ppc-eabi execute/fp-cmp-1.c -O2 failure

[Joern Rennecke]

execute/fp-cmp-1.c fails on ppc-eabi when compiled with -O2 .  This happens
because jump does an optimization that is equivalent to reversing the
condition for a floating point test - one which cannot be properly reversed.
The patch below is a bit dated, but I have just checked that it applies
cleanly to ss-970912 and that it fixes the bug there - which is still present
in the unpatched ss-970912.

I think it should be safe because

- It just restricts the circumstances under which an option may be performed.
- the parameters passed to can_reverse_comparison_p have already been used
  to calculate code1.  Thus, they should be valid.

Tue Apr 29 22:45:51 1997  J"orn Rennecke <amylaar@cygnus.co.uk>

	* jump.c (thread_jumps): check can_reverse_comparison_p before
	threading a reversed-condition jump.

*** jump.c.97r1-orig	Fri Feb 28 06:34:33 1997
--- jump.c	Tue Apr 29 22:45:51 1997
*************** thread_jumps (f, max_reg, flag_before_lo
*** 4607,4613 ****
  	  if (rtx_equal_for_thread_p (b1op0, b2op0, b2)
  	      && rtx_equal_for_thread_p (b1op1, b2op1, b2)
  	      && (comparison_dominates_p (code1, code2)
! 		  || comparison_dominates_p (code1, reverse_condition (code2))))
  	    {
  	      t1 = prev_nonnote_insn (b1);
  	      t2 = prev_nonnote_insn (b2);
--- 4607,4616 ----
  	  if (rtx_equal_for_thread_p (b1op0, b2op0, b2)
  	      && rtx_equal_for_thread_p (b1op1, b2op1, b2)
  	      && (comparison_dominates_p (code1, code2)
! 		  || (comparison_dominates_p (code1, reverse_condition (code2))
! 		      && can_reverse_comparison_p (XEXP (SET_SRC (PATTERN (b1)),
! 							 0),
! 						   b1))))
  	    {
  	      t1 = prev_nonnote_insn (b1);
  	      t2 = prev_nonnote_insn (b2);