MOVE_MAX on x86* used to accept up to 16 bytes, even without SSE,
which enabled inlining of small memmove by loading and then storing
the entire range. After the "x86: Update piecewise move and store"
r12-2666 change, memmove of more than 4 bytes would not be inlined in
gimple_fold_bultin_memory_op, failing the expectations of a few tests.
I can see how lowering it for MOVE_MAX_PIECES can get us better
codegen decisions overall, but surely inlining memmove with 2 32-bit
loads and stores is better than an outline call that requires setting
up 3 arguments. I suppose even 3 or 4 could do better. But maybe it
is gimple_fold_builtin_memory_op that needs tweaking?
Anyhow, this patch raises MOVE_MAX back a little for non-SSE targets,
while preserving the new value for MOVE_MAX_PIECES.
Bootstrapped on x86_64-linux-gnu. Also tested on ppc- and x86-vx7r2
with gcc-12.
for gcc/ChangeLog
* config/i386/i386.h (MOVE_MAX): Rename to...
(MOVE_MAX_VEC): ... this. Add NONVEC parameter, and use it as
the last resort, instead of UNITS_PER_WORD.
(MOVE_MAX): Reintroduce in terms of MOVE_MAX_VEC, with
2*UNITS_PER_WORD.
(MOVE_MAX_PIECES): Likewise, but with UNITS_PER_WORD.
---
gcc/config/i386/i386.h | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/gcc/config/i386/i386.h b/gcc/config/i386/i386.h
index c7439f89bdf92..5293a332a969a 100644
--- a/gcc/config/i386/i386.h
+++ b/gcc/config/i386/i386.h
@@ -1801,7 +1801,9 @@ typedef struct ix86_args {
is the number of bytes at a time which we can move efficiently.
MOVE_MAX_PIECES defaults to MOVE_MAX. */
-#define MOVE_MAX \
+#define MOVE_MAX MOVE_MAX_VEC (2 * UNITS_PER_WORD)
+#define MOVE_MAX_PIECES MOVE_MAX_VEC (UNITS_PER_WORD)
+#define MOVE_MAX_VEC(NONVEC) \
((TARGET_AVX512F \
&& (ix86_move_max == PVW_AVX512 \
|| ix86_store_max == PVW_AVX512)) \
@@ -1813,7 +1815,7 @@ typedef struct ix86_args {
: ((TARGET_SSE2 \
&& TARGET_SSE_UNALIGNED_LOAD_OPTIMAL \
&& TARGET_SSE_UNALIGNED_STORE_OPTIMAL) \
- ? 16 : UNITS_PER_WORD)))
+ ? 16 : (NONVEC))))
/* STORE_MAX_PIECES is the number of bytes at a time that we can store
efficiently. Allow 16/32/64 bytes only if inter-unit move is enabled
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
