On Thu, Apr 12, 2018 at 05:29:35PM +0000, Wilco Dijkstra wrote:
> > Depending on what you mean old, I see e.g. in 2010 power7 mempcpy got added,
> > in 2013 other power versions, in 2016 s390*, etc. Doing a decent mempcpy
> > isn't hard if you have asm version of memcpy and one spare register.
>
> More mempcpy implementations have been added in recent years indeed, but
> almost all
> add an extra copy of the memcpy code rather than using a single combined
> implementation.
> That means it is still better to call memcpy (which is frequently used and
> thus likely in L1/L2)
> rather than mempcpy (which is more likely to be cold and thus not cached).
That really depends, usually when some app uses mempcpy, it uses it very
heavily. And all the proposed patches do is honor what the user asked, if
you use memcpy () + n, we aren't transforming that into mempcpy behind the
user's back.
Anyway, here is what I think Richard was asking for, that I'm currently
bootstrapping/regtesting. It can be easily combined with Martin's target
hook if needed, or do it only for
endp == 1 && target != const0_rtx && CALL_EXPR_TAILCALL (exp)
etc.
2018-04-12 Martin Liska <mli...@suse.cz>
Jakub Jelinek <ja...@redhat.com>
PR middle-end/81657
* expr.h (enum block_op_methods): Add BLOCK_OP_NO_LIBCALL_RET.
* expr.c (emit_block_move_hints): Handle BLOCK_OP_NO_LIBCALL_RET.
* builtins.c (expand_builtin_memory_copy_args): Use
BLOCK_OP_NO_LIBCALL_RET method for mempcpy with non-ignored target,
handle dest_addr == pc_rtx.
* gcc.dg/string-opt-1.c: Remove bogus comment. Expect a mempcpy
call.
--- gcc/expr.h.jj 2018-01-12 11:35:51.424222835 +0100
+++ gcc/expr.h 2018-04-12 18:38:07.377464114 +0200
@@ -100,7 +100,11 @@ enum block_op_methods
BLOCK_OP_NO_LIBCALL,
BLOCK_OP_CALL_PARM,
/* Like BLOCK_OP_NORMAL, but the libcall can be tail call optimized. */
- BLOCK_OP_TAILCALL
+ BLOCK_OP_TAILCALL,
+ /* Like BLOCK_OP_NO_LIBCALL, but instead of emitting a libcall return
+ pc_rtx to indicate nothing has been emitted and let the caller handle
+ it. */
+ BLOCK_OP_NO_LIBCALL_RET
};
typedef rtx (*by_pieces_constfn) (void *, HOST_WIDE_INT, scalar_int_mode);
--- gcc/expr.c.jj 2018-04-06 19:19:14.954130838 +0200
+++ gcc/expr.c 2018-04-12 18:39:58.866536619 +0200
@@ -1565,7 +1565,7 @@ emit_block_move_hints (rtx x, rtx y, rtx
unsigned HOST_WIDE_INT max_size,
unsigned HOST_WIDE_INT probable_max_size)
{
- bool may_use_call;
+ int may_use_call;
rtx retval = 0;
unsigned int align;
@@ -1577,7 +1577,7 @@ emit_block_move_hints (rtx x, rtx y, rtx
{
case BLOCK_OP_NORMAL:
case BLOCK_OP_TAILCALL:
- may_use_call = true;
+ may_use_call = 1;
break;
case BLOCK_OP_CALL_PARM:
@@ -1589,7 +1589,11 @@ emit_block_move_hints (rtx x, rtx y, rtx
break;
case BLOCK_OP_NO_LIBCALL:
- may_use_call = false;
+ may_use_call = 0;
+ break;
+
+ case BLOCK_OP_NO_LIBCALL_RET:
+ may_use_call = -1;
break;
default:
@@ -1625,6 +1629,9 @@ emit_block_move_hints (rtx x, rtx y, rtx
&& ADDR_SPACE_GENERIC_P (MEM_ADDR_SPACE (x))
&& ADDR_SPACE_GENERIC_P (MEM_ADDR_SPACE (y)))
{
+ if (may_use_call < 0)
+ return pc_rtx;
+
/* Since x and y are passed to a libcall, mark the corresponding
tree EXPR as addressable. */
tree y_expr = MEM_EXPR (y);
--- gcc/builtins.c.jj 2018-04-12 13:35:34.328395156 +0200
+++ gcc/builtins.c 2018-04-12 18:42:01.846616598 +0200
@@ -3650,12 +3650,16 @@ expand_builtin_memory_copy_args (tree de
set_mem_align (src_mem, src_align);
/* Copy word part most expediently. */
- dest_addr = emit_block_move_hints (dest_mem, src_mem, len_rtx,
- CALL_EXPR_TAILCALL (exp)
- && (endp == 0 || target == const0_rtx)
- ? BLOCK_OP_TAILCALL : BLOCK_OP_NORMAL,
+ enum block_op_methods method = BLOCK_OP_NORMAL;
+ if (CALL_EXPR_TAILCALL (exp) && (endp == 0 || target == const0_rtx))
+ method = BLOCK_OP_TAILCALL;
+ if (endp == 1 && target != const0_rtx)
+ method = BLOCK_OP_NO_LIBCALL_RET;
+ dest_addr = emit_block_move_hints (dest_mem, src_mem, len_rtx, method,
expected_align, expected_size,
min_size, max_size, probable_max_size);
+ if (dest_addr == pc_rtx)
+ return NULL_RTX;
if (dest_addr == 0)
{
--- gcc/testsuite/gcc.dg/string-opt-1.c.jj 2017-08-01 19:23:09.923512205
+0200
+++ gcc/testsuite/gcc.dg/string-opt-1.c 2018-04-12 18:57:10.940217129 +0200
@@ -1,4 +1,3 @@
-/* Ensure mempcpy is "optimized" into memcpy followed by addition. */
/* { dg-do compile } */
/* { dg-options "-O2" } */
@@ -48,5 +47,5 @@ main (void)
return 0;
}
-/* { dg-final { scan-assembler-not "\<mempcpy\>" } } */
+/* { dg-final { scan-assembler "mempcpy" } } */
/* { dg-final { scan-assembler "memcpy" } } */
Jakub
