https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102463
--- Comment #6 from Andrew Macleod <amacleod at redhat dot com> --- That trapping routine (relation_fold_and_or) is looking to see if there are any relationships between dependencies that can be exploited. ie c_2 = a_6 > b_7 c_3 = a_6 < b_7 c_4 = c_2 && c_3 if (c_4 != 0) when looking at c_2 and c_3, it notes that they both depend on the same 2 ssa-names, a_6, and a_7. It then queries whether there is a relationship between them when c_2 is [1,1] and c_3 is [1,1]. If so, it then tries to apply that relation to see if the stmt can never be true or not based on that raw relation. In this case, the 2 defining stmts are both PHI nodes, which happen to have the same 2 ssa_names in the dependency list, so it matches the pattern being looked for: # ntdef_6 = PHI <newdef_10(2), _bfd_elf_merge_symbol_h.0_1(3)> # tdef_7 = PHI <_bfd_elf_merge_symbol_h.0_1(2), newdef_10(3)> _5 = __tdef_7 & ntdef_6 both names depend on the value of newdef_10 and _bfd_elf_merge_symbol_h.0_1, so a check is being made for a relationship between op1 and op2 in those stmts. Whats missing is that we can only check for operand relationships in range-ops enabled stmts... The phi will never overtly give us a relation between the first and second operand, so no need to check.
