[Bug c++/111159] New: [13 Regression] False positive -Wdangling-reference

[daniel at constexpr dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59

Bug ID: 59
   Summary: [13 Regression] False positive -Wdangling-reference
   Product: gcc
   Version: 13.2.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: daniel at constexpr dot org
  Target Milestone: ---

GCC 13.2.0 as well as git from today report a false positive
-Wdangling-reference warning for the following C++ code:

struct A {
int * i;
int & b() { return *i; }
};

int g = 42;

A a() {
return A{ &g };
}

int main() {
const int & i = a().b();
return i;
}

[Bug tree-optimization/107129] New: [13 Regression] False positive -Wstringop-overflow warning with -O2 or -O3

[daniel at constexpr dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107129

Bug ID: 107129
   Summary: [13 Regression] False positive -Wstringop-overflow
warning with -O2 or -O3
   Product: gcc
   Version: 13.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: tree-optimization
  Assignee: unassigned at gcc dot gnu.org
  Reporter: daniel at constexpr dot org
  Target Milestone: ---

Created attachment 53652
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53652&action=edit
Reduced testcase

The attached testcase produces the following warning with GCC 13.0.0 20221002
(commit 3290dcf):

$ /opt/gcc-dev/bin/c++ -O2 -c test.cpp 
test.cpp: In member function ‘void C::f()’:
test.cpp:39:33: warning: writing 1 byte into a region of size 0
[-Wstringop-overflow=]
   39 | c[i] = e(1.f - i, i);
  |~^~~~
test.cpp:9:23: note: at offset 1 into destination object ‘C4::r’ of size 1
9 | unsigned char r;
  |

[Bug tree-optimization/97953] [9/10 Regression] ICE (segfault) during GIMPLE pass: loopdone compiling libgcc/config/libbid/bid128_fma.c:190:1

[daniel at constexpr dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97953

--- Comment #29 from Daniel Scharrer  ---
Hi, shouldn't this be

 Known to fail  10.3.**1**
 Known to work  10.3.**2**

[Bug tree-optimization/103986] New: Miscompilation with -O2 -funswitch-loops and __builtin_unreachable in ternary operator

[daniel at constexpr dot org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103986

Bug ID: 103986
   Summary: Miscompilation with -O2 -funswitch-loops and
__builtin_unreachable in ternary operator
   Product: gcc
   Version: 10.3.1
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: tree-optimization
  Assignee: unassigned at gcc dot gnu.org
  Reporter: daniel at constexpr dot org
  Target Milestone: ---

Created attachment 52166
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52166&action=edit
Reduced test case

The loop in the attached reduced test case does not terminate when compiled
with -O3 or -O2 -funswitch-loops with GCC 9.4.0 or GCC 10.3.1 even though it
should only iterate 144 times.

Curiously, the programs works as expected when using an if() instead of the
ternary operator in the assume macro but maybe that's just luck.

I could not reproduce the issue with GCC 8.5.0, GCC 11.2.1 or my GCC 12
checkout from 20220102.