[SYCL] Add dummy image generation for virtual functions

llvm/include/llvm/SYCLLowerIR/ModuleSplitter.h

@@ -130,6 +130,7 @@ class ModuleDesc {
   EntryPointGroup EntryPoints;
   bool IsTopLevel = false;
   mutable std::optional<SYCLDeviceRequirements> Reqs;
+  bool IsDummyImage = false;
 
 public:
   struct Properties {
@@ -225,6 +226,9 @@ class ModuleDesc {
 
   void saveSplitInformationAsMetadata();
 
+  ModuleDesc makeDummy() const;
+  bool isDummyImage() { return IsDummyImage; }
+
 #ifndef NDEBUG
   void verifyESIMDProperty() const;
   void dump() const;

llvm/lib/SYCLLowerIR/ModuleSplitter.cpp

@@ -816,6 +816,15 @@ void ModuleDesc::saveSplitInformationAsMetadata() {
         SpecConstantsPass::SPEC_CONST_DEFAULT_VAL_MODULE_MD_STRING);
 }
 
+ModuleDesc ModuleDesc::makeDummy() const {
+  ModuleDesc MD(CloneModule(getModule()));
+  MD.EntryPoints = EntryPoints;
+  MD.IsTopLevel = IsTopLevel;
+  MD.Reqs = Reqs;
+  MD.IsDummyImage = true;
+  return MD;
+}
+
 void EntryPointGroup::saveNames(std::vector<std::string> &Dest) const {
   Dest.reserve(Dest.size() + Functions.size());
   std::transform(Functions.begin(), Functions.end(),

llvm/test/tools/sycl-post-link/virtual-functions/dummy.ll

@@ -0,0 +1,37 @@
+; RUN: sycl-post-link -split=auto -properties -S < %s -o %t.table
+; RUN: FileCheck %s --input-file=%t.table --check-prefix=CHECK-TABLE
+; RUN: FileCheck %s --input-file=%t_0.ll --check-prefix=CHECK-FP64-SPLIT
+; RUN: FileCheck %s --input-file=%t_1.ll --check-prefix=CHECK-FP64-DUMMY
+; RUN: FileCheck %s --input-file=%t_1.prop --check-prefix=CHECK-FP64-DUMMY-PROPS
+; RUN: FileCheck %s --input-file=%t_2.ll --check-prefix=CHECK-FP32-SPLIT
+
+; CHECK-TABLE:      _0.prop
+; CHECK-TABLE-NEXT: _1.prop
+; CHECK-TABLE-NEXT: _2.prop
+
+; CHECK-FP64-SPLIT: define spir_func void @bar()
+; CHECK-FP32-SPLIT: define spir_func void @foo()
+
+; CHECK-FP64-DUMMY: define spir_func void @bar()
+; CHECK-FP64-DUMMY-NEXT: entry:
+; CHECK-FP64-DUMMY-NEXT: ret void
+
+; CHECK-FP64-DUMMY-PROPS: dummy-image=1
+
+define spir_func void @foo() #1 {
+  %x = alloca float
+  ret void
+}
+
+define spir_func void @bar() #1 !sycl_used_aspects !1 {
+  %x = alloca double
+  %d = load double, ptr %x
+  %res = fadd double %d, %d
+  ret void
+}
+
+attributes #1 = { "sycl-module-id"="v.cpp" "indirectly-callable"="setA" }
+
+!sycl_aspects = !{!0}
+!0 = !{!"fp64", i32 6}
+!1 = !{i32 6}

llvm/tools/sycl-post-link/sycl-post-link.cpp

@@ -59,6 +59,7 @@
 #include "llvm/Transforms/Scalar/DCE.h"
 #include "llvm/Transforms/Scalar/EarlyCSE.h"
 #include "llvm/Transforms/Scalar/SROA.h"
+#include "llvm/Transforms/Utils/Cloning.h"
 #include "llvm/Transforms/Utils/GlobalStatus.h"
 
 #include <algorithm>
@@ -296,11 +297,35 @@ void saveModuleIR(Module &M, StringRef OutFilename) {
   MPM.run(M, MAM);
 }
 
-std::string saveModuleIR(Module &M, int I, StringRef Suff) {
-  DUMP_ENTRY_POINTS(M, EmitOnlyKernelsAsEntryPoints, "saving IR");
+std::unique_ptr<Module> makeDummyImageIR(const Module &M) {
+  auto MCopy = CloneModule(M);
+  for (Function &F : MCopy->functions()) {
+    if (!F.hasFnAttribute("indirectly-callable"))
+      continue;
+
+    F.erase(F.begin(), F.end());
+    BasicBlock *newBB = BasicBlock::Create(F.getContext(), "entry", &F);
+    IRBuilder<> builder(newBB);
+    if (F.getReturnType()->isVoidTy())
+      builder.CreateRetVoid();
+    else
+      builder.CreateRet(UndefValue::get(F.getReturnType()));
+  }
+  return MCopy;
+}
+
+std::string saveModuleIR(module_split::ModuleDesc &MD, int I, StringRef Suff) {
+  std::unique_ptr<Module> Storage;
+  Module *M = &MD.getModule();
+  if (MD.isDummyImage()) {
+    Storage = makeDummyImageIR(MD.getModule());
+    M = Storage.get();
+  }
+
+  DUMP_ENTRY_POINTS(*M, EmitOnlyKernelsAsEntryPoints, "saving IR");
   StringRef FileExt = (OutputAssembly) ? ".ll" : ".bc";
   std::string OutFilename = makeResultFileName(FileExt, I, Suff);
-  saveModuleIR(M, OutFilename);
+  saveModuleIR(*M, OutFilename);
   return OutFilename;
 }
 
@@ -318,6 +343,9 @@ std::string saveModuleProperties(module_split::ModuleDesc &MD,
     NewSuff += Target;
   }
 
+  if (MD.isDummyImage())
+    PropSet.add(PropSetRegTy::SYCL_VIRTUAL_FUNCTIONS, "dummy-image", 1);
+
   std::error_code EC;
   std::string SCFile = makeResultFileName(".prop", I, NewSuff);
   raw_fd_ostream SCOut(SCFile, EC);
@@ -425,7 +453,7 @@ void saveModule(std::vector<std::unique_ptr<util::SimpleTable>> &OutTables,
     BaseTriple.Ir = IRFilename.str();
   } else {
     MD.cleanup();
-    BaseTriple.Ir = saveModuleIR(MD.getModule(), I, Suffix);
+    BaseTriple.Ir = saveModuleIR(MD, I, Suffix);
   }
   if (DoSymGen) {
     // save the names of the entry points - the symbol table
@@ -741,6 +769,20 @@ bool isTargetCompatibleWithModule(const std::string &Target,
   return true;
 }
 
+bool hasVirtualFunctionsAndOptionalKernelFeatures(const Module &M) {
+  bool hasVirtualFunctions = false;
+  bool hasOptionalKernelFeatures = false;
+  for (const Function &F : M.functions()) {
+    if (F.hasFnAttribute("indirectly-callable"))
+      hasVirtualFunctions = true;
+    if (F.getMetadata("sycl_used_aspects"))
+      hasOptionalKernelFeatures = true;
+    if (hasVirtualFunctions && hasOptionalKernelFeatures)
+      break;
+  }
+  return hasVirtualFunctions && hasOptionalKernelFeatures;
+}
+
 std::vector<std::unique_ptr<util::SimpleTable>>
 processInputModule(std::unique_ptr<Module> M) {
   // Construct the resulting table which will accumulate all the outputs.
@@ -895,6 +937,21 @@ processInputModule(std::unique_ptr<Module> M) {
 
       ++ID;
     }
+
+    // For kernels with virtual functions and optional kernel features, generate
+    // a dummy image to avoid link errors. A dummy image for a set of virtual
+    // functions is a module with the same set of virtual functions, but with
+    // those function bodies replaced with just a return.
+    bool dummyEmitted = false;
+    for (module_split::ModuleDesc &IrMD : MMs) {
+      if ((dummyEmitted = hasVirtualFunctionsAndOptionalKernelFeatures(
+               IrMD.getModule()))) {
+        auto DummyImage = IrMD.makeDummy();
+        saveModule(Tables, DummyImage, ID, OutIRFileName);
+      }
+    }
+    if (dummyEmitted)
+      ++ID;
   }
   return Tables;
 }