PHP How to set the preg-groups to "non-capture" (?:...)

In HTML page, I remove HTML comments like this

$contentHTML = preg_replace("#(?=<!--)([\s\S]*?)-->#", "", $contentHTML);

But on a huge page for preg_replace, I got "PHP Fatal error: Allowed memory size ..."

Perhaps, one solution, would use the non-matching group to avoid capturing text? Could someone explain how use on-matching group ?:

Or how can I suppress HTML comments in huge page without preg_replace?

Solution

Just unroll the regex as

$contentHTML = preg_replace("#<!--[^-]*(?:-(?!->)[^-]*)*-->#", "", $contentHTML);

See the regex demo. Comapre with yours taking about 3 times as more steps as mine with a very short example.

Details:

<!-- - start of comment
[^-]* - 0+ non--
(?:-(?!->)[^-]*)* - 0+ sequences of - that is not followed with -> and then 0+ non--s
--> - comment end