Merged requested to merge cmarcelo/mesa:r/nir-deref-path-skip-trivial-casts into master
In a NIR generated using SPIR-V initializers to variables, copy propagation can end up transforming
vec1 32 ssa_33 = deref_var &@1 (shared mat2x4) vec1 32 ssa_35 = mov ssa_33 vec1 32 ssa_7 = deref_cast (mat2x4 *)ssa_35 (shared mat2x4) /* ptr_stride=0 */
vec1 32 ssa_33 = deref_var &@1 (shared mat2x4) vec1 32 ssa_7 = deref_cast (mat2x4 *)ssa_33 (shared mat2x4) /* ptr_stride=0 */
Before the optimization, the "head" of a path of deref that uses ssa_7 will be the cast. After, it will be the variable in ssa_33. Since the types are the same, this is a trivial cast that would be picked up by nir_opt_deref.
If we need to compare such deref-chain after optimization with another deref-chain for the same variable, the compare function will get confused by the cast in the middle.
One alternative would be to add nir_opt_deref to places that compare derefs, but that might not scale well, so skip the trivial casts when generating the paths instead.
Motivated by the discussion in !3047 (comment 383660).