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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/42612] post-increment addressing not used
Date: Tue, 12 Jul 2022 05:39:59 +0000 [thread overview]
Message-ID: <bug-42612-4-sz3rXR8bw3@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-42612-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Dmitry Baksheev from comment #6)
> Please consider fixing this issue. Here is another example where not using
> post-increment for loops produces suboptimal code on AArch64. The code is 4x
> slower than LLVM-generated code for dot-product function:
>
> double dotprod(std::size_t n,
> const double* __restrict__ a,
> const double* __restrict__ b)
> {
> double ans = 0;
> #if __clang__
> #pragma clang loop vectorize(assume_safety)
> #else
> #pragma GCC ivdep
> #endif
> for (std::size_t i = 0; i < n; ++i) {
> ans += a[i] * b[i];
> }
> return ans;
> }
>
>
> Compile with: $(CXX) -march=armv8.2-a -O3 dp.cpp
>
> GCC-generated loop does not have post-increment loads:
> .L3:
>
> ldr d2, [x1, x3, lsl 3]
>
> ldr d1, [x2, x3, lsl 3]
>
> add x3, x3, 1
>
> fmadd d0, d2, d1, d0
>
> cmp x0, x3
>
> bne .L3
>
> Clang emits this:
> .LBB0_4:
> ldr d1, [x10], #8
>
> ldr d2, [x8], #8
>
> subs x9, x9, #1
> fmadd d0, d1, d2, d0
>
> b.ne .LBB0_4
I suspect that is a different issue. And I suspect it is a target cost issue
which depends on the core really. Because some cores the separate add is
better.
next prev parent reply other threads:[~2022-07-12 5:39 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-42612-4@http.gcc.gnu.org/bugzilla/>
2012-08-23 14:16 ` olegendo at gcc dot gnu.org
2015-05-22 13:57 ` olegendo at gcc dot gnu.org
2022-07-12 5:21 ` bd at mail dot ru
2022-07-12 5:39 ` pinskia at gcc dot gnu.org [this message]
2010-01-04 16:02 [Bug c/42612] New: [4.4/4.5] " jon at beniston dot com
2010-01-04 16:11 ` [Bug rtl-optimization/42612] " rguenth at gcc dot gnu dot org
2010-01-04 18:53 ` steven at gcc dot gnu dot org
2010-01-05 11:43 ` bonzini at gnu dot org
2010-01-05 12:13 ` jon at beniston dot com
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