disable default rocm path

Author: fabianmcg

mlir/lib/Dialect/GPU/CMakeLists.txt

@@ -106,7 +106,7 @@ if(MLIR_ENABLE_ROCM_CONVERSIONS)
       "Building mlir with ROCm support requires the AMDGPU backend")
   endif()
 
-  set(DEFAULT_ROCM_PATH "/opt/rocm" CACHE PATH "Fallback path to search for ROCm installs")
+  set(DEFAULT_ROCM_PATH "" CACHE PATH "Fallback path to search for ROCm installs")
   target_compile_definitions(obj.MLIRGPUTransforms
     PRIVATE
     __DEFAULT_ROCM_PATH__="${DEFAULT_ROCM_PATH}"

mlir/lib/Target/LLVM/CMakeLists.txt

@@ -123,11 +123,6 @@ add_mlir_dialect_library(MLIRROCDLTarget
   )
 
 if(MLIR_ENABLE_ROCM_CONVERSIONS)
-  if (NOT ("AMDGPU" IN_LIST LLVM_TARGETS_TO_BUILD))
-    message(SEND_ERROR
-      "Building mlir with ROCm support requires the AMDGPU backend")
-  endif()
-
   if (DEFINED ROCM_PATH)
     set(DEFAULT_ROCM_PATH "${ROCM_PATH}" CACHE PATH "Fallback path to search for ROCm installs")
   elseif(DEFINED ENV{ROCM_PATH})