Bug fix for consec_sets_giv

[Bernd Schmidt]

The function consec_sets_giv sets REG_IV_TYPE tentatively for the reg
it is examining.  It does not reset it before returning; however, if it
returns a benefit of zero, we will not call record_giv for this register.
This means we end up with a garbage value in REG_IV_INFO.  This showed up
as an infinite recursion when simplify_giv_expr tried to look up the
affected register.

Setting REG_IV_TYPE in this function can also clobber a previous value of
NOT_BASIC_INDUCT.  The patch avoids this as well.

I'm currently testing this with an sh-elf compiler and a bootstrap on x86.


Bernd

	* loop.c (consec_sets_giv): If the reg we're examining is anything
	but UNKNOWN_INDUCT, do nothing.
	Reset the reg's type to UNKNOWN_INDUCT before returning.

Index: loop.c
===================================================================
RCS file: /cvs/gcc/egcs/gcc/loop.c,v
retrieving revision 1.295
diff -u -p -r1.295 loop.c
--- loop.c	2000/11/13 22:20:02	1.295
+++ loop.c	2000/11/20 11:55:01
@@ -6203,8 +6203,12 @@ consec_sets_giv (loop, first_benefit, p,
      general_induction_var below, so we can allocate it on our stack.
      If this is a giv, our caller will replace the induct var entry with
      a new induction structure.  */
-  struct induction *v
-    = (struct induction *) alloca (sizeof (struct induction));
+  struct induction *v;
+
+  if (REG_IV_TYPE (ivs, REGNO (dest_reg)) != UNKNOWN_INDUCT)
+    return 0;
+
+  v = (struct induction *) alloca (sizeof (struct induction));
   v->src_reg = src_reg;
   v->mult_val = *mult_val;
   v->add_val = *add_val;
@@ -6265,6 +6269,7 @@ consec_sets_giv (loop, first_benefit, p,
 	}
     }
 
+  REG_IV_TYPE (ivs, REGNO (dest_reg)) = UNKNOWN_INDUCT;
   *last_consec_insn = p;
   return v->benefit;
 }