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Diffstat (limited to 'llvm/docs/CommandGuide')
| -rw-r--r-- | llvm/docs/CommandGuide/llvm-mca.rst | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/llvm/docs/CommandGuide/llvm-mca.rst b/llvm/docs/CommandGuide/llvm-mca.rst index 5b30a8a532a..d8c3b57207c 100644 --- a/llvm/docs/CommandGuide/llvm-mca.rst +++ b/llvm/docs/CommandGuide/llvm-mca.rst @@ -241,8 +241,8 @@ Example of overlapping regions: Note that multiple anonymous regions cannot overlap. Also, overlapping regions cannot have the same name. -Inline assembly directives may be used from source code to annotate the -assembly text: +There is no support for marking regions from high-level source code, like C or +C++. As a workaround, inline assembly directives may be used: .. code-block:: c++ @@ -254,6 +254,15 @@ assembly text: return a; } +However, this interferes with optimizations like loop vectorization and may have +an impact on the code generated. This is because the ``__asm`` statements are +seen as real code having important side effects, which limits how the code +around them can be transformed. If users want to make use of inline assembly +to emit markers, then the recommendation is to always verify that the output +assembly is equivalent to the assembly generated in the absence of markers. +The `Clang options to emit optimization reports <https://clang.llvm.org/docs/UsersManual.html#options-to-emit-optimization-reports>`_ +can also help in detecting missed optimizations. + HOW LLVM-MCA WORKS ------------------ |
