Fix PR30957

From-SVN: r124471

gcc/ChangeLog

@@ -1,3 +1,9 @@
+2007-06-05  Revital Eres  <eres@il.ibm.com>
+
+	PR 30957
+	* loop-unroll.c (insert_var_expansion_initialization):
+	Initialize the expansions with -zero instead of +zero.
+
 2007-05-05  Aurelien Jarno  <aurelien@aurel32.net>
 
 	* config/pa/pa.md: Split tgd_load, tld_load and tie_load

gcc/loop-unroll.c

@@ -2014,7 +2014,30 @@ expand_var_during_unrolling (struct var_to_expand *ve, rtx insn)
 /* Initialize the variable expansions in loop preheader.  
    Callbacks for htab_traverse.  PLACE_P is the loop-preheader 
    basic block where the initialization of the expansions 
-   should take place.  */
+   should take place.  The expansions are initialized with (-0)
+   when the operation is plus or minus to honor sign zero.
+   This way we can prevent cases where the sign of the final result is
+   effected by the sign of the expansion.
+   Here is an example to demonstrate this:
+   
+   for (i = 0 ; i < n; i++)
+     sum += something;
+
+   ==>
+
+   sum += something
+   ....
+   i = i+1;
+   sum1 += something
+   ....
+   i = i+1
+   sum2 += something;
+   ....
+   
+   When SUM is initialized with -zero and SOMETHING is also -zero; the
+   final result of sum should be -zero thus the expansions sum1 and sum2
+   should be initialized with -zero as well (otherwise we will get +zero
+   as the final result).  */
 
 static int
 insert_var_expansion_initialization (void **slot, void *place_p)
@@ -2023,7 +2046,9 @@ insert_var_expansion_initialization (void **slot, void *place_p)
   basic_block place = (basic_block)place_p;
   rtx seq, var, zero_init, insn;
   unsigned i;
-  
+  enum machine_mode mode = GET_MODE (ve->reg);
+  bool honor_signed_zero_p = HONOR_SIGNED_ZEROS (mode);
+
   if (VEC_length (rtx, ve->var_expansions) == 0)
     return 1;
   
@@ -2031,7 +2056,11 @@ insert_var_expansion_initialization (void **slot, void *place_p)
   if (ve->op == PLUS || ve->op == MINUS) 
     for (i = 0; VEC_iterate (rtx, ve->var_expansions, i, var); i++)
       {
-        zero_init =  CONST0_RTX (GET_MODE (var));
+	if (honor_signed_zero_p)
+	  zero_init = simplify_gen_unary (NEG, mode, CONST0_RTX (mode), mode);
+	else
+	  zero_init = CONST0_RTX (mode);
+       	
         emit_move_insn (var, zero_init);
       }
   else if (ve->op == MULT)

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2007-06-05  Revital Eres  <eres@il.ibm.com>
+	
+	PR 30957
+	* gcc.dg/pr30957-1.c: New test.
+
 2007-05-05  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
 
 	PR fortran/31251

gcc/testsuite/gcc.dg/pr30957-1.c

@@ -0,0 +1,30 @@
+/* { dg-do run { xfail vax-*-* powerpc-*-*spe } } */
+/* { dg-options "-O2 -funroll-loops -funsafe-math-optimizations -fvariable-expansion-in-unroller -dL" } */
+
+extern void abort (void);
+extern void exit (int);
+
+float
+foo (float d, int n)
+{
+  unsigned i;
+  float accum = d;
+
+  for (i = 0; i < n; i++)
+    accum += d;
+
+  return accum;
+}
+
+int
+main ()
+{
+  if (__builtin_copysignf (1.0, foo (0.0 / -5.0, 10)) != -1.0)
+    abort ();
+  exit (0);
+}
+
+/* { dg-final { scan-rtl-dump "Expanding Accumulator" "loop2_unroll" } } */
+/* { dg-final { cleanup-rtl-dump "loop*" } } */
+
+