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[libclc] Skip opt command if opt_flags is empty #130882

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[libclc] Skip opt command if opt_flags is empty #130882

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[libclc] Skip opt command if opt_flags is empty
wenju-he Mar 12, 2025
d3543f3
unconditionally add builtins_opt_lib_tgt, which is empty if OPT_FLAGS…
wenju-he Mar 18, 2025
e02feed
update comment
wenju-he Mar 18, 2025
cb61d08
refine
wenju-he Mar 18, 2025
e7cecc2
unify PROPERTIES FOLDER
wenju-he Mar 18, 2025
36ea924
NOT ARG_OPT_FLAGS
wenju-he Mar 20, 2025
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34 changes: 22 additions & 12 deletions libclc/cmake/modules/AddLibclc.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -342,22 +342,32 @@ function(add_libclc_builtin_set)

set( builtins_opt_lib_tgt builtins.opt.${ARG_ARCH_SUFFIX} )

# Add opt target
add_custom_command( OUTPUT ${builtins_opt_lib_tgt}.bc
COMMAND ${opt_exe} ${ARG_OPT_FLAGS} -o ${builtins_opt_lib_tgt}.bc
${builtins_link_lib}
DEPENDS ${opt_target} ${builtins_link_lib} ${builtins_link_lib_tgt}
)
add_custom_target( ${builtins_opt_lib_tgt}
ALL DEPENDS ${builtins_opt_lib_tgt}.bc
)
if( ${ARG_OPT_FLAGS} STREQUAL "" )
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@frasercrmck frasercrmck Mar 20, 2025

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I just realised this code isn't triggered upstream. I take it you have a downstream making use of it?

I tried it locally and this needs to be if( "${ARG_OPT_FLAGS} STREQUAL "" ) or maybe better yet if ( NOT ARG_OPT_FLAGS ). The code as-is generates an error if I pass in an empty OPT_FLAGS:

CMake Error at /llvm-project/libclc/cmake/modules/AddLibclc.cmake:345 (if):
  if given arguments:

    "STREQUAL" ""

  Unknown arguments specified

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@wenju-he wenju-he Mar 20, 2025 •
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I just realised this code isn't triggered upstream. I take it you have a downstream making use of it?

there is a case in upstream LLVM that opt flag is empty:

llvm-project/libclc/CMakeLists.txt

Line 353 in ad5cac3

set( opt_flags )

I tried it locally and this needs to be if( "${ARG_OPT_FLAGS} STREQUAL "" ) or maybe better yet if ( NOT ARG_OPT_FLAGS ). The code as-is generates an error if I pass in an empty OPT_FLAGS:

CMake Error at /llvm-project/libclc/cmake/modules/AddLibclc.cmake:345 (if):
  if given arguments:

    "STREQUAL" ""

  Unknown arguments specified

Thanks for the testing. Changed to if ( NOT ARG_OPT_FLAGS )
I don't know what happened, a few days ago I did observe that bitcode size become smaller or larger when opt flag is empty.

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@wenju-he wenju-he Mar 20, 2025

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I remembered. I was testing for amdgpu arch. I just switched the code between if and else blocks for testing, and didn't set opt_flags to empty. So the check was wrong at the beginning.

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@frasercrmck frasercrmck Mar 21, 2025

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That's true about SPIR-V, but those targets exit early before we reach the opt target.

If there's no plan for this code to be used in production, I'm not sure it's worth adding this extra logic which needs to be maintained. If it's just for being played around with in testing then the extra time it takes to build isn't so bad? Unless I'm misunderstanding the problem?

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@wenju-he wenju-he Mar 21, 2025

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just curious would this Pr unifies the this code and avoid the early exit and duplicate code for prepare target?

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@wenju-he wenju-he Mar 22, 2025

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let me know if it worth to update PR to unifies the code path and avoids early exit. Otherwise I'll close this PR.

The original request of this PR is to disable opt -O3. But things has changed and the request is irrelevant.
Though in practice it might still make sense to apply the PR to avoid code diverge like for SPIR-V.

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@frasercrmck frasercrmck Mar 24, 2025

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Yes, that might be good actually. Then if SPIR-V did ever want to apply optimizations, it could do so, and it ensures this path is tested.

Note though we'd still need the special-case after the opt target, because SPIR-V will continue to want to run llvm-spirv and exit. It also doesn't run the ${prepare_builtins_exe} utility so needs to exit before that point. I don't know enough about prepare-builtins to say whether SPIR-V could also make use of it: it seems to strip opencl.ocl.version metadata and set every external definition to linkonce_odr linkage. I'd need to investigate what's going on there.

# Add empty opt target.
add_custom_target( ${builtins_opt_lib_tgt} ALL )
add_dependencies( ${builtins_opt_lib_tgt} ${builtins_link_lib_tgt} )

set( builtins_opt_lib ${builtins_link_lib} )
else()
# Add opt target
add_custom_command( OUTPUT ${builtins_opt_lib_tgt}.bc
COMMAND ${opt_exe} ${ARG_OPT_FLAGS} -o ${builtins_opt_lib_tgt}.bc
${builtins_link_lib}
DEPENDS ${opt_target} ${builtins_link_lib} ${builtins_link_lib_tgt}
)
add_custom_target( ${builtins_opt_lib_tgt}
ALL DEPENDS ${builtins_opt_lib_tgt}.bc
)
set_target_properties( ${builtins_opt_lib_tgt} PROPERTIES
TARGET_FILE ${CMAKE_CURRENT_BINARY_DIR}/${builtins_opt_lib_tgt}.bc
)

set( builtins_opt_lib $<TARGET_PROPERTY:${builtins_opt_lib_tgt},TARGET_FILE> )
endif()
set_target_properties( ${builtins_opt_lib_tgt} PROPERTIES
TARGET_FILE ${CMAKE_CURRENT_BINARY_DIR}/${builtins_opt_lib_tgt}.bc
FOLDER "libclc/Device IR/Opt"
)

set( builtins_opt_lib $<TARGET_PROPERTY:${builtins_opt_lib_tgt},TARGET_FILE> )

# Add prepare target
set( obj_suffix ${ARG_ARCH_SUFFIX}.bc )
add_custom_command( OUTPUT ${obj_suffix}
Expand Down