[PATCH] [x86] reenable dword MOVE_MAX for better memmove inlining

[Alexandre Oliva <oliva@adacore.com>]

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
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