[Bug rtl-optimization/102842] [10 Regression] ICE in cselib_record_set at -O2 or greater

[vmakarov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102842

--- Comment #12 from Vladimir Makarov <vmakarov at gcc dot gnu.org> ---
The patch just hid the bug.  I believe the bug is still present on the trunk
too.

The insn in question is

(insn 26 64 109 3 (parallel [
            (set (reg:SI 134 [ _12 ])
                (plus:SI (mult:SI (reg:SI 117 [ _8 ])
                        (reg:SI 128))
                    (reg:SI 138)))
            (set (reg:SI 135 [ _12+4 ])
                (plus:SI (truncate:SI (lshiftrt:DI (plus:DI (mult:DI
(zero_extend:DI (reg:SI 117 [ _8 ]))
                                    (zero_extend:DI (reg:SI 128)))
                                (zero_extend:DI (reg:SI 138)))
                            (const_int 32 [0x20])))
                    (reg:SI 138)))
        ]) "a.cpp":15:32 70 {umlal}
     (expr_list:REG_DEAD (reg:SI 138)
        (expr_list:REG_DEAD (reg:SI 128)
            (nil))))

And its definition is 

(define_insn "<US>mlal"
  [(set (match_operand:SI 0 "s_register_operand" "=r,&r")
        (plus:SI
         (mult:SI
          (match_operand:SI 4 "s_register_operand" "%r,r")
          (match_operand:SI 5 "s_register_operand" "r,r"))
         (match_operand:SI 1 "s_register_operand" "0,0")))
   (set (match_operand:SI 2 "s_register_operand" "=r,&r")
        (plus:SI
         (truncate:SI
          (lshiftrt:DI
           (plus:DI
            (mult:DI (SE:DI (match_dup 4)) (SE:DI (match_dup 5)))
            (zero_extend:DI (match_dup 1)))
           (const_int 32)))
         (match_operand:SI 3 "s_register_operand" "2,2")))]
  "TARGET_32BIT"
  "<US>mlal%?\\t%0, %2, %4, %5"
  [(set_attr "type" "umlal")
   (set_attr "predicable" "yes")
   (set_attr "arch" "v6,nov6")]

After couple of LRA constraints and assignment sub-passes, the two output
operands get the same hard reg.  And this results in cse abort in post-reload
pass.

The issue is that reload pseudos for pseudos 134 and 135 get the same value as
they both are matched with different occurrences of pseudo 138 in the insn.

The bug is in a very sensitive LRA code area and fixing it will take some time.
 But I hope I'll have a fix at the end of next week.