* [PATCH 5/5] xtensa: Eliminate [DS]Cmode hard register clobber that is immediately followed by whole overwrite the register
@ 2022-06-14 3:53 Takayuki 'January June' Suwa
2022-06-16 0:02 ` Max Filippov
0 siblings, 1 reply; 2+ messages in thread
From: Takayuki 'January June' Suwa @ 2022-06-14 3:53 UTC (permalink / raw)
To: GCC Patches
RTL expansion of substitution to [DS]Cmode hard register includes obstructive
register clobber.
A simplest example:
double _Complex test(double _Complex c) {
return c;
}
will be converted to:
(set (reg:DF 42 [ c ]) (reg:DF 2 a2))
(set (reg:DF 43 [ c+8 ]) (reg:DF 4 a4))
(clobber (reg:DC 2 a2))
(set (reg:DF 2 a2) (reg:DF 42 [ c ]))
(set (reg:DF 4 a4) (reg:DF 43 [ c+8 ]))
(use (reg:DC 2 a2))
(return)
and then finally:
test:
mov a8, a2
mov a9, a3
mov a6, a4
mov a7, a5
mov a2, a8
mov a3, a9
mov a4, a6
mov a5, a7
ret
As you see, it is so ridiculous.
This patch eliminates such clobber in order to prune away the wasted move
instructions by the optimizer:
test:
ret
gcc/ChangeLog:
* config/xtensa/xtensa.md (DSC): New split pattern and mode iterator.
---
gcc/config/xtensa/xtensa.md | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/gcc/config/xtensa/xtensa.md b/gcc/config/xtensa/xtensa.md
index e6f5594762f..3b3be5f8436 100644
--- a/gcc/config/xtensa/xtensa.md
+++ b/gcc/config/xtensa/xtensa.md
@@ -86,6 +86,10 @@
;; This code iterator is for *shlrd and its variants.
(define_code_iterator ior_op [ior plus])
+;; This mode iterator allows the DC and SC patterns to be defined from
+;; the same template.
+(define_mode_iterator DSC [DC SC])
+
\f
;; Attributes.
@@ -2755,3 +2759,27 @@
operands[6] = gen_rtx_MEM (SFmode, XEXP (operands[6], 0));
operands[7] = gen_rtx_MEM (SFmode, XEXP (operands[7], 0));
})
+
+(define_split
+ [(clobber (match_operand:DSC 0 "register_operand"))]
+ "GP_REG_P (REGNO (operands[0]))"
+ [(const_int 0)]
+{
+ unsigned int regno = REGNO (operands[0]);
+ machine_mode inner_mode = GET_MODE_INNER (<MODE>mode);
+ rtx_insn *insn;
+ rtx x;
+ if (! ((insn = next_nonnote_nondebug_insn (curr_insn))
+ && NONJUMP_INSN_P (insn)
+ && GET_CODE (x = PATTERN (insn)) == SET
+ && REG_P (x = XEXP (x, 0))
+ && GET_MODE (x) == inner_mode
+ && REGNO (x) == regno
+ && (insn = next_nonnote_nondebug_insn (insn))
+ && NONJUMP_INSN_P (insn)
+ && GET_CODE (x = PATTERN (insn)) == SET
+ && REG_P (x = XEXP (x, 0))
+ && GET_MODE (x) == inner_mode
+ && REGNO (x) == regno + REG_NREGS (operands[0]) / 2))
+ FAIL;
+})
--
2.20.1
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH 5/5] xtensa: Eliminate [DS]Cmode hard register clobber that is immediately followed by whole overwrite the register
2022-06-14 3:53 [PATCH 5/5] xtensa: Eliminate [DS]Cmode hard register clobber that is immediately followed by whole overwrite the register Takayuki 'January June' Suwa
@ 2022-06-16 0:02 ` Max Filippov
0 siblings, 0 replies; 2+ messages in thread
From: Max Filippov @ 2022-06-16 0:02 UTC (permalink / raw)
To: Takayuki 'January June' Suwa; +Cc: GCC Patches
On Mon, Jun 13, 2022 at 8:54 PM Takayuki 'January June' Suwa
<jjsuwa_sys3175@yahoo.co.jp> wrote:
>
> RTL expansion of substitution to [DS]Cmode hard register includes obstructive
> register clobber.
>
> A simplest example:
>
> double _Complex test(double _Complex c) {
> return c;
> }
>
> will be converted to:
>
> (set (reg:DF 42 [ c ]) (reg:DF 2 a2))
> (set (reg:DF 43 [ c+8 ]) (reg:DF 4 a4))
> (clobber (reg:DC 2 a2))
> (set (reg:DF 2 a2) (reg:DF 42 [ c ]))
> (set (reg:DF 4 a4) (reg:DF 43 [ c+8 ]))
> (use (reg:DC 2 a2))
> (return)
>
> and then finally:
>
> test:
> mov a8, a2
> mov a9, a3
> mov a6, a4
> mov a7, a5
> mov a2, a8
> mov a3, a9
> mov a4, a6
> mov a5, a7
> ret
>
> As you see, it is so ridiculous.
>
> This patch eliminates such clobber in order to prune away the wasted move
> instructions by the optimizer:
>
> test:
> ret
>
> gcc/ChangeLog:
>
> * config/xtensa/xtensa.md (DSC): New split pattern and mode iterator.
> ---
> gcc/config/xtensa/xtensa.md | 28 ++++++++++++++++++++++++++++
> 1 file changed, 28 insertions(+)
Regtested for target=xtensa-linux-uclibc, no new regressions.
Committed to master.
--
Thanks.
-- Max
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2022-06-14 3:53 [PATCH 5/5] xtensa: Eliminate [DS]Cmode hard register clobber that is immediately followed by whole overwrite the register Takayuki 'January June' Suwa
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