[MLIR][NVVM] Reduce the scope of the LLVM_HAS_NVPTX_TARGET guard (#97349)

Most of the code here does not depend on the NVPTX target. In particular
the simple offload can just emit LLVM IR and we can use this without the
NVVM backend being built, which can be useful for a frontend that just
need to serialize the IR and leave it up to the runtime to JIT further.

Author: joker-eph

mlir/lib/Dialect/GPU/Transforms/ModuleToBinary.cpp

@@ -38,25 +38,10 @@ class GpuModuleToBinaryPass
     : public impl::GpuModuleToBinaryPassBase<GpuModuleToBinaryPass> {
 public:
   using Base::Base;
-  void getDependentDialects(DialectRegistry &registry) const override;
   void runOnOperation() final;
 };
 } // namespace
 
-void GpuModuleToBinaryPass::getDependentDialects(
-    DialectRegistry &registry) const {
-  // Register all GPU related translations.
-  registry.insert<gpu::GPUDialect>();
-  registry.insert<LLVM::LLVMDialect>();
-#if LLVM_HAS_NVPTX_TARGET
-  registry.insert<NVVM::NVVMDialect>();
-#endif
-#if MLIR_ENABLE_ROCM_CONVERSIONS
-  registry.insert<ROCDL::ROCDLDialect>();
-#endif
-  registry.insert<spirv::SPIRVDialect>();
-}
-
 void GpuModuleToBinaryPass::runOnOperation() {
   RewritePatternSet patterns(&getContext());
   auto targetFormat =

mlir/lib/Target/LLVM/NVVM/Target.cpp

@@ -157,7 +157,6 @@ SerializeGPUModuleBase::loadBitcodeFiles(llvm::Module &module) {
   return std::move(bcFiles);
 }
 
-#if LLVM_HAS_NVPTX_TARGET
 namespace {
 class NVPTXSerializer : public SerializeGPUModuleBase {
 public:
@@ -532,6 +531,12 @@ NVPTXSerializer::moduleToObject(llvm::Module &llvmModule) {
   if (targetOptions.getCompilationTarget() == gpu::CompilationTarget::Offload)
     return SerializeGPUModuleBase::moduleToObject(llvmModule);
 
+#if !LLVM_HAS_NVPTX_TARGET
+  getOperation()->emitError(
+      "The `NVPTX` target was not built. Please enable it when building LLVM.");
+  return std::nullopt;
+#endif // LLVM_HAS_NVPTX_TARGET
+
   // Emit PTX code.
   std::optional<llvm::TargetMachine *> targetMachine =
       getOrCreateTargetMachine();
@@ -569,7 +574,6 @@ NVPTXSerializer::moduleToObject(llvm::Module &llvmModule) {
   return compileToBinary(*serializedISA);
 #endif // MLIR_ENABLE_NVPTXCOMPILER
 }
-#endif // LLVM_HAS_NVPTX_TARGET
 
 std::optional<SmallVector<char, 0>>
 NVVMTargetAttrImpl::serializeToObject(Attribute attribute, Operation *module,
@@ -581,15 +585,9 @@ NVVMTargetAttrImpl::serializeToObject(Attribute attribute, Operation *module,
     module->emitError("Module must be a GPU module.");
     return std::nullopt;
   }
-#if LLVM_HAS_NVPTX_TARGET
   NVPTXSerializer serializer(*module, cast<NVVMTargetAttr>(attribute), options);
   serializer.init();
   return serializer.run();
-#else
-  module->emitError(
-      "The `NVPTX` target was not built. Please enable it when building LLVM.");
-  return std::nullopt;
-#endif // LLVM_HAS_NVPTX_TARGET
 }
 
 Attribute