Hotspot JVM C2 compiler does this optimization, with varying degree of success but generally brittle and completely opaque. It doesn't actually stack allocate

Hotspot JVM C2 compiler does this optimization, with varying degree of success but generally brittle and completely opaque. It doesn't actually stack allocate them technically speaking, just scalarizes them into registers. Should also mention that this requires sufficient inlining to take place at minimum (unfortunately, hotspot does not do flow sensitive analysis so any conditional logic that makes the object escape, even if not taken, will be regarded as escaping - graal handles this better), which doesn't always happen for a variety of reasons. But what does this have to do with heap being faster than stack? This is doing roughly the same thing as a compiler that supports explicit stack allocations.