Public bug reported:
May be I made a mistake in the code, but the situation looks like a bug.
The problem belongs to gcc-7 and gcc-8.
Local variable E is created. The constructor successfully fills the
field E.t2.number with the value of -1.0.
After calling of an empty function with a const reference to tuple, the
value of E.t2.number is overwritten unexpectedly. The attached code
stores the value of E.t2.number before calling and after calling of an
empty function and then prints both.
The following line is printed with the preprocessed code attached:
v_before=-1.000000, v_after=0.000000
Compilation under Release configuration in Eclipse CDT generates another code.
In this situation the variable E.t2.number is not initialized properly. In this
case the following result is printed:
v_before=0.000000, v_after=0.000000
Unfortunately, I failed to create such preprocessed code. If I use -E option
and links the prerocessed code with g++-8, the value is initialized with -1.0
successfully and it corrupts only after the calling of an empty function.
The suspicious code:
...
void func(const std::tuple<int>& t)
{
}
int main()
{
...
auto E=A(I,J)-B(J,I);
double v_before=E.t2.number;
func(std::tuple<int>(1));
double v_after=E.t2.number;
printf("v_before=%lf, v_after=%lf\n",v_before, v_after);
}
** Affects: gcc-7 (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1835536
Title:
Stack-located variable is overwritten unexpectedly
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