* Re: next glibc showstopper
[not found] <9712012221.AA15274@vlsi1.ultra.nyu.edu>
@ 1997-12-03 5:46 ` Bernd Schmidt
1997-12-06 7:50 ` Jeffrey A Law
0 siblings, 1 reply; 4+ messages in thread
From: Bernd Schmidt @ 1997-12-03 5:46 UTC (permalink / raw)
To: Richard Kenner; +Cc: egcs
> This indeed should have been done in i386.[ch].
>
> Can you show me the exact RTL so we can figure out where it should
> be changed?
I've figured it out. It turned out to be caused by a piece of code from
Intel's pentium patches that shouldn't have gotten in there. Removing this
code fixes the problem.
Bernd
* i386.c (notice_update_cc): Remove bogus pentium GCC code.
*** ./config/i386/i386.c.orig-1 Tue Dec 2 20:08:51 1997
--- ./config/i386/i386.c Tue Dec 2 20:12:18 1997
*************** notice_update_cc (exp)
*** 3542,3556 ****
if (SET_DEST (exp) == pc_rtx)
return;
- #ifdef IS_STACK_MODE
- /* Moving into a memory of stack_mode may have been moved
- in between the use and set of cc0 by loop_spl(). So
- old value of cc.status must be retained */
- if (GET_CODE(SET_DEST(exp)) == MEM
- && IS_STACK_MODE (GET_MODE (SET_DEST (exp))))
- return;
- #endif
-
/* Moving register or memory into a register:
it doesn't alter the cc's, but it might invalidate
the RTX's which we remember the cc's came from.
--- 3542,3547 ----
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: next glibc showstopper
1997-12-03 5:46 ` next glibc showstopper Bernd Schmidt
@ 1997-12-06 7:50 ` Jeffrey A Law
0 siblings, 0 replies; 4+ messages in thread
From: Jeffrey A Law @ 1997-12-06 7:50 UTC (permalink / raw)
To: Bernd Schmidt; +Cc: Richard Kenner, egcs
In message <Pine.SOL.3.90.971203141551.10301F-100000@ohara.informatik.rwth-aa
chen.de>you write:
> > This indeed should have been done in i386.[ch].
> >
> > Can you show me the exact RTL so we can figure out where it should
> > be changed?
>
> I've figured it out. It turned out to be caused by a piece of code from
> Intel's pentium patches that shouldn't have gotten in there. Removing this
> code fixes the problem.
>
> Bernd
>
> * i386.c (notice_update_cc): Remove bogus pentium GCC code.
Thanks. I've installed this patch into egcs.
jeff
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: next glibc showstopper
1997-11-21 21:50 Ulrich Drepper
@ 1997-12-01 5:20 ` Bernd Schmidt
0 siblings, 0 replies; 4+ messages in thread
From: Bernd Schmidt @ 1997-12-01 5:20 UTC (permalink / raw)
To: Ulrich Drepper; +Cc: egcs, kenner
> Here's the next problem which prevent successfully compiling the glibc
> with the current egcs on ix86:
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> double r (double, double);
>
> extern inline int
> bar (double x)
> {
> union { double d; int i[2]; } u = { d: x }; return u.i[1] < 0;
> }
>
> int
> foo (double d1, double d2)
> {
> double e = r (d1, d2);
>
> if (bar (d1) && bar (e)) <---- PROBLEM
> return 1;
> else
> return 5;
>
> return 0;
> }
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> The fault part of the code is this:
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 12: e8 fc ff ff ff call 13 <foo+0x13>
> 17: dd 45 08 fldl 0x8(%ebp)
> 1a: dd 5d f8 fstpl 0xfffffff8(%ebp)
>
> if (bar (d1) && bar (e))
> 1d: 83 7d fc 00 cmpl $0x0,0xfffffffc(%ebp)
> 21: 7d 0d jnl 30 <foo+0x30>
> 23: dd 5d f8 fstpl 0xfffffff8(%ebp) \ here is something
> 26: 7d 0a jnl 32 <foo+0x32> / missing
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> After the call to `r' (address 12) the return value is in %st(0). The
> according to the inline function `d1' is tested. It is copied on the
> stack (why?) and the correct word is tested against $0. This is ok.
>
> But now the return value must be checked. Here only the storing
> happens but NO compare instruction sets the flags. I.e., the flags as
> determined for `d1' are used.
That's because GCC thinks the flags are still valid from the previous
compare instruction. The NOTICE_UPDATE_CC macro fails to clear the remembered
status after the second store.
I've attached a patch which tries to solve this problem in final.c. I noticed
that there's a lot of code in i386.c which implements NOTICE_UPDATE_CC, but
I think the code which deals with invalidating cc_status could be moved to
a machine-independent file. The patch doesn't attempt to do this in the best
possible way, it only fixes the bug.
Note: there's another place in final.c where NOTICE_UPDATE_CC is used. I'm
not sure whether that place should be updated as well.
Bernd
*** ./final.c.orig-1 Sat Nov 29 20:46:49 1997
--- ./final.c Sat Nov 29 20:34:11 1997
*************** final (first, file, optimize, prescan)
*** 1332,1337 ****
--- 1332,1351 ----
add_bb (file);
}
\f
+ #ifdef HAVE_cc0
+ /* Invalidate cc_status if remembered values are clobbered by an
+ insn. Called via note_stores. */
+ static void
+ invalidate_cc_status (dest, set)
+ rtx set;
+ rtx dest;
+ {
+ if ((cc_status.value1 && reg_overlap_mentioned_p (dest, cc_status.value1))
+ || (cc_status.value2 && reg_overlap_mentioned_p (dest, cc_status.value2)))
+ CC_STATUS_INIT;
+ }
+ #endif
+
/* The final scan for one insn, INSN.
Args are same as in `final', except that INSN
is the insn being scanned.
*************** final_scan_insn (insn, file, optimize, p
*** 2122,2131 ****
--- 2136,2148 ----
cc_prev_status = cc_status;
/* Update `cc_status' for this instruction.
+ First, forget values that this insn clobbers.
+
The instruction's output routine may change it further.
If the output routine for a jump insn needs to depend
on the cc status, it should look at cc_prev_status. */
+ note_stores (PATTERN (insn), invalidate_cc_status);
NOTICE_UPDATE_CC (body, insn);
#endif
^ permalink raw reply [flat|nested] 4+ messages in thread
* next glibc showstopper
@ 1997-11-21 21:50 Ulrich Drepper
1997-12-01 5:20 ` Bernd Schmidt
0 siblings, 1 reply; 4+ messages in thread
From: Ulrich Drepper @ 1997-11-21 21:50 UTC (permalink / raw)
To: egcs
Hi,
Here's the next problem which prevent successfully compiling the glibc
with the current egcs on ix86:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
double r (double, double);
extern inline int
bar (double x)
{
union { double d; int i[2]; } u = { d: x }; return u.i[1] < 0;
}
int
foo (double d1, double d2)
{
double e = r (d1, d2);
if (bar (d1) && bar (e)) <---- PROBLEM
return 1;
else
return 5;
return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The fault part of the code is this:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
12: e8 fc ff ff ff call 13 <foo+0x13>
17: dd 45 08 fldl 0x8(%ebp)
1a: dd 5d f8 fstpl 0xfffffff8(%ebp)
if (bar (d1) && bar (e))
1d: 83 7d fc 00 cmpl $0x0,0xfffffffc(%ebp)
21: 7d 0d jnl 30 <foo+0x30>
23: dd 5d f8 fstpl 0xfffffff8(%ebp) \ here is something
26: 7d 0a jnl 32 <foo+0x32> / missing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
After the call to `r' (address 12) the return value is in %st(0). The
according to the inline function `d1' is tested. It is copied on the
stack (why?) and the correct word is tested against $0. This is ok.
But now the return value must be checked. Here only the storing
happens but NO compare instruction sets the flags. I.e., the flags as
determined for `d1' are used.
-- Uli
---------------. drepper at gnu.org ,-. Rubensstrasse 5
Ulrich Drepper \ ,-------------------' \ 76149 Karlsruhe/Germany
Cygnus Solutions `--' drepper at cygnus.com `------------------------
^ permalink raw reply [flat|nested] 4+ messages in thread
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[not found] <9712012221.AA15274@vlsi1.ultra.nyu.edu>
1997-12-03 5:46 ` next glibc showstopper Bernd Schmidt
1997-12-06 7:50 ` Jeffrey A Law
1997-11-21 21:50 Ulrich Drepper
1997-12-01 5:20 ` Bernd Schmidt
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