GCSE problem involving mem_first_set.

[Geoff Keating <geoffk at ozemail dot com dot au>]

The attached short program, "test14.c" (originally part of TeX),
abort()s when compiled and run on powerpc-unknown-linux-gnu with

gcc -O2 -msdata=sysv test14.c -o test14-exec && ./test14-exec

but not with lower optimisation levels or (annoyingly) without
-msdata=sysv.

The problem is in GCSE; in the variables mem_first_set and
mem_last_set, 0 is used as a flag value meaning 'never set' but 0 can
also be a valid CUID.  I fixed it by using -1 as the flag value; see
patch attached.

This should probably be in egcs 1.1.1 if it is ever released.

-- 
Geoffrey Keating <geoffk@ozemail.com.au>

===File ~/gcc-bugs/test14.c=================================
extern  long curcs  ; 
extern  long curtok  ; 

void gettoken();

void 
getrtoken ( ) 
{    
  lab20: do {
      gettoken () ; 
  } while ( ! ( curtok != 2592 ) ) ; 
  if ( ( curcs == 0 ) || ( curcs > 10014 ) ) 
  {
    goto lab20 ; 
  } 
} 

long curcs = 1;
long curtok = 2592;

void gettoken (void)
{
  if (curtok == 0)
    abort();
  curtok = 0;
}

int main(void)
{
  getrtoken();
}
============================================================

===File ~/patches/egcs-6.diff===============================
Mon Sep 14 22:08:04 1998  Geoff Keating  <geoffk@ozemail.com.au>

	* gcse.c: New definition NEVER_SET for reg_first_set, reg_last_set,
	mem_first_set, mem_last_set; because 0 can be a CUID.
	(oprs_unchanged_p): Use new definition.
	(record_last_reg_set_info): Likewise.
	(record_last_mem_set_info): Likewise.
	(compute_hash_table): Likewise.

--- gcc/gcse.c~	Sat Aug 15 10:32:17 1998
+++ gcc/gcse.c	Mon Sep 14 22:06:25 1998
@@ -1055,6 +1055,8 @@ compute_sets (f)
 
 /* Hash table support.  */
 
+#define NEVER_SET -1
+
 /* For each register, the cuid of the first/last insn in the block to set it,
    or zero if not set.  */
 static int *reg_first_set;
@@ -1130,22 +1132,22 @@ oprs_unchanged_p (x, insn, avail_p)
     {
     case REG:
       if (avail_p)
-	return (reg_last_set[REGNO (x)] == 0
+	return (reg_last_set[REGNO (x)] == NEVER_SET
 		|| reg_last_set[REGNO (x)] < INSN_CUID (insn));
       else
-	return (reg_first_set[REGNO (x)] == 0
+	return (reg_first_set[REGNO (x)] == NEVER_SET
 		|| reg_first_set[REGNO (x)] >= INSN_CUID (insn));
 
     case MEM:
       if (avail_p)
 	{
-	  if (mem_last_set != 0
+	  if (mem_last_set != NEVER_SET
 	      && mem_last_set >= INSN_CUID (insn))
 	    return 0;
 	}
       else
 	{
-	  if (mem_first_set != 0
+	  if (mem_first_set != NEVER_SET
 	      && mem_first_set < INSN_CUID (insn))
 	    return 0;
 	}
@@ -1959,7 +1961,7 @@ record_last_reg_set_info (insn, regno)
      rtx insn;
      int regno;
 {
-  if (reg_first_set[regno] == 0)
+  if (reg_first_set[regno] == NEVER_SET)
     reg_first_set[regno] = INSN_CUID (insn);
   reg_last_set[regno] = INSN_CUID (insn);
   SET_BIT (reg_set_in_block[BLOCK_NUM (insn)], regno);
@@ -1971,7 +1973,7 @@ static void
 record_last_mem_set_info (insn)
      rtx insn;
 {
-  if (mem_first_set == 0)
+  if (mem_first_set == NEVER_SET)
     mem_first_set = INSN_CUID (insn);
   mem_last_set = INSN_CUID (insn);
   mem_set_in_block[BLOCK_NUM (insn)] = 1;
@@ -2041,16 +2043,17 @@ compute_hash_table (f, set_p)
       rtx insn;
       int regno;
       int in_libcall_block;
+      int i;
 
       /* First pass over the instructions records information used to
 	 determine when registers and memory are first and last set.
 	 ??? The mem_set_in_block and hard-reg reg_set_in_block computation
 	 could be moved to compute_sets since they currently don't change.  */
 
-      bzero ((char *) reg_first_set, max_gcse_regno * sizeof (int));
-      bzero ((char *) reg_last_set, max_gcse_regno * sizeof (int));
-      mem_first_set = 0;
-      mem_last_set = 0;
+      for (i = 0; i < max_gcse_regno; i++)
+	reg_first_set[i] = reg_last_set[i] = NEVER_SET;
+      mem_first_set = NEVER_SET;
+      mem_last_set = NEVER_SET;
 
       for (insn = basic_block_head[bb];
 	   insn && insn != NEXT_INSN (basic_block_end[bb]);
============================================================