re PR rtl-optimization/28634 (rounding problem with -fdelayed-branch on hppa/mips)

gcc/
	PR rtl-optimization/28634
	* reorg.c (fill_slots_from_thread): Do not assume A + X - X == A
	for floating-point modes unless flag_unsafe_math_optimizations.

gcc/testsuite/
	PR rtl-optimization/28634
	* gcc.c-torture/execute/ieee/pr28634.c: New test.

From-SVN: r116124

gcc/ChangeLog

+2006-08-14  Richard Sandiford  <richard@codesourcery.com>
+
+	PR rtl-optimization/28634
+	* reorg.c (fill_slots_from_thread): Do not assume A + X - X == A
+	for floating-point modes unless flag_unsafe_math_optimizations.
+
 2006-08-13  Alexandre Oliva  <aoliva@redhat.com>
 	    Andrew Pinski  <pinskia@physics.uc.edu>
 

gcc/reorg.c

@@ -2817,6 +2817,8 @@ fill_slots_from_thread (rtx insn, rtx condition, rtx thread,
       dest = SET_DEST (pat), src = SET_SRC (pat);
       if ((GET_CODE (src) == PLUS || GET_CODE (src) == MINUS)
 	  && rtx_equal_p (XEXP (src, 0), dest)
+	  && (!FLOAT_MODE_P (GET_MODE (src))
+	      || flag_unsafe_math_optimizations)
 	  && ! reg_overlap_mentioned_p (dest, XEXP (src, 1))
 	  && ! side_effects_p (pat))
 	{

gcc/testsuite/ChangeLog

+2006-08-14  Richard Sandiford  <richard@codesourcery.com>
+
+	PR rtl-optimization/28634
+	* gcc.c-torture/execute/ieee/pr28634.c: New test.
+
 2006-08-13  Alexandre Oliva  <aoliva@redhat.com>
 
 	PR c/27184

gcc/testsuite/gcc.c-torture/execute/ieee/pr28634.c

+/* PR rtl-optimization/28634.  On targets with delayed branches,
+   dbr_schedule could do the next iteration's addition in the
+   branch delay slot, then subtract the value again if the branch
+   wasn't taken.  This can lead to rounding errors.  */
+double x = -0x1.0p53;
+double y = 1;
+int
+main (void)
+{
+  while (y > 0)
+    y += x;
+  if (y != x + 1)
+    abort ();
+  exit (0);
+}