Re: alpha bootstrap failure wrt loop

[Richard Henderson <rth at cygnus dot com>]

On Fri, Jan 29, 1999 at 06:04:54PM -0800, Richard Henderson wrote:
> The loop at the end of validate_replace_rtx_1 is (still) being
> miscompiled on Alpha, leading to a segv while compiling libgcc.a.
> 
> The problem appears to be reading from an uninitialized stack slot:

This is caused by move_movables not preserving the luid invariant.
The uid_luid array is completely undependable at the beginning of
strength_reduce.

The answer is to have strength_reduce recalculate; this also 
affords the opportunity to remove some other local recalculations
and do it all at once later.

This solves the problem as seen on alpha in that one instance.
I cannot yet bootstrap, but do get farther.  The new problem 
is a segv in reload, which I will look into tomorrow.


r~


	* loop.c (strength_reduce): After biv identification, unconditionally
	recompute luids for the entire loop.

--- loop.c	Fri Jan 29 23:30:08 1999
+++ z	Fri Jan 29 23:18:22 1999
@@ -4055,12 +4054,7 @@
 		  if (loop_dump_stream)
 		    fprintf (loop_dump_stream, "move after insn %d\n",
 			     INSN_UID (dominator));
-		  /* Avoid problems with luids by actually moving the insn
-		     and adjusting all luids in the range.  */
 		  reorder_insns (giv_insn, giv_insn, dominator);
-		  for (p = dominator; INSN_UID (p) >= max_uid_for_loop; )
-		    p = PREV_INSN (p);
-		  compute_luids (giv_insn, after_giv, INSN_LUID (p));
 		  /* If the only purpose of the init insn is to initialize
 		     this giv, delete it.  */
 		  if (single_set (bl->init_insn)
@@ -4069,12 +4063,7 @@
 		}
 	      else if (! insn_first_p (bl2->biv->insn, bl->biv->insn))
 		{
-		  rtx p = PREV_INSN (giv_insn);
-		  while (INSN_UID (p) >= max_uid_for_loop)
-		    p = PREV_INSN (p);
 		  reorder_insns (giv_insn, giv_insn, bl2->biv->insn);
-		  compute_luids (after_giv, NEXT_INSN (giv_insn),
-				 INSN_LUID (p));
 		}
 	      /* Remove this biv from the chain.  */
 	      if (bl->next)
@@ -4093,6 +4082,9 @@
 	}
     }
 
+  /* Moveable movement and reorginations above did not preserve luids.  */
+  compute_luids (loop_start, loop_end, 0);
+
   /* If a biv is unconditionally incremented several times in a row, convert
      all but the last increment into a giv.  */