regmove.c (regmove_optimize): Suppress the optimization for unchanging destination register.

	* regmove.c (regmove_optimize): Suppress the optimization for
	unchanging destination register.  Add comment above function.

From-SVN: r41974

gcc/ChangeLog

+2001-05-11  Jakub Jelinek  <jakub@redhat.com>
+
+	* regmove.c (regmove_optimize): Suppress the optimization for
+	unchanging destination register.  Add comment above function.
+
 2001-05-11  Zack Weinberg  <zackw@stanford.edu>
 
 	* Makefile.in: Exterminate all references to assert.h.

gcc/regmove.c

@@ -1060,6 +1060,12 @@ fixup_match_2 (insn, dst, src, offset, regmove_dump_file)
   return 0;
 }
 
+/* Main entry for the register move optimization.
+   F is the first instruction.
+   NREGS is one plus the highest pseudo-reg number used in the instruction.
+   REGMOVE_DUMP_FILE is a stream for output of a trace of actions taken
+   (or 0 if none should be output).  */
+
 void
 regmove_optimize (f, nregs, regmove_dump_file)
      rtx f;
@@ -1282,7 +1288,8 @@ regmove_optimize (f, nregs, regmove_dump_file)
 
 	      if (GET_CODE (dst) != REG
 		  || REGNO (dst) < FIRST_PSEUDO_REGISTER
-		  || REG_LIVE_LENGTH (REGNO (dst)) < 0)
+		  || REG_LIVE_LENGTH (REGNO (dst)) < 0
+		  || RTX_UNCHANGING_P (dst))
 		continue;
 
 	      /* If the operands already match, then there is nothing to do. */