https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89029
Bug ID: 89029
Summary: __builtin_constant_p erroneously true
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: pdimov at gmail dot com
Target Milestone: ---
In the following code:
```
inline bool assert_static_check( bool ev )
{
return __builtin_constant_p( ev ) && !ev;
}
struct X1
{
int v1_;
};
inline bool operator==( X1 const& x1, X1 const& x2 )
{
return x1.v1_ == x2.v1_;
}
int compare( X1 s1, X1 s2 )
{
return assert_static_check( s1 == s2 );
}
struct X2
{
int v1_;
int v2_;
};
inline bool operator==( X2 const& x1, X2 const& x2 )
{
return x1.v1_ == x2.v1_ && x1.v2_ == x2.v2_;
}
int compare( X2 s1, X2 s2 )
{
return assert_static_check( s1 == s2 );
}
```
the generated code for the first compare function is, correctly,
```
compare(X1, X1):
xor eax, eax
ret
```
but for the second, it is
```
compare(X2, X2):
mov eax, 1
cmp edi, esi
je .L6
ret
.L6:
sar rdi, 32
sar rsi, 32
xor eax, eax
cmp edi, esi
setne al
ret
```
which is incorrect, as `s1 == s2` isn't a constant here.
(g++ -std=c++17 -O3, https://godbolt.org/z/nn0-4k)
(This is simplified from an attempt to create a statically-diagnosed assert
facility that would warn when the asserted expression is known to be false:
https://godbolt.org/z/i5SXSd. Would've been cool if it worked.)
