[SYCL][NFCI] Rework spec constants metadata used for split (#15346)

Addressing review feedback from #15271

Signed-off-by: Sarnie, Nick <nick.sarnie@intel.com>

Author: sarnex

llvm/include/llvm/SYCLLowerIR/SpecConstants.h

@@ -72,11 +72,6 @@ class SpecConstantsPass : public PassInfoMixin<SpecConstantsPass> {
   collectSpecConstantDefaultValuesMetadata(const Module &M,
                                            std::vector<char> &DefaultValues);
 
-  // Name of the metadata which holds a list of all specialization constants
-  // (with associated information) encountered in the module
-  static constexpr char SPEC_CONST_MD_STRING[] =
-      "sycl.specialization-constants";
-
   // Name of the metadata which indicates this module was proccessed with the
   // default values handing mode.
   static constexpr char SPEC_CONST_DEFAULT_VAL_MODULE_MD_STRING[] =

llvm/lib/SYCLLowerIR/ComputeModuleRuntimeInfo.cpp

@@ -150,14 +150,11 @@ PropSetRegTy computeModuleProperties(const Module &M,
     PropSet.add(PropSetRegTy::SYCL_DEVICE_REQUIREMENTS,
                 computeDeviceRequirements(M, EntryPoints).asMap());
   }
-  auto *SpecConstsMD =
-      M.getNamedMetadata(SpecConstantsPass::SPEC_CONST_MD_STRING);
-  bool SpecConstsMet =
-      SpecConstsMD != nullptr && SpecConstsMD->getNumOperands() != 0;
-  if (SpecConstsMet) {
-    // extract spec constant maps per each module
-    SpecIDMapTy TmpSpecIDMap;
-    SpecConstantsPass::collectSpecConstantMetadata(M, TmpSpecIDMap);
+
+  // extract spec constant maps per each module
+  SpecIDMapTy TmpSpecIDMap;
+  SpecConstantsPass::collectSpecConstantMetadata(M, TmpSpecIDMap);
+  if (!TmpSpecIDMap.empty()) {
     PropSet.add(PropSetRegTy::SYCL_SPECIALIZATION_CONSTANTS, TmpSpecIDMap);
 
     // Add property with the default values of spec constants

llvm/lib/SYCLLowerIR/SpecConstants.cpp

@@ -47,6 +47,9 @@ constexpr char SPIRV_GET_SPEC_CONST_VAL[] = "__spirv_SpecConstant";
 constexpr char SPIRV_GET_SPEC_CONST_COMPOSITE[] =
     "__spirv_SpecConstantComposite";
 
+// Name of the metadata which holds a list of all specialization constants (with
+// associated information) encountered in the module
+constexpr char SPEC_CONST_MD_STRING[] = "sycl.specialization-constants";
 // Name of the metadata which holds a default value list of all specialization
 // constants encountered in the module
 constexpr char SPEC_CONST_DEFAULT_VAL_MD_STRING[] =
@@ -1026,9 +1029,6 @@ PreservedAnalyses SpecConstantsPass::run(Module &M,
   for (const auto &P : DefaultsMetadata)
     MDDefaults->addOperand(P);
 
-  if (Mode == HandlingMode::default_values)
-    M.getOrInsertNamedMetadata(SPEC_CONST_DEFAULT_VAL_MODULE_MD_STRING);
-
   return IRModified ? PreservedAnalyses::none() : PreservedAnalyses::all();
 }
 

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

@@ -509,6 +509,10 @@ processSpecConstantsWithDefaultValues(const module_split::ModuleDesc &MD) {
   assert(NewModuleDesc->Props.SpecConstsMet &&
          "This property should be true since the presence of SpecConsts "
          "has been checked before the run of the pass");
+  // Add metadata to the module so we can identify it as the default value split
+  // later.
+  NewModuleDesc->getModule().getOrInsertNamedMetadata(
+      SpecConstantsPass::SPEC_CONST_DEFAULT_VAL_MODULE_MD_STRING);
   NewModuleDesc->rebuildEntryPoints();
   return NewModuleDesc;
 }