VAR|TMP overhaul

[iluuu1994]

The aim of this PR is twofold:

• Reduce the number of highly similar TMP|VAR handlers
• Avoid ZVAL_DEREF in most of these cases

This is achieved by guaranteeing that all zend_compile_expr() calls, as well as all other compile calls with BP_VAR_R, will result in a TMP variable. This implies that the result will not contain an IS_INDIRECT or IS_REFERENCE value, which was mostly already the case, with two exceptions:

• Calls to return-by-reference functions. Because return-by-reference functions are quite rare, this is solved by delegating the DEREF to the RETURN_BY_REF handler, which will examine the stack to check whether the caller expects a VAR or TMP to understand whether the DEREF is needed.

• By-reference assignments, including both $a = &$b, as well as [&$a] = $b. When the result of these expressions is used in a BP_VAR_R context, it will be passed to a new ZEND_DEREF opcode beforehand. This is exceptionally rare.

Preliminary testing shows a 1.1% wall time improvement in Symfony Demo and roughly 0.5% in Wordpress. Edit: Sadly I can now only measure a 0.15% improvement for Symfony, but 0.8% for Wordpress. Zend/bench.php improves by ~3% in my tests. There seems to be quite a bit of volatility involved, potentially in relation to binary layout. Regardless, I think this is unlikely to cause true slowdowns for code that doesn't use return-by-ref.

TODOs:

• Verify this doesn't break important optimizations
• Use zend_unwrap_reference(). I missed this function, I was looking for a macro.
• Check why JIT i-count regresses. Edit: Wordpress now reduces jitted code by 0.35%, Wordpress by 0.02%.
• Try to replace DEREF with QM_ASSIGN.

[github-actions]

AWS x86_64 (c7i.24xl)

Attribute	Value
Environment	aws
Runner	host
Instance type	c7i.metal-24xl (dedicated)
Architecture	x86_64
CPU	48 cores
CPU settings	disabled deeper C-states, disabled turbo boost, disabled hyper-threading
RAM	188 GB
Kernel	6.1.158-178.288.amzn2023.x86_64
OS	Amazon Linux 2023.9.20251117
GCC	14.2.1
Time	2025-12-02 23:39:44 UTC

Laravel 12.2.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@64d8	0.45975	0.46849	0.00110	0.23%	0.46671	0.00%	0.46677	0.00%	-4.600	0.999	44.29 MB
PHP - vm-early-deref	0.46401	0.46634	0.00045	0.10%	0.46518	-0.33%	0.46514	-0.35%	0.387	0.000	44.20 MB

Symfony 2.7.0 demo app - 100 consecutive runs, 50 warmups, 100 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@64d8	0.74017	0.74572	0.00125	0.17%	0.74186	0.00%	0.74164	0.00%	1.222	0.999	40.49 MB
PHP - vm-early-deref	0.73742	0.74991	0.00167	0.23%	0.73960	-0.30%	0.73909	-0.34%	3.013	0.000	40.61 MB

Wordpress 6.2 main page - 100 consecutive runs, 20 warmups, 20 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@64d8	0.57431	0.58907	0.00131	0.23%	0.57939	0.00%	0.57927	0.00%	3.617	0.999	44.05 MB
PHP - vm-early-deref	0.58042	0.59071	0.00140	0.24%	0.58203	0.46%	0.58177	0.43%	4.732	0.000	44.04 MB

bench.php - 100 consecutive runs, 10 warmups, 2 requests (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@64d8	0.42478	0.43729	0.00296	0.69%	0.42832	0.00%	0.42732	0.00%	1.726	0.999	26.98 MB
PHP - vm-early-deref	0.42704	0.44168	0.00292	0.68%	0.43045	0.50%	0.42962	0.54%	1.945	0.000	26.85 MB

micro_bench.php - 50 consecutive runs, 5 warmups, 1 request (sec)

PHP	Min	Max	Std dev	Rel std dev %	Mean	Mean diff %	Median	Median diff %	Skew	P-value	Memory
PHP - baseline@64d8	1.29754	1.34894	0.00922	0.70%	1.31365	0.00%	1.31393	0.00%	0.946	0.997	21.23 MB
PHP - vm-early-deref	1.35848	1.38456	0.00620	0.45%	1.36862	4.18%	1.36759	4.08%	0.682	0.000	21.10 MB

[iluuu1994]

YIELD_FROM from generators can throw if the generator is closed, even for empty arrays. So this optimization may be unsound.