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gh-129987: Selectively re-enable SLP autovectorization of _PyEval_EvalFrameDefault #132530

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Merged
merged 2 commits into from
Apr 15, 2025
+8 −4
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gh-129987: Selectively re-enable SLP autovectorization of _PyEval_EvalFrameDefault #132530

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087f134
Only disable SLP autovectorization of `_PyEval_EvalFrameDefault` on n…
Yhg1s Apr 14, 2025
fc53ffe
Add comment linking to the likely culprit in GCC.
Yhg1s Apr 15, 2025
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12 changes: 8 additions & 4 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -948,11 +948,15 @@ _PyObjectArray_Free(PyObject **array, PyObject **scratch)
#include "generated_cases.c.h"
#endif

#if (defined(__GNUC__) && !defined(__clang__)) && defined(__x86_64__)
#if (defined(__GNUC__) && __GNUC__ >= 10 && !defined(__clang__)) && defined(__x86_64__)
/*
* gh-129987: The SLP autovectorizer can cause poor code generation for opcode
* dispatch, negating any benefit we get from vectorization elsewhere in the
* interpreter loop.
* gh-129987: The SLP autovectorizer can cause poor code generation for
* opcode dispatch in some GCC versions (observed in GCCs 12 through 15,
* probably caused by https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115777),
* negating any benefit we get from vectorization elsewhere in the
* interpreter loop. Disabling it significantly affected older GCC versions
* (prior to GCC 9, 40% performance drop), so we have to selectively disable
* it.
*/
#define DONT_SLP_VECTORIZE __attribute__((optimize ("no-tree-slp-vectorize")))
#else
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