Created attachment 124469 [details]
Histogram kernel backtrace

If I compile ImageMagick with OpenCL support, the current version segfaults
when I attempt to do any operation which computes a histogram. This is actually
done frequently internally, so it's more crippling than it first appears.

To reproduce:

1. Get the current latest ImageMagick from GitHub:
https://github.com/ImageMagick/ImageMagick

2. Compile it with OpenCL support (--enable-opencl flag)

3. Get an image, and try to equalize its colors (based on the histogram):

convert input.png -equalize output.png

4. The segfault will occur

LLVM version: r272184
Mesa version: commit d5491a8
ImageMagick version: ade0d8e

The source code for the Histogram kernel is in
MagickCore/accelerate-kernels-private.h, starting on line 1283.