When compiliung compiling a ctor or dtor, we need to devirtualize the
virtual function calls so we always call the implementation of the
current class.
When `ArePotentiallyOverlappingStringLiterals`, added in
https://github.com/llvm/llvm-project/pull/109208, compares string
literals it drops the front of the string with the greatest offset from
its base pointer. The number of characters dropped is equal to the
difference between the two strings' offsets from their base pointers.
This would trigger an assert when the resulting offset is past the end
of the object. Not only are one-past-the-end pointers legal constructs,
the compiler should not crash even when faced with illegal constructs.
rdar://149865910
Instead of manually adding a note pointing to the relevant template
parameter to every relevant error, which is very easy to miss, this
patch adds a new instantiation context note, so that this can work using
RAII magic.
This fixes a bunch of places where these notes were missing, and is more
future-proof.
Some diagnostics are reworked to make better use of this note:
- Errors about missing template arguments now refer to the parameter
which is missing an argument.
- Template Template parameter mismatches now refer to template
parameters as parameters instead of arguments.
It's likely this will add the note to some diagnostics where the
parameter is not super relevant, but this can be reworked with time and
the decrease in maintenance burden makes up for it.
This bypasses the templight dumper for the new context entry, as the
tests are very hard to update.
This depends on #125453, which is needed to avoid losing the context
note for errors occuring during template argument deduction.
Make lifetime management more explicit. We're only using this for
CXXPseudoDestructorExprs for now but we need this to handle
std::construct_at/placement-new after destructor calls later anyway.
... between unrelated declarations or literals.
Leaving this small (I haven't run the whole test suite locally) to get
some feedback on the wording and implementation first.
The output of the sample in
https://github.com/llvm/llvm-project/issues/117409 is now:
```console
./array.cpp:57:6: warning: expression result unused [-Wunused-value]
57 | am - aj.af();
| ~~ ^ ~~~~~~~
./array.cpp:70:8: error: call to consteval function 'L::L<bx>' is not a constant expression
70 | q(0, [] {
| ^
./array.cpp:57:6: note: arithmetic on addresses of literals has unspecified value
57 | am - aj.af();
| ^
./array.cpp:62:5: note: in call to 'al(&""[0], {&""[0]})'
62 | al(bp.af(), k);
| ^~~~~~~~~~~~~~
./array.cpp:70:8: note: in call to 'L<bx>({})'
70 | q(0, [] {
| ^~~~
71 | struct bx {
| ~~~~~~~~~~~
72 | constexpr operator ab<g<l<decltype(""[0])>::e>::e>() { return t(""); }
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
73 | };
| ~~
74 | return bx();
| ~~~~~~~~~~~~
75 | }());
| ~~~
```
The output for
```c++
int a, b;
constexpr int n = &b - &a
```
is now:
```console
./array.cpp:80:15: error: constexpr variable 'n' must be initialized by a constant expression
80 | constexpr int n = &b - &a;
| ^ ~~~~~~~
./array.cpp:80:22: note: arithmetic involving '&b' and '&a' has unspecified value
80 | constexpr int n = &b - &a;
| ^
1 error generated.
```
Track the identity of each string literal object produced by evaluation
with a global version number. Accept comparisons between literals of the
same version, and between literals of different versions that cannot
possibly be placed in overlapping storage. Treat the remaining
comparisons as non-constant.
---------
Co-authored-by: Timm Baeder <tbaeder@redhat.com>
Co-authored-by: Aaron Ballman <aaron@aaronballman.com>
