 = gpu.block_id y
+        %2 = gpu.thread_id x
+
+        // CHECK: [[FMTSTR_ADDR:%.*]] = spirv.mlir.addressof [[PRINTMSG]] : !spirv.ptr<!spirv.array<[[ARRAYSIZE]] x i8>, UniformConstant>
+        // CHECK-NEXT: [[FMTSTR_PTR1:%.*]] = spirv.Bitcast [[FMTSTR_ADDR]] : !spirv.ptr<!spirv.array<[[ARRAYSIZE]] x i8>, UniformConstant> to !spirv.ptr<i8, UniformConstant>
+        // CHECK-NEXT:  {{%.*}} = spirv.CL.printf [[FMTSTR_PTR1]] {{%.*}}, {{%.*}}, {{%.*}} : !spirv.ptr<i8, UniformConstant>, i32, f32, i32 -> i32
+        gpu.printf "\nHello, world : %d %f \n Thread id: %d\n" %arg0, %arg1, %2: i32, f32, index
+
+        // CHECK: spirv.Return
+        gpu.return
+    }
+  }
+}

mlir/test/Dialect/SPIRV/IR/ocl-ops.mlir

@@ -274,9 +274,9 @@ func.func @rintvec(%arg0 : vector<3xf16>) -> () {
 // spirv.CL.printf
 //===----------------------------------------------------------------------===//
 // CHECK-LABEL: func.func @printf(
-func.func @printf(%arg0 : !spirv.ptr<i8, UniformConstant>, %arg1 : i32, %arg2 : i32) -> i32 {
-  // CHECK: spirv.CL.printf {{%.*}}, {{%.*}}, {{%.*}} : (!spirv.ptr<i8, UniformConstant>, (i32, i32)) -> i32
-  %0 = spirv.CL.printf %arg0, %arg1, %arg2 : (!spirv.ptr<i8, UniformConstant>, (i32, i32)) -> i32
+func.func @printf(%fmt : !spirv.ptr<i8, UniformConstant>, %arg1 : i32, %arg2 : i32) -> i32 {
+  // CHECK: spirv.CL.printf {{%.*}} {{%.*}}, {{%.*}} : !spirv.ptr<i8, UniformConstant>, i32, i32 -> i32
+  %0 = spirv.CL.printf %fmt %arg1, %arg2 : !spirv.ptr<i8, UniformConstant>, i32, i32 -> i32
   return %0 : i32
 }