MergedAlloc encouraging errors (was buffer override effect when going from 64 samples to 256 samples in REAPER)

[p0nce]

User sent a video that illustrates the problem. Very probably not a Dplug problem (99% confidence) but how to avoid that kind of bug could be a documentation problem. EDIT: Lens had similar issue at release

[p0nce]

Reproduced, VST2 or VST3, in REAPER v6.82 + Windows with Steinberg UR22 ASIO driver.

To reproduce:

• set ASIO buffer to 256 in the ASIO panel
• instantiate Inner Pitch
• play clean sound
• set buffer size to 64 in the ASIO panel
• play sound, there is a regular buffer sound

[p0nce]

Reproduce with process:

$ process -i dance.wav "Inner Pitch 1.0.dll" -buffer 64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,64,512,512,512,512,512,512 -o output.wav

gives in the 64 to 256 transition:

[p0nce]

This was a buffer not resized from 64 to 128 samples, Intel Inspector find the bug approximately. What would help is a warning from MergedAlloc in debug mode, that sentinel bytes have changed. For example it could use malloc instead of one merged allocation.

The problem is that MergedAlloc and aligned allocation can hide more bugs, because no protection fault happen. Or, simply using slices instead of pointers work too.

[p0nce]

Added detection of most buffer overflows when using MergedAllocation. Each buffer has 32-byte of 0xCC after.