Re: Better fix for fix_truncsfdi2 i386 bug in egcs 1.1.2

[Jim Kingdon <kingdon at redhat dot com>]

> So, presumably the output is being written before scratch memory
> locations are used?

Yes.

> It would have helped if you indicated what path through
> output_fix_trunc and output_to_reg was used -- I had to spend a lot
> of time reading that code to see how we might be losing.

Thanks for suggesting this - it isn't that I forgot to mention this,
it is that I didn't know the compiler well enough to easily understand
how output_fix_trunc related to the other pieces and so on.  I think
I'm slowly gaining enlightenment.

> output_move_double knows how to handle cases where the destination overlaps
> with the inputs, so there's no possibility of losing in that code.

Right.  The egcs 1.1.2 equivalent (output_to_reg) doesn't handle those
cases, but it is a moot point in light of:

>   return AS1 (fldc%W2,%2);
> Hmmm.  I think this could cause a problem if the address for operands[2] used
> the same register as the output operand (operands[0]).
> Do you concur?

Yes, I concur (after stepping through the code on my test case and
thinking about it and so on).  Once I look at it right, it looks like
a straightforward application of the rule "Therefore, this
[earlyclobber] operand may not lie in a register that is used as
. . . part of any memory address" from md.texi.

> Can you please fix all the patterns which call output_fix_trunc such
> that they have an earlyclobber on the "!r" output alternative if you
> agree with my comments?

Patch enclosed.  Thanks for your patience/help - and I'm glad you took
the time because I wouldn't have noticed the SImode case without your
suggestions.

Tue Aug 24 15:54:32 1999  Jim Kingdon  <http://developer.redhat.com>
	with much help from Jeffrey A Law and Richard Henderson

	* config/i386/i386.md: In the 6 insns which call output_fix_trunc,
	operands[0] needs to be an earlyclobber if it is a register (since
	output_fix_trunc may access memory after setting operands[0]).

Index: config/i386/i386.md
===================================================================
RCS file: /cvs/egcs/egcs/gcc/config/i386/i386.md,v
retrieving revision 1.78
diff -c -r1.78 i386.md
*** i386.md	1999/04/25 11:43:46	1.78
--- i386.md	1999/08/24 20:02:45
***************
*** 2711,2717 ****
  }")
  
  (define_insn ""
!   [(set (match_operand:SI 0 "nonimmediate_operand" "=m,!r")
  	(fix:SI (fix:SF (match_operand:SF 1 "register_operand" "f,f"))))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
     (clobber (match_operand:HI 3 "memory_operand" "m,m"))
--- 2711,2717 ----
  }")
  
  (define_insn ""
!   [(set (match_operand:SI 0 "nonimmediate_operand" "=m,!&r")
  	(fix:SI (fix:SF (match_operand:SF 1 "register_operand" "f,f"))))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
     (clobber (match_operand:HI 3 "memory_operand" "m,m"))
***************
*** 2739,2745 ****
  }")
  
  (define_insn ""
!   [(set (match_operand:DI 0 "nonimmediate_operand" "=m,!r")
  	(fix:DI (fix:SF (match_operand:SF 1 "register_operand" "f,f"))))
     (clobber (match_dup 1))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
--- 2739,2745 ----
  }")
  
  (define_insn ""
!   [(set (match_operand:DI 0 "nonimmediate_operand" "=m,!&r")
  	(fix:DI (fix:SF (match_operand:SF 1 "register_operand" "f,f"))))
     (clobber (match_dup 1))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
***************
*** 2766,2772 ****
  }")
  
  (define_insn ""
!   [(set (match_operand:SI 0 "nonimmediate_operand" "=m,!r")
  	(fix:SI (fix:DF (match_operand:DF 1 "register_operand" "f,f"))))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
     (clobber (match_operand:HI 3 "memory_operand" "m,m"))
--- 2766,2772 ----
  }")
  
  (define_insn ""
!   [(set (match_operand:SI 0 "nonimmediate_operand" "=m,!&r")
  	(fix:SI (fix:DF (match_operand:DF 1 "register_operand" "f,f"))))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
     (clobber (match_operand:HI 3 "memory_operand" "m,m"))
***************
*** 2794,2800 ****
  }")
  
  (define_insn ""
!   [(set (match_operand:DI 0 "nonimmediate_operand" "=m,!r")
  	(fix:DI (fix:DF (match_operand:DF 1 "register_operand" "f,f"))))
     (clobber (match_dup 1))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
--- 2794,2800 ----
  }")
  
  (define_insn ""
!   [(set (match_operand:DI 0 "nonimmediate_operand" "=m,!&r")
  	(fix:DI (fix:DF (match_operand:DF 1 "register_operand" "f,f"))))
     (clobber (match_dup 1))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
***************
*** 2821,2827 ****
  }")
  
  (define_insn ""
!   [(set (match_operand:SI 0 "nonimmediate_operand" "=m,!r")
  	(fix:SI (fix:XF (match_operand:XF 1 "register_operand" "f,f"))))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
     (clobber (match_operand:HI 3 "memory_operand" "m,m"))
--- 2821,2827 ----
  }")
  
  (define_insn ""
!   [(set (match_operand:SI 0 "nonimmediate_operand" "=m,!&r")
  	(fix:SI (fix:XF (match_operand:XF 1 "register_operand" "f,f"))))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
     (clobber (match_operand:HI 3 "memory_operand" "m,m"))
***************
*** 2849,2855 ****
  }")
  
  (define_insn ""
!   [(set (match_operand:DI 0 "nonimmediate_operand" "=m,!r")
  	(fix:DI (fix:XF (match_operand:XF 1 "register_operand" "f,f"))))
     (clobber (match_dup 1))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))
--- 2849,2855 ----
  }")
  
  (define_insn ""
!   [(set (match_operand:DI 0 "nonimmediate_operand" "=m,!&r")
  	(fix:DI (fix:XF (match_operand:XF 1 "register_operand" "f,f"))))
     (clobber (match_dup 1))
     (clobber (match_operand:HI 2 "memory_operand" "m,m"))