Fix tablegen cmake rule.

[jyknight]

Summary

Fix tablegen's PrintFatalError function to run registered file cleanups.

Also, change code in tablegen which printed a message and then called
"exit(1)" to use PrintFatalError, instead.

This fixes instances where an empty output file was left behind after
a failed tablegen invocation, which would confuse subsequent ninja
runs into not attempting to rebuild.

[rnk]

TableGen is supposed to ensure that the output file is deleted after a non-zero exit, even if it crashes. See lib/TableGen/Main.cpp and look for tool_output_file. Is our signal handler failing somehow? It might be worth debugging that. I know the signal handler is already super async-unsafe, but we should be able to limp along well enough to delete an output file.

cmake/modules/TableGen.cmake

31–32

I would be surprised if this shell expression works on Windows. =/

[jyknight]

Okay, right, I'll look into fixing it within the tool instead of this.

cmake/modules/TableGen.cmake

31–32

Er, damnit, Windows, forgot about that.

[jyknight]

Looks like it doesn't have an atexit handler to call the cleanup function, only a signal handler. And PrintFatalError just calls exit(1), which doesn't unwind the stack to call destructors. So, the cleanup never happens.

[jyknight]

Rework, fixing tablegen binary instead of hacking cmake rule.

[rnk]

lgtm

Ouch, so much exit(1)... Anyway, this is consistent with report_fatal_error, which is the non-tablegen analogue for this.

cmake/modules/TableGen.cmake

else()
     set(LLVM_TARGET_DEFINITIONS_ABSOLUTE
       ${CMAKE_CURRENT_SOURCE_DIR}/${LLVM_TARGET_DEFINITIONS})
   endif()
   add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
     # Generate tablegen output in a temporary file.
     COMMAND ${${project}_TABLEGEN_EXE} ${ARGN} -I ${CMAKE_CURRENT_SOURCE_DIR}
     -I ${LLVM_MAIN_SRC_DIR}/lib/Target -I ${LLVM_MAIN_INCLUDE_DIR}
     ${LLVM_TARGET_DEFINITIONS_ABSOLUTE}
-    -o ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
+    -o ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp ||
+    { rm -f ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp && false \; }
     # The file in LLVM_TARGET_DEFINITIONS may be not in the current
     # directory and local_tds may not contain it, so we must
     # explicitly list it here:
     DEPENDS ${${project}_TABLEGEN_TARGET} ${local_tds} ${global_tds}
     ${LLVM_TARGET_DEFINITIONS_ABSOLUTE}
     COMMENT "Building ${ofn}..."
     )
   add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}