https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92448
Bug ID: 92448
Summary: Confusing using of TARGET_PREFER_AVX128
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: crazylht at gmail dot com
CC: hjl.tools at gmail dot com, rguenth at gcc dot gnu.org,
uros at gcc dot gnu.org
Target Milestone: ---
Target: i386, x86-64
In x86 backend, we have 2 macros related to 128-bit vectorization, one is
TARGET_AVX128_OPTIMAL which is a tune option.
--------------------
#define TARGET_AVX128_OPTIMAL \
ix86_tune_features[X86_TUNE_AVX128_OPTIMAL]
/* X86_TUNE_AVX128_OPTIMAL: Enable 128-bit AVX instruction generation for
the auto-vectorizer. */
DEF_TUNE (X86_TUNE_AVX128_OPTIMAL, "avx128_optimal", m_BDVER | m_BTVER2
| m_ZNVER1 | m_CORE_AVX)
-------------------
another is TARGET_PREFER_AVX128
------------------
/* Use 128-bit AVX instructions in the auto-vectorizer. */
#define TARGET_PREFER_AVX128 (prefer_vector_width_type == PVW_AVX128)
-------------------
As my understanding, TARGET_PREFER_AVX128 only related to vector width choosing
in auto vectorization, it shouldn't be used for insntruction generation in md
file.
but I find many using of TARGET_PREFER_AVX128/256 in sse.md and i386.md which
makes it quite confusing.
----------------------
grep --color -nH -e TARGET_PREFER_AVX *.md
i386.md:3534: (not (match_test "TARGET_PREFER_AVX256")))
i386.md:3551: (cond [(and (ior (not (match_test
"TARGET_PREFER_AVX256"))
i386.md:3716: (not (match_test "TARGET_PREFER_AVX256")))
i386.md:3738: (cond [(and (ior (not (match_test
"TARGET_PREFER_AVX256"))
sse.md:7052: if (TARGET_AVX && !TARGET_PREFER_AVX128 &&
optimize_insn_for_speed_p ())
sse.md:7114: if (TARGET_AVX && !TARGET_PREFER_AVX128 &&
optimize_insn_for_speed_p ())
sse.md:7229: if (TARGET_AVX && !TARGET_PREFER_AVX128 &&
optimize_insn_for_speed_p ())
sse.md:17996: && TARGET_AVX && !TARGET_PREFER_AVX128 &&
optimize_insn_for_speed_p ())
sse.md:18128: && TARGET_AVX && !TARGET_PREFER_AVX128 &&
optimize_insn_for_speed_p ())
----------------------
Should we change those TARGET_PREFER_AVX128 to TARGET_AVX128_OPTIMAL in *.md
files? So did TARGET_PREFER_AVX256.
