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From: "phosit at autistici dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/19347] Invariant load not moved out of loop
Date: Wed, 03 Jan 2024 19:14:07 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 4.0.0
X-Bugzilla-Keywords: alias, missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: phosit at autistici dot org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D19347

Phosit <phosit at autistici dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |phosit at autistici dot org

--- Comment #9 from Phosit <phosit at autistici dot org> ---
When there are few iterations (likely when it is unroled) there is no
alias-check:

void fill(int* data, int& value)
{
    for(unsigned long i{0}; i !=3D 4; ++i)
        data[i] =3D value;
}

--- at -O2 results in:
fill(int*, int&):
        movd    xmm1, DWORD PTR [rsi]
        pshufd  xmm0, xmm1, 0xe0
        movq    QWORD PTR [rdi], xmm0
        movd    xmm0, DWORD PTR [rsi]
        pshufd  xmm0, xmm0, 0xe0
        movq    QWORD PTR [rdi+8], xmm0
        ret

---
At -O3 the loop isn't removed and (thus) there is an alias-check.=