https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69827
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- cygwin probably runs into the target hooks querying libc functionality switch (gimple_call_combined_fn (stmt)) { CASE_CFN_COS: CASE_CFN_SIN: CASE_CFN_CEXPI: /* Make sure we have either sincos or cexp. */ if (!targetm.libc_has_function (function_c99_math_complex) && !targetm.libc_has_function (function_sincos)) break; arg = gimple_call_arg (stmt, 0); if (TREE_CODE (arg) == SSA_NAME) cfg_changed |= execute_cse_sincos_1 (arg);