The pending patch I have from Richi fixes this. Even so, it's the
uninit code that's confused.
Sigh...every single change to the threading code shines the light on
some warning bug.
If you take the calls.ii file from the aarch64 bootstrap and break on
the warning, you can see that the uninitalized use is for
const_upper_3934 here:
<bb 102> [local count: 315357954]:
# const_upper_3934 = PHI <const_upper_3937(D)(101), _6707(293)>
if (_881 != 0)
goto <bb 103>; [50.00%]
else
goto <bb 106>; [50.00%]
<bb 103> [local count: 157678977]:
if (const_upper_3934 > _6699)
goto <bb 105>; [89.00%]
else
goto <bb 294>; [11.00%]
<bb 294> [local count: 17344687]:
<bb 104> [local count: 157678977]:
goto <bb 107>; [100.00%]
<bb 105> [local count: 140334290]:
stack_usage_map.481_3930 = stack_usage_map;
_6441 = const_upper_3934 - _6699;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
PROBLEMATIC READ HERE
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_4819 = stack_usage_map.481_3930 + _6699;
__builtin_memset (_4819, 1, _6441);
goto <bb 104>; [11.00%]
const_upper_3934 could be undefined if it comes from BB101
(const_upper_3937(D)), but it only gets read for _881 != 0, so it
shouldn't warn.
I suggest -Wmaybe-uninitialized be turned off for that file until the
warning is fixed.
And yes, the proposed patch will also cure this, but the underlying
problem in the warning is still there.
Aldy
On Wed, Oct 6, 2021 at 3:24 PM Andreas Schwab <sch...@linux-m68k.org> wrote:
>
> On Okt 05 2021, Aldy Hernandez via Gcc-patches wrote:
>
> > From 5abe65668f602d53b8f3dc515508dc4616beb048 Mon Sep 17 00:00:00 2001
> > From: Aldy Hernandez <al...@redhat.com>
> > Date: Tue, 5 Oct 2021 15:03:34 +0200
> > Subject: [PATCH] Loosen loop crossing restriction in threader.
> >
> > Crossing loops is generally discouraged from the threader, but we can
> > make an exception when we don't cross the latch or enter another loop,
> > since this is just an early exit out of the loop.
>
> This breaks bootstrap on aarch64 (in stage2):
>
> In function 'void mark_stack_region_used(poly_uint64, poly_uint64)',
> inlined from 'rtx_def* emit_library_call_value_1(int, rtx, rtx,
> libcall_type, machine_mode, int, rtx_mode_t*)' at ../../gcc/calls.c:4536:29:
> ../../gcc/calls.c:206:26: error: 'const_upper' may be used uninitialized in
> this function [-Werror=maybe-uninitialized]
> 206 | stack_usage_map[i] = 1;
> | ~~~~~~~~~~~~~~~~~~~^~~
> ../../gcc/calls.c: In function 'rtx_def* emit_library_call_value_1(int, rtx,
> rtx, libcall_type, machine_mode, int, rtx_mode_t*)':
> ../../gcc/calls.c:202:39: note: 'const_upper' was declared here
> 202 | unsigned HOST_WIDE_INT const_lower, const_upper;
> | ^~~~~~~~~~~
>
> Andreas.
>
> --
> Andreas Schwab, sch...@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
>
