Comment # 8
on bug 83510
from Marek Olšák
(In reply to Christoph Haag from comment #7) > I think in the new "Lightroom Interior" the blackness glitch is visible in a > more interesting way: > https://www.youtube.com/watch?v=R9N-srsF_Fg I think I've tracked down what's causing the blackness in all Unreal Engine demos: Division by zero. There are several options to fix this: 1) Use V_RCP_LEGACY_F32 instead of V_RCP_F32 (not available on Tonga and later chips). 2) Emulate V_RCP_LEGACY_F32(x) using (x != 0 ? 1/x : 0). This can be done in Mesa or LLVM. For LLVM, a new intrinsic rcp.legacy needs to be added. 3) Disable lowering DIV_TO_MUL_RCP in glsl-to-tgsi and see what happens. Not sure if this will change anything, but at least LLVM doesn't need the lowering and we might need to do the same workaround for TGSI_OPCODE_DIV. I've implemented (2) in Mesa and it fixes the Lightroom Interior demo. I'm not sure if that's the best solution.
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