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Re: subreg rtl documentation

From: Paolo Bonzini <bonzini at gnu dot org>
To: Ulrich Weigand <uweigand at de dot ibm dot com>
Cc: Kenneth Zadeck <zadeck at naturalbridge dot com>, Jeff Law <law at redhat dot com>, Weigand Ulrich <Ulrich dot Weigand at de dot ibm dot com>, Bernd Schmidt <bernds_cb1 at t-online dot de>, Jim Wilson <wilson at tuliptree dot org>, gcc-patches at gcc dot gnu dot org, Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>, "Joseph S. Myers" <joseph at codesourcery dot com>
Date: Sat, 12 Apr 2008 09:36:33 +0200
Subject: Re: subreg rtl documentation
References: <200804111926.m3BJQPxR011378@d12av02.megacenter.de.ibm.com>

(define_insn "clztidi2"
  [(set (match_operand:TI 0 "register_operand" "=d")
        (ior:TI
          (ashift:TI
            (zero_extend:TI
              (xor:DI (match_operand:DI 1 "register_operand" "d")
                      (lshiftrt (match_operand:DI 2 "const_int_operand" "")
                                (subreg:SI (clz:DI (match_dup 1)) 4))))

            (const_int 64))
          (zero_extend:TI (clz:DI (match_dup 1)))))
   (clobber (reg:CC CC_REGNUM))]

We don't allow (clz:SI (reg:DI X)), so this may well fall under "pattern recognized as combine".

I came to the conclusion that the only really bogus usage however is subregs of mems that are matched by register_operand. They are generated by combine because of LOAD_EXTEND_OP, and they ought to disappear; everything else can stay.

Paolo

Follow-Ups:
- son of subreg rtl documentation
  - From: Kenneth Zadeck

References:
- Re: subreg rtl documentation
  - From: Ulrich Weigand

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