[llvm] [AMDGPU] Fix uniform fcopysign pattern (PR #218644)

[Jay Foad via llvm-commits]

jayfoad wrote:

> In the end, the real calculation instruction `%33:vgpr_16 = nofpexcept V_ADD_F16_t16_e64...` will be marked dead.

I really can't understand why that would happen, based on the MIR that you showed. It sounds like there must be something wrong in the detect-dead-lanes pass?

https://github.com/llvm/llvm-project/pull/218644