Re: Loop optimization bug with Ada front end on PPC (and probably Alpha)

[Richard Henderson <rth@redhat.com>]

The problem is not limited to doloop -- the unroller ought
to hit this problem as well.  I'm testing the following.



r~



Index: loop.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/loop.c,v
retrieving revision 1.369
diff -c -p -d -r1.369 loop.c
*** loop.c	2001/11/15 23:44:56	1.369
--- loop.c	2001/11/26 01:52:34
*************** typedef struct loop_replace_args
*** 282,293 ****
    rtx insn;
  } loop_replace_args;
  
- /* Nonzero iff INSN is between START and END, inclusive.  */
- #define INSN_IN_RANGE_P(INSN, START, END)	\
-   (INSN_UID (INSN) < max_uid_for_loop		\
-    && INSN_LUID (INSN) >= INSN_LUID (START)	\
-    && INSN_LUID (INSN) <= INSN_LUID (END))
- 
  /* Indirect_jump_in_function is computed once per function.  */
  static int indirect_jump_in_function;
  static int indirect_jump_in_function_p PARAMS ((rtx));
--- 282,287 ----
Index: loop.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/loop.h,v
retrieving revision 1.56
diff -c -p -d -r1.56 loop.h
*** loop.h	2001/10/29 22:13:40	1.56
--- loop.h	2001/11/26 01:52:34
*************** Software Foundation, 59 Temple Place - S
*** 50,55 ****
--- 50,60 ----
  #define REGNO_FIRST_LUID(REGNO) uid_luid[REGNO_FIRST_UID (REGNO)]
  #define REGNO_LAST_LUID(REGNO) uid_luid[REGNO_LAST_UID (REGNO)]
  
+ /* Nonzero iff INSN is between START and END, inclusive.  */
+ #define INSN_IN_RANGE_P(INSN, START, END)	\
+   (INSN_UID (INSN) < max_uid_for_loop		\
+    && INSN_LUID (INSN) >= INSN_LUID (START)	\
+    && INSN_LUID (INSN) <= INSN_LUID (END))
  
  /* A "basic induction variable" or biv is a pseudo reg that is set
     (within this loop) only by incrementing or decrementing it.  */
Index: unroll.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/unroll.c,v
retrieving revision 1.147
diff -c -p -d -r1.147 unroll.c
*** unroll.c	2001/11/21 00:50:56	1.147
--- unroll.c	2001/11/26 01:52:34
*************** loop_iterations (loop)
*** 3480,3485 ****
--- 3480,3486 ----
    int unsigned_p, compare_dir, final_larger;
    rtx last_loop_insn;
    rtx reg_term;
+   rtx insn;
    struct iv_class *bl;
  
    loop_info->n_iterations = 0;
*************** loop_iterations (loop)
*** 3705,3710 ****
--- 3706,3762 ----
  
    if (initial_value == 0)
      return 0;
+ 
+   /* Some code transformations can result in code akin to
+ 
+ 	LOOP_BEG
+ 	  goto start;
+ 	top:
+ 	  i++;
+ 	start:
+ 	  ...
+ 	LOOP_CONT
+ 	  if (i < n) goto top;
+ 	LOOP_END
+ 
+      In this situation, we skip the increment the first time through
+      the loop, which results in an incorrect estimate of the number
+      of iterations.  As we did for GIVs above, adjust the initial value
+      to compensate.  */
+ 
+   off_by_one = 0;
+   for (insn = loop->start; insn != loop->top; insn = NEXT_INSN (insn))
+     if (GET_CODE (insn) == JUMP_INSN)
+       {
+ 	if (any_uncondjump_p (insn)
+ 	    && JUMP_LABEL (insn)
+ 	    && INSN_IN_RANGE_P (JUMP_LABEL (insn), loop->top, loop->cont))
+ 	  {
+ 	    if (reg_set_between_p (bl->biv->src_reg, insn, JUMP_LABEL (insn)))
+ 	      off_by_one = 1;
+ 	    break;
+ 	  }
+ 	/* No idea what's going on.  */
+ 	if (loop_dump_stream)
+ 	  fprintf (loop_dump_stream,
+ 		   "Loop iterations: Confused by jump before loop top.\n");
+ 	return 0;
+       }
+ 
+   if (off_by_one)
+     {
+       if (loop_dump_stream)
+ 	fprintf (loop_dump_stream,
+ 		 "Loop iterations: Basic induction var skips initial incr.\n");
+       if (GET_CODE (increment) != CONST_INT)
+ 	{
+ 	  if (loop_dump_stream)
+ 	    fprintf (loop_dump_stream,
+ 		     "Loop iterations: Can't adjust with non-constant incr.\n");
+ 	  return 0;
+ 	}
+       initial_value = plus_constant (initial_value, -INTVAL (increment));
+     }
  
    unsigned_p = 0;
    off_by_one = 0;