Re: [PATCH] ASoC: soc-pcm: Shrink stack frame for __soc_pcm_hw_params

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 8/23/23 11:19, Mark Brown wrote:
> On Wed, Aug 23, 2023 at 03:49:58PM +0000, Charles Keepax wrote:
>> On Wed, Aug 23, 2023 at 10:21:13AM +0100, Charles Keepax wrote:
>>> Commit ac950278b087 ("ASoC: add N cpus to M codecs dai link support")
>>> added an additional local params in __soc_pmc_hw_params, for the
>>> CPU side of the DAI. The snd_pcm_hw_params struct is pretty large (604
>>> bytes) and keeping two local copies of it makes the stack frame for
>>> __soc_pcm_hw_params really large. As the two copies are only used
>>> sequentially combine these into a single local variable to shrink the
>>> stack frame.
> 
>> Hmm... this might need a little more thought its not clear why this
>> should change the frame size and it only seems to change the frame
>> size on the ARM cross compiler I am using, not x86.
> 
> Isn't that just going to be a function of the compiler being smart
> enough to work out that there aren't overlapping uses of the two
> variables and they can share stack space?  There's no reason not to help
> it figure that out.

One would think that compilers understand the variable scope, and
free-up the stack when leaving a for loop scope?