Files to reproduce problem

glsl_reduced.frag is a minimized GLSL shader. When compiled to SPIR-V with glslangValidator we get glsl_reduced.spv. I tried to further reduce this using spirv-reduce, but it failed due to a spirv-reduce bug, which I will report separately.

Doing:

spirv-opt glsl_reduced.spv --convert-local-access-chains --eliminate-local-singl
e-store --eliminate-local-single-store --eliminate-dead-code-aggressive --copy-p
ropagate-arrays --inline-entry-points-exhaustive --if-conversion --eliminate-loc
al-single-store --scalar-replacement=100 --inline-entry-points-exhaustive --priv
ate-to-local --ccp --eliminate-dead-branches --private-to-local --vector-dce --s
calar-replacement=100 --merge-blocks --eliminate-dead-branches --eliminate-dead-
branches --merge-return --scalar-replacement=100 --simplify-instructions --merge
-blocks --private-to-local --inline-entry-points-exhaustive --eliminate-local-si
ngle-block -o temp.spv

spirv-val temp.spv

should trigger the problem:

error: line 77: The continue construct with the continue target 46[%46] is not p
ost dominated by the back-edge block 58[%58]
%58 = OpLabel

I did not try to reduce the spirv-opt flags, in case (as with #2450) there may be an issue both with the optimizer generating invalid code and the validator not picking this up soon enough.

Found using GraphicsFuzz