This is a known (but poorly documented) issue. Please can you raise a
bug on this?
On 05/06/2019 18:43, Max Marrone via cfe-users wrote:
The docs for llvm-mca
<https://llvm.org/docs/CommandGuide/llvm-mca.html#using-markers-to-analyze-specific-code-blocks> suggest
using inline assembly to mark the region that llvm-mca should examine,
i.e.
__asm volatile("# LLVM-MCA-BEGIN");
// ...
__asm volatile("# LLVM-MCA-END");
However, these directives seem to interfere with auto-vectorization.
<source>:8:3: remark: loop not vectorized: call instruction cannot be
vectorized [-Rpass-analysis=loop-vectorize]
__asm volatile("# LLVM-MCA-BEGIN sum_marked");
^
<source>:6:2: remark: loop not vectorized: read with atomic ordering
or volatile read [-Rpass-analysis=loop-vectorize]
for (size_t index = 0; index < count; index++)
^
<https://godbolt.org/z/NSQchu>
Compiler Explorer link. <https://godbolt.org/z/NSQchu>
Any ideas for a workaround, other than compiling unmarked source and
then manually inserting markers into the emitted assembly?
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