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* [Bug middle-end/108906] New: Bogus may be used uninitialized warning
@ 2023-02-23 17:32 burnus at gcc dot gnu.org
2023-02-24 12:52 ` [Bug tree-optimization/108906] " rguenth at gcc dot gnu.org
2023-02-25 10:56 ` cvs-commit at gcc dot gnu.org
0 siblings, 2 replies; 3+ messages in thread
From: burnus at gcc dot gnu.org @ 2023-02-23 17:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108906
Bug ID: 108906
Summary: Bogus may be used uninitialized warning
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
Target Milestone: ---
Split-off from on PR fortran/108621
This shows up with code generated by gfortran internally. The warning is bogus
and (rightly!) disappears when compiled with -Og, -Os, -O1 or higher:
Warning: ‘f.dim[idx.1_32].lbound’ may be used uninitialized
[-Wmaybe-uninitialized]
If I now look at the 021t.ssa dump, I see:
f.data = 0B;
...
_1 = f.data;
cfi.0.base_addr = _1;
...
_2 = cfi.0.base_addr;
if (_2 != 0B)
goto <bb 3>; [INV]
else
goto <bb 6>; [INV]
...
<bb 4> :
_3 = f.dim[idx.1_32].lbound;
...
<bb 6> :
fun (&cfi.0);
I get the same result when I use '_2 = f.data' instead, i.e. neither value
propagation works.
The basic block <bb 4> is the only place where idx.1_32 gets used - but as
f.data == NULL, we directly jump to <bb 6>. Seemingly, the range/value
propagation from 'f.data = 0' to '_2 = ' does not work.
* * *
Testcase – compile with "gfortran -Wall"; a variant is 'subroutine'
instead of 'program' but this does not have any effect, either.
program demo
use, intrinsic :: iso_c_binding, only : c_int
implicit none
interface
subroutine fun(f_p) bind(c)
import c_int
integer(c_int), pointer, intent(inout) :: f_p(:)
end subroutine
end interface
integer(c_int), pointer :: f(:)
nullify(f)
call fun(f)
end
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/108906] Bogus may be used uninitialized warning
2023-02-23 17:32 [Bug middle-end/108906] New: Bogus may be used uninitialized warning burnus at gcc dot gnu.org
@ 2023-02-24 12:52 ` rguenth at gcc dot gnu.org
2023-02-25 10:56 ` cvs-commit at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-02-24 12:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108906
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2023-02-24
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
We diagnose this from the early diagnostic pass where propagation is limited.
At some cost we could improve things here.
^ permalink raw reply [flat|nested] 3+ messages in thread
* [Bug tree-optimization/108906] Bogus may be used uninitialized warning
2023-02-23 17:32 [Bug middle-end/108906] New: Bogus may be used uninitialized warning burnus at gcc dot gnu.org
2023-02-24 12:52 ` [Bug tree-optimization/108906] " rguenth at gcc dot gnu.org
@ 2023-02-25 10:56 ` cvs-commit at gcc dot gnu.org
1 sibling, 0 replies; 3+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-02-25 10:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108906
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tobias Burnus <burnus@gcc.gnu.org>:
https://gcc.gnu.org/g:d3e427f684b0cd7cedbe7b93a06f455e562c5901
commit r13-6341-gd3e427f684b0cd7cedbe7b93a06f455e562c5901
Author: Tobias Burnus <tobias@codesourcery.com>
Date: Sat Feb 25 11:55:08 2023 +0100
Fortran: Skip bound conv in gfc_conv_gfc_desc_to_cfi_desc with intent(out)
ptr [PR108621]
When the dummy argument of the bind(C) proc is 'pointer, intent(out)', the
conversion
of the GFC to the CFI bounds can be skipped: it is not needed and avoids
issues with
noninit memory.
Note that the 'cfi->base_addr = gfc->addr' assignment is kept as the C code
of a user
might assume that a nullified pointer arrives as NULL (or even a specific
value).
For instance, gfortran.dg/c-interop/section-{1,2}.f90 assumes the value
NULL.
Note 2: The PR is about a may-be-uninitialized warning with intent(out). In
the PR's
testcase, the pointer was nullified and should not have produced that
warning.
That is a diagnostic issue, now tracked as PR middle-end/108906 as the
issue in principle
still exists (e.g. with 'intent(inout)'). [But no longer for intent(out).]
Note 3: With undefined pointers and no 'intent', accessing uninit memory is
unavoidable
on the caller side as the compiler cannot know what the C function does
(but this usage
determines whether the pointer is permitted be undefined or whether the
bounds must be
gfc-to-cfi converted).
gcc/fortran/ChangeLog:
PR fortran/108621
* trans-expr.cc (gfc_conv_gfc_desc_to_cfi_desc): Skip setting of
bounds of CFI desc for 'pointer,intent(out)'.
gcc/testsuite/ChangeLog:
PR fortran/108621
* gfortran.dg/c-interop/fc-descriptor-pr108621.f90: New test.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-02-23 17:32 [Bug middle-end/108906] New: Bogus may be used uninitialized warning burnus at gcc dot gnu.org
2023-02-24 12:52 ` [Bug tree-optimization/108906] " rguenth at gcc dot gnu.org
2023-02-25 10:56 ` cvs-commit at gcc dot gnu.org
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