[PATCH] xtensa: Optimize integer constant addition that is between -32896 and 32639

[PATCH] xtensa: Optimize integer constant addition that is between -32896 and 32639

[Takayuki 'January June' Suwa]

Such constants are often subject to the constant synthesis:

    int test(int a) {
      return a - 31999;
    }

    test:
	movi	a3, 1
	addmi	a3, a3, -0x7d00
	add	a2, a2, a3
	ret

This patch optimizes such case as follows:

    test:
	addi	a2, a2, 1
	addmi	a2, a2, -0x7d00
	ret

gcc/ChangeLog:

	* config/xtensa/xtensa.md:
	Suppress unnecessary emitting nop insn in the split patterns for
	integer/FP constant synthesis, and add new peephole2 pattern that
	folds such synthesized additions.
---
 gcc/config/xtensa/xtensa.md | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md
index f31ec33b362..9d998589631 100644
--- a/gcc/config/xtensa/xtensa.md
+++ b/gcc/config/xtensa/xtensa.md
@@ -1033,6 +1033,7 @@
     FAIL;
   if (! xtensa_constantsynth (operands[0], INTVAL (x)))
     emit_move_insn (operands[0], x);
+  DONE;
 })
 
 ;; 16-bit Integer moves
@@ -1272,6 +1273,7 @@
   x = gen_rtx_REG (SImode, REGNO (operands[0]));
   if (! xtensa_constantsynth (x, l[i]))
     emit_move_insn (x, GEN_INT (l[i]));
+  DONE;
 })
 
 ;; 64-bit floating point moves
@@ -2808,3 +2810,36 @@
 	 && REGNO (x) == regno + REG_NREGS (operands[0]) / 2))
     FAIL;
 })
+
+(define_peephole2
+  [(set (match_operand:SI 0 "register_operand")
+	(match_operand:SI 1 "const_int_operand"))
+   (set (match_dup 0)
+	(plus:SI (match_dup 0)
+		 (match_operand:SI 2 "const_int_operand")))
+   (set (match_operand:SI 3 "register_operand")
+	(plus:SI (match_operand:SI 4 "register_operand")
+		 (match_dup 0)))]
+  "IN_RANGE (INTVAL (operands[1]) + INTVAL (operands[2]),
+	     (-128 - 32768), (127 + 32512))
+   && REGNO (operands[0]) != REGNO (operands[3])
+   && REGNO (operands[0]) != REGNO (operands[4])
+   && peep2_reg_dead_p (3, operands[0])"
+  [(set (match_dup 3)
+	(plus:SI (match_dup 4)
+		 (match_dup 1)))
+   (set (match_dup 3)
+	(plus:SI (match_dup 3)
+		 (match_dup 2)))]
+{
+  HOST_WIDE_INT value = INTVAL (operands[1]) + INTVAL (operands[2]);
+  int imm0, imm1;
+  value += 128;
+  if (value > 32512)
+    imm1 = 32512;
+  else
+    imm1 = value & ~255;
+  imm0 = value - imm1 - 128;
+  operands[1] = GEN_INT (imm0);
+  operands[2] = GEN_INT (imm1);
+})
-- 
2.20.1

Re: [PATCH] xtensa: Optimize integer constant addition that is between -32896 and 32639

[Max Filippov]

On Sun, Jun 26, 2022 at 7:53 AM Takayuki 'January June' Suwa
<jjsuwa_sys3175@yahoo.co.jp> wrote:
>
> Such constants are often subject to the constant synthesis:
>
>     int test(int a) {
>       return a - 31999;
>     }
>
>     test:
>         movi    a3, 1
>         addmi   a3, a3, -0x7d00
>         add     a2, a2, a3
>         ret
>
> This patch optimizes such case as follows:
>
>     test:
>         addi    a2, a2, 1
>         addmi   a2, a2, -0x7d00
>         ret
>
> gcc/ChangeLog:
>
>         * config/xtensa/xtensa.md:
>         Suppress unnecessary emitting nop insn in the split patterns for
>         integer/FP constant synthesis, and add new peephole2 pattern that
>         folds such synthesized additions.
> ---
>  gcc/config/xtensa/xtensa.md | 35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)

Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.

-- 
Thanks.
-- Max