Add support for .cu->.cpp copy

Signed-off-by: Luka Govedič <[email protected]>

Author: ProExpertProg

CMakeLists.txt

@@ -284,21 +284,39 @@ elseif (VLLM_GPU_LANG STREQUAL "HIP")
         list(APPEND FA3_GEN_SRCS_CU ${FILE_HIP})
     endforeach ()
 
-    # TODO: copy cpp->cu for correct hipification
-    #  - try copying into gen/ or maybe even directly into build-tree (make sure that it's where hipify would copy it)
+    # These files are "converted" to .cu before being passed to torch.build_extension on upstream.
+    # We need to do the same so that hipify treats them correctly. We copy the files in the source tree like upstream.
+    set(VLLM_FA2_CPP_CU_SRCS
+        # csrc/flash_attn_ck/flash_api.cpp # only contains declarations & PyBind
+        csrc/flash_attn_ck/flash_common.cpp
+        csrc/flash_attn_ck/mha_bwd.cpp
+        csrc/flash_attn_ck/mha_fwd_kvcache.cpp
+        csrc/flash_attn_ck/mha_fwd.cpp
+        csrc/flash_attn_ck/mha_varlen_bwd.cpp
+        csrc/flash_attn_ck/mha_varlen_fwd.cpp
+    )
+
+    foreach(CPP_FILE ${VLLM_FA2_CPP_CU_SRCS})
+        string(REGEX REPLACE "\.cpp$" ".cu" CU_FILE ${CPP_FILE})
+        set(CU_FILE_ABS ${CMAKE_CURRENT_SOURCE_DIR}/${CU_FILE})
+        set(CPP_FILE_ABS ${CMAKE_CURRENT_SOURCE_DIR}/${CPP_FILE})
+        add_custom_command(
+                OUTPUT ${CU_FILE_ABS}
+                COMMAND ${CMAKE_COMMAND} -E copy ${CPP_FILE_ABS} ${CU_FILE_ABS}
+                DEPENDS ${CPP_FILE_ABS}
+                COMMENT "Copying ${CPP_FILE} to ${CU_FILE_ABS}"
+        )
+        list(APPEND VLLM_FA2_CU_SRCS ${CU_FILE}) # relative to source dir
+    endforeach ()
+
+    # This target automatically depends on the copy by depending on copied files
     define_gpu_extension_target(
             _vllm_fa2_C
             DESTINATION vllm_flash_attn
             LANGUAGE ${VLLM_GPU_LANG}
             SOURCES
-            # csrc/flash_attn_ck/flash_api.cu # only contains declarations & PyBind
             csrc/flash_attn_ck/flash_api_torch_lib.cpp
-            csrc/flash_attn_ck/flash_common.cu
-            csrc/flash_attn_ck/mha_bwd.cu
-            csrc/flash_attn_ck/mha_fwd_kvcache.cu
-            csrc/flash_attn_ck/mha_fwd.cu
-            csrc/flash_attn_ck/mha_varlen_bwd.cu
-            csrc/flash_attn_ck/mha_varlen_fwd.cu
+            ${VLLM_FA2_CU_SRCS}
             ${FA3_GEN_SRCS_CU}
             COMPILE_FLAGS ${VLLM_FA_GPU_FLAGS}
             USE_SABI 3