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i386: Use xor to write zero to memory with -Os even for more than 4 stores [PR11877]

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> > 2021-06-20  Roger Sayle  <roger@nextmovesoftware.com>
> >
> > gcc/ChangeLog
> >         PR target/11877
> >         * config/i386/i386.md: New define_peephole2s to shrink writing
> >         1, 2 or 4 consecutive zeros to memory when optimizing for size.

It unfortunately doesn't extend well to larger memory clearing.
Consider e.g.
void
foo (int *p)
{
  p[0] = 0;
  p[7] = 0;
  p[23] = 0;
  p[41] = 0;
  p[48] = 0;
  p[59] = 0;
  p[69] = 0;
  p[78] = 0;
  p[83] = 0;
  p[89] = 0;
  p[98] = 0;
  p[121] = 0;
  p[132] = 0;
  p[143] = 0;
  p[154] = 0;
}
where with the patch we emit:
        xorl    %eax, %eax
        xorl    %edx, %edx
        xorl    %ecx, %ecx
        xorl    %esi, %esi
        xorl    %r8d, %r8d
        movl    %eax, (%rdi)
        movl    %eax, 28(%rdi)
        movl    %eax, 92(%rdi)
        movl    %eax, 164(%rdi)
        movl    %edx, 192(%rdi)
        movl    %edx, 236(%rdi)
        movl    %edx, 276(%rdi)
        movl    %edx, 312(%rdi)
        movl    %ecx, 332(%rdi)
        movl    %ecx, 356(%rdi)
        movl    %ecx, 392(%rdi)
        movl    %ecx, 484(%rdi)
        movl    %esi, 528(%rdi)
        movl    %esi, 572(%rdi)
        movl    %r8d, 616(%rdi)
Here is an incremental patch that emits:
        xorl    %eax, %eax
        movl    %eax, (%rdi)
        movl    %eax, 28(%rdi)
        movl    %eax, 92(%rdi)
        movl    %eax, 164(%rdi)
        movl    %eax, 192(%rdi)
        movl    %eax, 236(%rdi)
        movl    %eax, 276(%rdi)
        movl    %eax, 312(%rdi)
        movl    %eax, 332(%rdi)
        movl    %eax, 356(%rdi)
        movl    %eax, 392(%rdi)
        movl    %eax, 484(%rdi)
        movl    %eax, 528(%rdi)
        movl    %eax, 572(%rdi)
        movl    %eax, 616(%rdi)
instead.

2021-06-22  Jakub Jelinek  <jakub@redhat.com>

	PR target/11877
	* config/i386/i386-protos.h (ix86_last_zero_store_uid): Declare.
	* config/i386/i386-expand.c (ix86_last_zero_store_uid): New variable.
	* config/i386/i386.c (ix86_expand_prologue): Clear it.
	* config/i386/i386.md (peephole2s for 1/2/4 stores of const0_rtx):
	Remove "" from match_operand.  Emit new insns using emit_move_insn and
	set ix86_last_zero_store_uid to INSN_UID of the last store.
	Add peephole2s for 1/2/4 stores of const0_rtx following previous
	successful peep2s.

	* gcc.target/i386/pr11877-2.c: New test.
This commit is contained in:
Jakub Jelinek 2021-06-22 10:16:18 +02:00
parent 706533c339
commit d58a66aa0f
5 changed files with 104 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
gcc/config/i386/i386-expand.c
View File

@ -1316,6 +1316,9 @@ find_nearest_reg_def (rtx_insn *insn, int regno1, int regno2)
return false;
}
/* INSN_UID of the last insn emitted by zero store peephole2s. */
int ix86_last_zero_store_uid;
/* Split lea instructions into a sequence of instructions
which are executed on ALU to avoid AGU stalls.
It is assumed that it is allowed to clobber flags register

1
gcc/config/i386/i386-protos.h
View File

@ -111,6 +111,7 @@ extern bool ix86_use_lea_for_mov (rtx_insn *, rtx[]);
extern bool ix86_avoid_lea_for_addr (rtx_insn *, rtx[]);
extern void ix86_split_lea_for_addr (rtx_insn *, rtx[], machine_mode);
extern bool ix86_lea_for_add_ok (rtx_insn *, rtx[]);
extern int ix86_last_zero_store_uid;
extern bool ix86_vec_interleave_v2df_operator_ok (rtx operands[3], bool high);
extern bool ix86_dep_by_shift_count (const_rtx set_insn, const_rtx use_insn);
extern bool ix86_agi_dependent (rtx_insn *set_insn, rtx_insn *use_insn);

1
gcc/config/i386/i386.c
View File

@ -8196,6 +8196,7 @@ ix86_expand_prologue (void)
bool save_stub_call_needed;
rtx static_chain = NULL_RTX;
ix86_last_zero_store_uid = 0;
if (ix86_function_naked (current_function_decl))
{
if (flag_stack_usage_info)

87
gcc/config/i386/i386.md
View File

@ -19360,37 +19360,96 @@
;; When optimizing for size, zeroing memory should use a register.
(define_peephole2
[(match_scratch:SWI48 0 "r")
(set (match_operand:SWI48 1 "memory_operand" "") (const_int 0))
(set (match_operand:SWI48 2 "memory_operand" "") (const_int 0))
(set (match_operand:SWI48 3 "memory_operand" "") (const_int 0))
(set (match_operand:SWI48 4 "memory_operand" "") (const_int 0))]
(set (match_operand:SWI48 1 "memory_operand") (const_int 0))
(set (match_operand:SWI48 2 "memory_operand") (const_int 0))
(set (match_operand:SWI48 3 "memory_operand") (const_int 0))
(set (match_operand:SWI48 4 "memory_operand") (const_int 0))]
"optimize_insn_for_size_p () && peep2_regno_dead_p (0, FLAGS_REG)"
[(set (match_dup 1) (match_dup 0))
(set (match_dup 2) (match_dup 0))
(set (match_dup 3) (match_dup 0))
(set (match_dup 4) (match_dup 0))]
[(const_int 0)]
{
ix86_expand_clear (operands[0]);
emit_move_insn (operands[1], operands[0]);
emit_move_insn (operands[2], operands[0]);
emit_move_insn (operands[3], operands[0]);
ix86_last_zero_store_uid
= INSN_UID (emit_move_insn (operands[4], operands[0]));
DONE;
})
(define_peephole2
[(match_scratch:SWI48 0 "r")
(set (match_operand:SWI48 1 "memory_operand" "") (const_int 0))
(set (match_operand:SWI48 2 "memory_operand" "") (const_int 0))]
(set (match_operand:SWI48 1 "memory_operand") (const_int 0))
(set (match_operand:SWI48 2 "memory_operand") (const_int 0))]
"optimize_insn_for_size_p () && peep2_regno_dead_p (0, FLAGS_REG)"
[(set (match_dup 1) (match_dup 0))
(set (match_dup 2) (match_dup 0))]
[(const_int 0)]
{
ix86_expand_clear (operands[0]);
emit_move_insn (operands[1], operands[0]);
ix86_last_zero_store_uid
= INSN_UID (emit_move_insn (operands[2], operands[0]));
DONE;
})
(define_peephole2
[(match_scratch:SWI48 0 "r")
(set (match_operand:SWI48 1 "memory_operand" "") (const_int 0))]
(set (match_operand:SWI48 1 "memory_operand") (const_int 0))]
"optimize_insn_for_size_p () && peep2_regno_dead_p (0, FLAGS_REG)"
[(set (match_dup 1) (match_dup 0))]
[(const_int 0)]
{
ix86_expand_clear (operands[0]);
ix86_last_zero_store_uid
= INSN_UID (emit_move_insn (operands[1], operands[0]));
DONE;
})
(define_peephole2
[(set (match_operand:SWI48 5 "memory_operand")
(match_operand:SWI48 0 "general_reg_operand"))
(set (match_operand:SWI48 1 "memory_operand") (const_int 0))
(set (match_operand:SWI48 2 "memory_operand") (const_int 0))
(set (match_operand:SWI48 3 "memory_operand") (const_int 0))
(set (match_operand:SWI48 4 "memory_operand") (const_int 0))]
"optimize_insn_for_size_p ()
&& INSN_UID (peep2_next_insn (0)) == ix86_last_zero_store_uid"
[(const_int 0)]
{
emit_move_insn (operands[5], operands[0]);
emit_move_insn (operands[1], operands[0]);
emit_move_insn (operands[2], operands[0]);
emit_move_insn (operands[3], operands[0]);
ix86_last_zero_store_uid
= INSN_UID (emit_move_insn (operands[4], operands[0]));
DONE;
})
(define_peephole2
[(set (match_operand:SWI48 3 "memory_operand")
(match_operand:SWI48 0 "general_reg_operand"))
(set (match_operand:SWI48 1 "memory_operand") (const_int 0))
(set (match_operand:SWI48 2 "memory_operand") (const_int 0))]
"optimize_insn_for_size_p ()
&& INSN_UID (peep2_next_insn (0)) == ix86_last_zero_store_uid"
[(const_int 0)]
{
emit_move_insn (operands[3], operands[0]);
emit_move_insn (operands[1], operands[0]);
ix86_last_zero_store_uid
= INSN_UID (emit_move_insn (operands[2], operands[0]));
DONE;
})
(define_peephole2
[(set (match_operand:SWI48 2 "memory_operand")
(match_operand:SWI48 0 "general_reg_operand"))
(set (match_operand:SWI48 1 "memory_operand") (const_int 0))]
"optimize_insn_for_size_p ()
&& INSN_UID (peep2_next_insn (0)) == ix86_last_zero_store_uid"
[(const_int 0)]
{
emit_move_insn (operands[2], operands[0]);
ix86_last_zero_store_uid
= INSN_UID (emit_move_insn (operands[1], operands[0]));
DONE;
})
;; Reload dislikes loading constants directly into class_likely_spilled

26
gcc/testsuite/gcc.target/i386/pr11877-2.c Normal file
View File

@ -0,0 +1,26 @@
/* PR target/11877 */
/* { dg-do compile } */
/* { dg-options "-Os" } */
void
foo (int *p)
{
p[0] = 0;
p[7] = 0;
p[23] = 0;
p[41] = 0;
p[48] = 0;
p[59] = 0;
p[69] = 0;
p[78] = 0;
p[83] = 0;
p[89] = 0;
p[98] = 0;
p[121] = 0;
p[132] = 0;
p[143] = 0;
p[154] = 0;
}
/* { dg-final { scan-assembler-times "xorl\[ \t\]" 1 } } */
/* { dg-final { scan-assembler-not "\\\$0," } } */