Re: [FFmpeg-devel] [PATCH] configure: Remove dcbzl check for e500v1 and e500v2 architectures

[Michael Niedermayer <michael@niedermayer.cc>]

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On Mon, Sep 26, 2022 at 11:51:44AM +0100, Peter Krefting wrote:
> The DCBZL instruction is not available for the e500v1 and e500v2
> architectures, but may still be recognized by the toolchain, so we need to
> remove the test for it explicitly for these architectures.
> 
> References: PowerPC™ e500 Core Family Reference Manual (Freescale)
> 
> Found-by: Ståle Kristoffersen <staalebk@ifi.uio.no>
> Compare: Commit d5733936d857ce5c7d28c0bc9e89a2e2548f8895
> ---
>  configure | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> This was originally fixed by commit d5733936d857ce5c7d28c0bc9e89a2e2548f8895
> in version 2.2, but later broke in a merge which introduced a "disable dcbzl",
> forgot to check for it in the ppc branch.
> 
> diff --git a/configure b/configure
> index 7a62f0c248..5d01833f40 100755
> --- a/configure
> +++ b/configure
> @@ -6058,7 +6058,9 @@ elif enabled ppc; then
> 
>      enable local_aligned
> 
> -    check_inline_asm dcbzl     '"dcbzl 0, %0" :: "r"(0)'
> +    if enabled dcbzl; then
> +        check_inline_asm dcbzl    '"dcbzl 0, %0" :: "r"(0)'
> +    fi

something like this
disabled dcbzl || check_inline_asm dcbzl    '"dcbzl 0, %0" :: "r"(0)'

seems more clear
what this is supposed to do is to disable the instruction when it was
explicitly disabled for the target CPU

thx

{...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.

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