[PATCH 2/4] xtensa: Make one_cmplsi2 optimizer-friendly

[PATCH 2/4] xtensa: Make one_cmplsi2 optimizer-friendly

[Takayuki 'January June' Suwa]

In Xtensa ISA, there is no single machine instruction that calculates unary
bitwise negation.  But a few optimizers assume that bitwise negation can be
done by a single insn.

As a result, '((x < 0) ? ~x : x)' cannot be optimized to '(x ^ (x >> 31))'
ever before, for example.

This patch relaxes such limitation, by putting the insn expansion off till
the split pass.

gcc/ChangeLog:

	* config/xtensa/xtensa.md (one_cmplsi2):
	Rearrange as an insn_and_split pattern.

gcc/testsuite/ChangeLog:

	* gcc.target/xtensa/one_cmpl_abs.c: New.
---
  gcc/config/xtensa/xtensa.md                   | 26 +++++++++++++------
  .../gcc.target/xtensa/one_cmpl_abs.c          |  9 +++++++
  2 files changed, 27 insertions(+), 8 deletions(-)
  create mode 100644 gcc/testsuite/gcc.target/xtensa/one_cmpl_abs.c

diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md
index 217879bde15..f11ae4910f8 100644
--- a/gcc/config/xtensa/xtensa.md
+++ b/gcc/config/xtensa/xtensa.md
@@ -556,16 +556,26 @@
     (set_attr "mode"	"SI")
     (set_attr "length"	"3")])

-(define_expand "one_cmplsi2"
-  [(set (match_operand:SI 0 "register_operand" "")
-	(not:SI (match_operand:SI 1 "register_operand" "")))]
+(define_insn_and_split "one_cmplsi2"
+  [(set (match_operand:SI 0 "register_operand" "=a")
+	(not:SI (match_operand:SI 1 "register_operand" "r")))]
    ""
+  "#"
+  "&& can_create_pseudo_p ()"
+  [(set (match_dup 2)
+	(const_int -1))
+   (set (match_dup 0)
+	(xor:SI (match_dup 1)
+		(match_dup 2)))]
  {
-  rtx temp = gen_reg_rtx (SImode);
-  emit_insn (gen_movsi (temp, constm1_rtx));
-  emit_insn (gen_xorsi3 (operands[0], temp, operands[1]));
-  DONE;
-})
+  operands[2] = gen_reg_rtx (SImode);
+}
+  [(set_attr "type"	"arith")
+   (set_attr "mode"	"SI")
+   (set (attr "length")
+	(if_then_else (match_test "TARGET_DENSITY")
+		      (const_int 5)
+		      (const_int 6)))])

  (define_insn "negsf2"
    [(set (match_operand:SF 0 "register_operand" "=f")
diff --git a/gcc/testsuite/gcc.target/xtensa/one_cmpl_abs.c 
b/gcc/testsuite/gcc.target/xtensa/one_cmpl_abs.c
new file mode 100644
index 00000000000..608f65fd777
--- /dev/null
+++ b/gcc/testsuite/gcc.target/xtensa/one_cmpl_abs.c
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+/* { dg-options "-O1" } */
+
+int one_cmpl_abs(int a)
+{
+  return a < 0 ? ~a : a;
+}
+
+/* { dg-final { scan-assembler-not "bgez" } } */
-- 
2.20.1

Re: [PATCH 2/4] xtensa: Make one_cmplsi2 optimizer-friendly

[Max Filippov]

On Sun, May 29, 2022 at 4:00 AM Takayuki 'January June' Suwa
<jjsuwa_sys3175@yahoo.co.jp> wrote:
>
> In Xtensa ISA, there is no single machine instruction that calculates unary
> bitwise negation.  But a few optimizers assume that bitwise negation can be
> done by a single insn.
>
> As a result, '((x < 0) ? ~x : x)' cannot be optimized to '(x ^ (x >> 31))'
> ever before, for example.
>
> This patch relaxes such limitation, by putting the insn expansion off till
> the split pass.
>
> gcc/ChangeLog:
>
>         * config/xtensa/xtensa.md (one_cmplsi2):
>         Rearrange as an insn_and_split pattern.
>
> gcc/testsuite/ChangeLog:
>
>         * gcc.target/xtensa/one_cmpl_abs.c: New.
> ---
>   gcc/config/xtensa/xtensa.md                   | 26 +++++++++++++------
>   .../gcc.target/xtensa/one_cmpl_abs.c          |  9 +++++++
>   2 files changed, 27 insertions(+), 8 deletions(-)
>   create mode 100644 gcc/testsuite/gcc.target/xtensa/one_cmpl_abs.c

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

-- 
Thanks.
-- Max