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From: "bina2374 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/94092] New: Code size and performance
 degradations after -ftree-loop-distribute-patterns was enabled at -O[2s]+
Date: Mon, 09 Mar 2020 06:06:25 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 10.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94092

            Bug ID: 94092
           Summary: Code size and performance degradations after
                    -ftree-loop-distribute-patterns was enabled at -O[2s]+
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bina2374 at gmail dot com
  Target Milestone: ---
            Target: riscv64-unknown-elf

Since https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D88440,
loop-distribute-patterns was enabled at -O[2s]+. We understand that this pa=
tch
is helpful in some cases, but not for all.
In the original bugzilla, the loop count is known, and the performance and =
code
size are all improved finally. However, if loop count is unknown, the resul=
ts
may become worse.

void init_array(int N, int *array) {
  int i;
  for (i =3D 0; i < N; i++)
    array[i] =3D 0;
}

init_array:
        mv      a2,a0
        mv      a0,a1
        ble     a2,zero,.L1
        slli    a2,a2,2
        li      a1,0
        tail    memset
.L1:
        ret

For coremark, this is not only harmful to performance, but also code size.
Therefore, I suggest that we have to discuss how to resolve the case of unk=
nown
loop count.=