Fix GH-16996: 8.4 tracing JIT phpseclib failures

[dstogov]

This prevents conflicts caused by spilling to bound PHP stack slots by creating copies.

[ndossche]

I see, thanks for the fix. Sorry I didn't get to this earlier, I was at work.

I see we may be creating a potentially unused copy of a variable, and storing its ir reference in the register allocation table, if we don't end up binding to a slot after all. I suppose that this doesn't negatively impact codegen.

[dstogov]

I suppose that this doesn't negatively impact codegen.

This may make regression in some places and improvements in the others.
Actually, register allocator eliminates most of these copies using the same register for result and source.
I compared the code generated for bebch.php, Symfony, PHP-Patser and Wordpress and didn't see significant difference.

[ndossche]

Okay thanks