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64 lines
2.2 KiB
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64 lines
2.2 KiB
ReStructuredText
==========
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KernelInfo
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==========
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.. contents::
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:local:
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Introduction
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============
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This LLVM IR pass reports various statistics for code compiled for GPUs. The
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goal of these statistics is to help identify bad code patterns and ways to
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mitigate them. The pass operates at the LLVM IR level so that it can, in
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theory, support any LLVM-based compiler for programming languages supporting
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GPUs.
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By default, the pass runs at the end of LTO, and options like
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``-Rpass=kernel-info`` enable its remarks. Example ``opt`` and ``clang``
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command lines appear in the next section.
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Remarks include summary statistics (e.g., total size of static allocas) and
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individual occurrences (e.g., source location of each alloca). Examples of the
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output appear in tests in `llvm/test/Analysis/KernelInfo`.
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Example Command Lines
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=====================
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To analyze a C program as it appears to an LLVM GPU backend at the end of LTO:
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.. code-block:: shell
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$ clang -O2 -g -fopenmp --offload-arch=native test.c -foffload-lto \
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-Rpass=kernel-info
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To analyze specified LLVM IR, perhaps previously generated by something like
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``clang -save-temps -g -fopenmp --offload-arch=native test.c``:
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.. code-block:: shell
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$ opt -disable-output test-openmp-nvptx64-nvidia-cuda-sm_70.bc \
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-pass-remarks=kernel-info -passes=kernel-info
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When specifying an LLVM pass pipeline on the command line, ``kernel-info`` still
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runs at the end of LTO by default. ``-no-kernel-info-end-lto`` disables that
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behavior so you can position ``kernel-info`` explicitly:
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.. code-block:: shell
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$ clang -O2 -g -fopenmp --offload-arch=native test.c -foffload-lto \
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-Rpass=kernel-info \
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-Xoffload-linker --lto-newpm-passes='lto<O2>'
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$ clang -O2 -g -fopenmp --offload-arch=native test.c -foffload-lto \
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-Rpass=kernel-info -mllvm -no-kernel-info-end-lto \
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-Xoffload-linker --lto-newpm-passes='module(kernel-info),lto<O2>'
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$ opt -disable-output test-openmp-nvptx64-nvidia-cuda-sm_70.bc \
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-pass-remarks=kernel-info \
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-passes='lto<O2>'
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$ opt -disable-output test-openmp-nvptx64-nvidia-cuda-sm_70.bc \
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-pass-remarks=kernel-info -no-kernel-info-end-lto \
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-passes='module(kernel-info),lto<O2>'
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