peephole2: dead regs not marked as dead

[Paolo Bonzini]

On 10/29/2010 06:18 PM, Georg Lay wrote:
> (define_split
>    [(set (match_operand:SI 0 "register_operand"           "")
>          (and:SI (match_operand:SI 1 "register_operand"   "")
>                  (match_operand:SI 2 "const_int_operand"  "")))
>     (clobber (match_operand:SI 3 "register_operand" ""))]
>    "..."
>    [(set (match_dup 3)
>          (and:SI (match_dup 1)
>                  (match_dup 4)))
>     (set (match_dup 0)
>          (xor:SI (match_dup 3)
>                  (match_dup 1)))]

Again, it's not really my field but I think this should be written as

(define_split
    [(set (match_operand:SI 0 "register_operand"           "")
          (and:SI (match_operand:SI 1 "register_operand"   "")
                  (match_operand:SI 2 "const_int_operand"  "")))
     (clobber (match_scratch:SI 3 ""))]
    ""
    [(set (match_dup 3)
          (and:SI (match_dup 1)
                  (match_dup 4)))
     (set (match_dup 0)
          (xor:SI (match_dup 3)
                  (match_dup 1)))]

and the define_insn should also use match_scratch.  I'm looking at 
config/i386/i386.md, pattern fix_trunc<mode>_i387_fisttp_with_temp and 
the two following splits.

If you do it pre-reload, register allocation should not have any problem 
allocating operands 0 and 3 to the same register.  It sounds to me like 
you're doing your own register allocation using peepholes. :)

Paolo