abort in eliminate_regs compiling glob.c from glibc

[John David Anglin]

> > Breakpoint 2, eliminate_regs_in_insn (insn=0x406a0ba0, replace=0)
> >     at ../../gcc/reload1.c:2826
> > 2826      if (! insn_is_asm && icode < 0)
> > (gdb) p debug_rtx (insn)
> > (insn/s 2711 2709 2719 (set (reg:SI 6 %r6)
> >         (reg:SI 28 %r28)) 69 {pre_ldw-4} (insn_list 2708 (insn_list:REG_DEP_ANTI 2696 (insn_list:REG_DEP_ANTI 2702 (insn_list:REG_DEP_ANTI 2697 (nil)))))
> >     (expr_list:REG_DEAD (reg:SI 28 %r28)
> >         (insn_list:REG_RETVAL 2708 (expr_list:REG_EQUAL (expr_list (use (mem:BLK (scratch) 0))
> >                     (expr_list (symbol_ref/v:SI ("@strlen"))
> >                         (expr_list (reg/v:SI 4 %r4)
> >                             (nil))))
> >                 (nil)))))
> 
> The `use' arises from the `__pure__' attribute in the prototype for strlen:
> 
> extern size_t strlen (__const char *__s) __attribute__ ((__pure__));

Here is a patch to fix the abort in eliminate_regs when it encounters a USE.
As I understand the situation, there are three conditions needed to trigger
it:

1)	A function that contains insns with an eliminable register.
2)	The function must call __builtin_alloca to change the frame size
	from its initial size.
3)	After the call to __builtin_alloca, there must be a call to a
	pure function.

With the enclosed patch, I can now build glibc for hppa-linux with -O3
optimisation.

Please review carefully because I will be the first to admit that I don't
understand why the use is there in the first place and all the details of
what eliminate_reg does.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)

2000-11-14  John David Anglin  <dave@hiauly1.hia.nrc.ca>

	* reload1.c (eliminate_regs): Don't abort on MEM USEs.

--- reload1.c.orig	Wed Sep 27 14:27:23 2000
+++ reload1.c	Tue Nov 14 16:01:56 2000
@@ -2499,6 +2499,10 @@
 	return x;
 
     case USE:
+      /* Handle insn_list USE that a call to a pure functions may generate. */
+      new = eliminate_regs (XEXP (x, 0), 0, insn);
+      if (GET_CODE (new) == MEM)
+	return XEXP (new, 0);
     case CLOBBER:
     case ASM_OPERANDS:
     case SET: