I've got this bug too.
I've bisected and found that most shaders packs starts to hang at commit
7e414b58640aee6e243d337e72cea290c354f632
"glsl: break the gl_FragData array into separate gl_FragData[i] variables"
However, one of them starts to hang with an earlier commit:
edbbfac6cfc634e697d7f981155a5072c52d77ac
"r600g: fast color clears for single-sample buffers"

This only happens on evergreen+ hardware(tested on JUNIPER and THAMES, works
fine on RV770).

A workaround is to set the environment variable R600_DEBUG=notiling.

This bug also happens in various Unreal Engine 4 demos. (tested on Reflections
Subway Demo, where the hang happens at the beginning). The environment variable
also solves the problem.