https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
This seems to work.
--- gcc/config/i386/i386.md.jj 2018-05-02 23:55:44.000000000 +0200
+++ gcc/config/i386/i386.md 2018-05-07 22:27:18.848705146 +0200
@@ -19285,6 +19285,40 @@
const0_rtx);
})
+;; Likewise for cmpelim optimized pattern.
+(define_peephole2
+ [(set (match_operand:SWI 0 "register_operand")
+ (match_operand:SWI 1 "memory_operand"))
+ (parallel [(set (reg FLAGS_REG)
+ (compare (match_operator:SWI 3 "plusminuslogic_operator"
+ [(match_dup 0)
+ (match_operand:SWI 2 "<nonmemory_operand>")])
+ (const_int 0)))
+ (set (match_dup 0) (match_dup 3))])
+ (set (match_dup 1) (match_dup 0))]
+ "(TARGET_READ_MODIFY_WRITE || optimize_insn_for_size_p ())
+ && peep2_reg_dead_p (3, operands[0])
+ && !reg_overlap_mentioned_p (operands[0], operands[1])
+ && !reg_overlap_mentioned_p (operands[0], operands[2])
+ && (<MODE>mode != QImode
+ || immediate_operand (operands[2], QImode)
+ || any_QIreg_operand (operands[2], QImode))
+ && ix86_match_ccmode (peep2_next_insn (1),
+ (GET_CODE (operands[3]) == PLUS
+ || GET_CODE (operands[3]) == MINUS)
+ ? CCGOCmode : CCNOmode)"
+ [(parallel [(set (match_dup 4) (match_dup 6))
+ (set (match_dup 1) (match_dup 5))])]
+{
+ operands[4] = SET_DEST (XVECEXP (PATTERN (peep2_next_insn (1)), 0, 0));
+ operands[5]
+ = gen_rtx_fmt_ee (GET_CODE (operands[3]), GET_MODE (operands[3]),
+ copy_rtx (operands[1]), operands[2]);
+ operands[6]
+ = gen_rtx_COMPARE (GET_MODE (operands[4]), copy_rtx (operands[5]),
+ const0_rtx);
+})
+
;; Likewise for instances where we have a lea pattern.
(define_peephole2
[(set (match_operand:SWI 0 "register_operand")
