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From: "syq at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/111376] missed optimization of one bit test on MIPS32r1
Date: Sat, 15 Jun 2024 07:18:42 +0000	[thread overview]
Message-ID: <bug-111376-4-bkLkPfI6bL@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-111376-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111376

--- Comment #14 from YunQiang Su <syq at gcc dot gnu.org> ---
And it seems that the performance of SLL is related with the operand.

Just iterate from 0 to 1e9:

```
0000000000000b00 <f32>:
 b00:   000223c0        sll     a0,v0,0xf     #### <-- the code is something
wrong
                                              #### in normal code, we should
access
                                              #### v0 here.  v0 will be 100 or
1000.
 b04:   04810003        bgez    a0,b14 <f32+0x14>
 b08:   00000000        nop
 b0c:   03e00008        jr      ra
 b10:   240203e8        li      v0,1000
 b14:   03e00008        jr      ra
 b18:   24020064        li      v0,100
 b1c:   00000000        nop
```

is slower than

```
0000000000000b00 <f32>:
 b00:   000223c0        sll     a0,a0,0xf
 b04:   04810003        bgez    a0,b14 <f32+0x14>
 b08:   00000000        nop
 b0c:   03e00008        jr      ra
 b10:   240203e8        li      v0,1000
 b14:   03e00008        jr      ra
 b18:   24020064        li      v0,100
 b1c:   00000000        nop
```


I have no idea how to make a trade off here.

  parent reply	other threads:[~2024-06-15  7:18 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-11 18:24 [Bug rtl-optimization/111376] New: " lis8215 at gmail dot com
2024-06-04  6:55 ` [Bug target/111376] " syq at gcc dot gnu.org
2024-06-04  7:00 ` syq at gcc dot gnu.org
2024-06-04  7:06 ` lis8215 at gmail dot com
2024-06-05 11:02 ` syq at gcc dot gnu.org
2024-06-05 16:56 ` syq at gcc dot gnu.org
2024-06-06  9:45 ` lis8215 at gmail dot com
2024-06-06 22:16 ` syq at gcc dot gnu.org
2024-06-07  8:25 ` lis8215 at gmail dot com
2024-06-13  4:50 ` syq at gcc dot gnu.org
2024-06-15  3:22 ` syq at gcc dot gnu.org
2024-06-15  3:24 ` syq at gcc dot gnu.org
2024-06-15  5:24 ` lis8215 at gmail dot com
2024-06-15  6:47 ` syq at gcc dot gnu.org
2024-06-15  7:18 ` syq at gcc dot gnu.org [this message]
2024-06-15  8:13 ` lis8215 at gmail dot com
2024-06-15  8:35 ` lis8215 at gmail dot com
2024-06-18  8:06 ` syq at gcc dot gnu.org
2024-06-19 14:18 ` syq at gcc dot gnu.org

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