From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jim Wilson <wilson@cygnus.com>
To: Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
Cc: amylaar@cygnus.com, egcs@cygnus.com
Subject: Re: Missing documentation in regmove.c 
Date: Mon, 11 May 1998 18:12:00 -0000
Message-id: <199805120112.SAA26199@rtl.cygnus.com>
References: <vyzvhrd6v0q.fsf@issan.informatik.uni-dortmund.de>
X-SW-Source: 1998-05/msg00391.html

I added some comments which should help.

Index: regmove.c
===================================================================
RCS file: /egcs/carton/cvsfiles/egcs/gcc/regmove.c,v
retrieving revision 1.16
diff -p -r1.16 regmove.c
*** regmove.c	1998/04/18 15:42:46	1.16
--- regmove.c	1998/05/12 01:09:17
*************** reg_is_remote_constant_p (reg, insn, fir
*** 568,575 ****
--- 568,591 ----
    return 0;
  }
  
+ /* INSN is adding a CONST_INT to a REG.  We search backwards looking for
+    another add immediate instruction with the same source and dest registers,
+    and if we find one, we change INSN to an increment, and return 1.  If
+    no changes are made, we return 0.
+ 
+    This changes
+      (set (reg100) (plus reg1 offset1))
+      ...
+      (set (reg100) (plus reg1 offset2))
+    to
+      (set (reg100) (plus reg1 offset1))
+      ...
+      (set (reg100) (plus reg100 offset2-offset1))  */
+ 
+ /* ??? What does this comment mean?  */
  /* cse disrupts preincrement / postdecrement squences when it finds a
     hard register as ultimate source, like the frame pointer.  */
+ 
  int
  fixup_match_2 (insn, dst, src, offset, regmove_dump_file)
       rtx insn, dst, src, offset;
*************** regmove_optimize (f, nregs, regmove_dump
*** 1141,1147 ****
--- 1157,1168 ----
  #endif /* REGISTER_CONSTRAINTS */
  }
  
+ /* Returns the INSN_CODE for INSN if its pattern has matching constraints for
+    any operand.  Returns -1 if INSN can't be recognized, or if the alternative
+    can't be determined.
  
+    Initialize the info in MATCHP based on the constraints.  */
+ 
  static int
  find_matches (insn, matchp)
       rtx insn;
*************** stable_but_for_p (x, src, dst)
*** 1708,1715 ****
        return ! rtx_unstable_p (x);
      }
  }
  
- /* Test if regmove seems profitable for this target.  */
  int
  regmove_profitable_p ()
  {
--- 1729,1739 ----
        return ! rtx_unstable_p (x);
      }
  }
+ 
+ /* Test if regmove seems profitable for this target.  Regmove is useful only
+    if some common patterns are two address, i.e. require matching constraints,
+    so we check that condition here.  */
  
  int
  regmove_profitable_p ()
  {