[FFmpeg-devel] [PATCH] Revert "lavu/timer: remove gratuitous volatile"

[FFmpeg-devel] [PATCH] Revert "lavu/timer: remove gratuitous volatile"

[Rémi Denis-Courmont]

It does not make much sense to me, but GCC somehow optimises the
inline assembler way even when the output are very obviously used.

This reverts commit 09731fbfc3a914ec4f6ffad60aa9062db6a8f6aa.
---
 libavutil/riscv/timer.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavutil/riscv/timer.h b/libavutil/riscv/timer.h
index df1a730b5e..174b469cbe 100644
--- a/libavutil/riscv/timer.h
+++ b/libavutil/riscv/timer.h
@@ -29,13 +29,13 @@ static inline uint64_t ff_read_time(void)
 #if (__riscv_xlen >= 64)
     uintptr_t cycles;
 
-    __asm__ ("rdtime  %0" : "=r" (cycles));
+    __asm__ volatile ("rdtime  %0" : "=r" (cycles));
 
 #else
     uint64_t cycles;
     uint32_t hi, lo, check;
 
-    __asm__ (
+    __asm__ volatile (
         "1: rdtimeh %0\n"
         "   rdtime  %1\n"
         "   rdtimeh %2\n"
-- 
2.40.1

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Re: [FFmpeg-devel] [PATCH] Revert "lavu/timer: remove gratuitous volatile"

[Martin Storsjö]

On Wed, 27 Sep 2023, Rémi Denis-Courmont wrote:

> It does not make much sense to me, but GCC somehow optimises the
> inline assembler way even when the output are very obviously used.
>
> This reverts commit 09731fbfc3a914ec4f6ffad60aa9062db6a8f6aa.
> ---
> libavutil/riscv/timer.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/libavutil/riscv/timer.h b/libavutil/riscv/timer.h
> index df1a730b5e..174b469cbe 100644
> --- a/libavutil/riscv/timer.h
> +++ b/libavutil/riscv/timer.h
> @@ -29,13 +29,13 @@ static inline uint64_t ff_read_time(void)
> #if (__riscv_xlen >= 64)
>     uintptr_t cycles;
>
> -    __asm__ ("rdtime  %0" : "=r" (cycles));
> +    __asm__ volatile ("rdtime  %0" : "=r" (cycles));
>
> #else
>     uint64_t cycles;
>     uint32_t hi, lo, check;
>
> -    __asm__ (
> +    __asm__ volatile (
>         "1: rdtimeh %0\n"
>         "   rdtime  %1\n"
>         "   rdtimeh %2\n"
> -- 
> 2.40.1

LGTM

// Martin
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