https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70873
--- Comment #18 from H.J. Lu <hjl.tools at gmail dot com> --- For float_truncate, (define_split [(set (match_operand:SF 0 "register_operand") (float_truncate:SF (match_operand:DF 1 "nonimmediate_operand")))] "TARGET_USE_VECTOR_FP_CONVERTS && optimize_insn_for_speed_p () && reload_completed && SSE_REG_P (operands[0]) && (!EXT_REX_SSE_REG_P (operands[0]) || TARGET_AVX512VL)" ;; It's more profitable to split and then extend in the same register. (define_peephole2 [(set (match_operand:SF 0 "register_operand") (float_truncate:SF (match_operand:DF 1 "memory_operand")))] "TARGET_SPLIT_MEM_OPND_FOR_FP_CONVERTS && optimize_insn_for_speed_p () && SSE_REG_P (operands[0])" [(set (match_dup 2) (match_dup 1)) (set (match_dup 0) (float_truncate:SF (match_dup 2)))] "operands[2] = gen_rtx_REG (DFmode, REGNO (operands[0]));")