The following adds X86_TUNE_AVX512_TWO_EPILOGUES tuning and directs the
vectorizer to produce both a vector AVX2 and SSE epilogue for AVX512
vectorized loops when set. The tuning is enabled by default for Zen4
and Zen5 where I benchmarked it to be overall positive on SPEC CPU 2017 both
in performance and overall code size. In particular it speeds up
525.x264_r which with only an AVX2 epilogue ends up in unvectorized code
at the moment.
Re-bootstrap and regtest running on x86_64-unknown-linux-gnu
(I've added znver4 to the defaults after benchmarking there and have
to double-check no -mtune=znver4 testcase is affected). Note that
znver4|znver5 is all AMD CPUs with AVX512.
I did not do any benchmarking on Intel CPUs with AVX512 but I do
expect 525.x264_r to improve there as well.
OK for trunk if testing succeeds?
Thanks,
Richard.
* config/i386/i386.cc (ix86_vector_costs::finish_cost): Set
m_suggested_epilogue_mode according to X86_TUNE_AVX512_TWO_EPILOGUES.
* config/i386/x86-tune.def (X86_TUNE_AVX512_TWO_EPILOGUES): Add.
Enable for znver4 and znver5.
---
gcc/config/i386/i386.cc | 12 ++++++++++++
gcc/config/i386/x86-tune.def | 5 +++++
2 files changed, 17 insertions(+)
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 6ac3a5d55f2..526c9df7618 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -25353,6 +25353,18 @@ ix86_vector_costs::finish_cost (const vector_costs
*scalar_costs)
&& TARGET_AVX256_AVOID_VEC_PERM)
m_costs[i] = INT_MAX;
+ /* When X86_TUNE_AVX512_TWO_EPILOGUES is enabled arrange for both
+ a AVX2 and a SSE epilogue for AVX512 vectorized loops. */
+ if (loop_vinfo
+ && ix86_tune_features[X86_TUNE_AVX512_TWO_EPILOGUES])
+ {
+ if (GET_MODE_SIZE (loop_vinfo->vector_mode) == 64)
+ m_suggested_epilogue_mode = V32QImode;
+ else if (LOOP_VINFO_EPILOGUE_P (loop_vinfo)
+ && GET_MODE_SIZE (loop_vinfo->vector_mode) == 32)
+ m_suggested_epilogue_mode = V16QImode;
+ }
+
vector_costs::finish_cost (scalar_costs);
}
diff --git a/gcc/config/i386/x86-tune.def b/gcc/config/i386/x86-tune.def
index 6ebb2fd3414..6bbfc3c3b90 100644
--- a/gcc/config/i386/x86-tune.def
+++ b/gcc/config/i386/x86-tune.def
@@ -597,6 +597,11 @@ DEF_TUNE (X86_TUNE_AVX512_MOVE_BY_PIECES,
"avx512_move_by_pieces",
DEF_TUNE (X86_TUNE_AVX512_STORE_BY_PIECES, "avx512_store_by_pieces",
m_SAPPHIRERAPIDS | m_ZNVER4 | m_ZNVER5)
+/* X86_TUNE_AVX512_TWO_EPILOGUES: Use two vector epilogues for 512-bit
+ vectorized loops. */
+DEF_TUNE (X86_TUNE_AVX512_TWO_EPILOGUES, "avx512_two_epilogues",
+ m_ZNVER5)
+
/*****************************************************************************/
/*****************************************************************************/
/* Historical relics: tuning flags that helps a specific old CPU designs */
--
2.43.0
