[PATCH] D96769: [OpenMP][AMDGPU] Skip backend and assemble phases for amdgcn

Wed Feb 17 14:33:44 PST 2021

JonChesterfield added a comment.

Debugged this because I need save-temps (or hack up a binary by hand) to debug something else. The problem is addClangTargetOptions gets called to add target options to clang. With save temps, an early clang invocation runs the preprocessor alone. That gets passed the target specific flags, something like:

  "clang-13" "-cc1" "-mllvm" "--amdhsa-code-object-version=3" "-triple" "amdgcn-amd-amdhsa" "-aux-triple" "x86_64-pc-linux-gnu" "-E" "-save-temps=cwd" "-disable-free" "-main-file-name" "firstprivate.c" "-target-cpu" "gfx906" "-fcuda-is-device" "-emit-llvm-bc" "-mlink-builtin-bitcode" "/home/amd/llvm-install/lib/libomptarget-amdgcn-gfx906.bc" "-fno-split-dwarf-inlining" "-debugger-tuning=gdb" "-O2" "-fdebug-compilation-dir" "/home/amd/aomp/aomp/test/smoke/firstprivate" "-ferror-limit" "19" "-fmessage-length=102" "-fopenmp" "-fopenmp-cuda-parallel-target-regions" "-fgnuc-version=4.2.1" "-fopenmp-is-device" "-munsafe-fp-atomics" "-faddrsig" "-o" "firstprivate-openmp-amdgcn-amd-amdhsa.i" "-x" "c" "firstprivate.c"

Deleted some parts of that. The "-E" gives preprocessor behaviour. Things like -O2 or munsafe-fp-atomics don't matter to the preprocessor but are passed anyway, so there's prior art for it ignoring arguments when called as save temps. Whichever of emit-llvm-bc and E comes last wins, and the target options come after the E, so currently clang emits (binary) bytecode which is later interpreted as cpp-output, which can't handle bytecode.

With this patch applied, the problem of overriding the E flag is sidestepped. There are alternatives, but this approach looks cleaner than the others I can think of.

Note that it isn't a complete fix for save-temps, but it gets me as far as `multiple definition of `__dummy.omp_offloading.entry'`, which I vaguely remember marking as a weak symbol for the aomp toolchain. It lets clang get as far as emitting the device binary I wanted access to, so I'm now very sure this patch works.

Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D96769