[cfe-users] inconsistent compilation error inside constexpr if
Hello,
In the below code the compiler throws "undeclared identifier" when the
commented line is uncommented. Whereas the line just before compiles fine.
Regards,
Manu
typedef bool (* DummyFunc) ();
bool ExecDummy (DummyFunc fptr) {
if (fptr)
return fptr ();
return false;
}
constexpr unsigned int IsMyAppClient = 0;
constexpr bool CheckForTypeClient (unsigned int pAppType)
{
return ((pAppType & IsMyAppClient) != 0);
}
class MyAppTemplate
{
public:
template
staticboolMyAppInit ();
};
template
bool
MyAppTemplate::MyAppInit ()
{
if constexpr (CheckForTypeClient(T)) {
return ClientMain ();// no error
//return ExecDummy(ClientMain);// error: use of undeclared
identifier 'ClientMain'
}
return false;
}
int __cdecl
main (int pArgc, char* pArgv[])
{
constexpr int TVal = 3;
MyAppTemplate::MyAppInit ();
return 0;
}
___
cfe-users mailing list
cfe-users@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
Re: [cfe-users] inconsistent compilation error inside constexpr if
Hi David,
Thanks for the reply. I missed to mention the environment and what i am trying
to do.
1. Environment is ClangCL (version 10.0), Microsoft Visual Studio.
2. I assumed that since the 'constexpr if' evaluates to false, the
external function's presence would not be checked. So, if my application is not
of type 'client' ClientMain would not be called. My actual code inside the
constexpr if is the commented line of code that does not compile. To experiment
i simply invoked ClientMain directly which compiled fine.
Here is the assembly generated from the successful compilation (with the first
line inside 'constexpr if' enabled).
"??$MyAppInit@$02@MyAppTemplate@@SQ_NXZ": #
@"??$MyAppInit@$02@MyAppTemplate@@SQ_NXZ"
.Lfunc_begin2:
.cv_func_id 2
.cv_loc 2 1 32 0# Main.cpp:32:0
# %bb.0:
.cv_loc 2 1 39 0# Main.cpp:39:0
xor eax, eax
# kill: def $al killed $al killed $eax
.Ltmp6:
ret
.Ltmp7:
.Lfunc_end2:
Here is how the compiler is invoked:
E:\LLVM\bin\clang-cl.exe /c /Z7 /nologo /W3 /WX- /diagnostics:column /Od /D
_DEBUG /D _CONSOLE /D _UNICODE /D UNICODE /EHsc /MTd /GS /fp:precise
/permissive- /std:c++17 /FA /Fa"x64\Debug\\" /Fo"x64\Debug\\" /Gv /TP -m64
Main.cpp
1> Done executing task "CL".
Is my understanding of 'constexpr if' wrong ? won't the body get discarded in
case it gets evaluated to false?
Regards,
Manu
From: David Blaikie
Sent: Saturday, August 22, 2020 2:14 AM
To: Manu agarwal
Cc: cfe-users@lists.llvm.org
Subject: Re: [cfe-users] inconsistent compilation error inside constexpr if
>From what I could test on godbolt, using LLVM evrsions back to 5.0,
Clang does reject the "return ClientMain();" call you aren't seeing an
error on. So I'm not sure what compiler/version/situation you're
running, but at least at first blush it doesn't look like clang.
On Fri, Aug 21, 2020 at 1:29 PM Manu agarwal via cfe-users
wrote:
>
> Hello,
>
> In the below code the compiler throws "undeclared identifier" when the
> commented line is uncommented. Whereas the line just before compiles fine.
>
> Regards,
> Manu
>
> typedef bool (* DummyFunc) ();
>
>
> bool ExecDummy (DummyFunc fptr) {
>
> if (fptr)
> return fptr ();
>
> return false;
> }
>
> constexpr unsigned int IsMyAppClient = 0;
>
> constexpr bool CheckForTypeClient (unsigned int pAppType)
> {
> return ((pAppType & IsMyAppClient) != 0);
> }
>
>
> class MyAppTemplate
> {
> public:
> template
> staticboolMyAppInit ();
> };
>
> template
> bool
> MyAppTemplate::MyAppInit ()
> {
> if constexpr (CheckForTypeClient(T)) {
>
> return ClientMain ();// no error
> //return ExecDummy(ClientMain);// error: use of
> undeclared identifier 'ClientMain'
> }
>
> return false;
> }
>
> int __cdecl
> main (int pArgc, char* pArgv[])
> {
> constexpr int TVal = 3;
>
> MyAppTemplate::MyAppInit ();
>
> return 0;
> }
>
>
> ___
> cfe-users mailing list
> cfe-users@lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
___
cfe-users mailing list
cfe-users@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
Re: [cfe-users] inconsistent compilation error inside constexpr if
Thanks Richard and David for your replies. That was helpful.
Regards,
Manu
From: Richard Smith
Sent: Sunday, August 23, 2020 11:56 PM
To: Manu agarwal
Cc: cfe-users@lists.llvm.org
Subject: Re: [cfe-users] inconsistent compilation error inside constexpr if
On Fri, 21 Aug 2020 at 13:29, Manu agarwal via cfe-users
mailto:cfe-users@lists.llvm.org>> wrote:
Hello,
In the below code the compiler throws "undeclared identifier" when the
commented line is uncommented. Whereas the line just before compiles fine.
Regards,
Manu
typedef bool (* DummyFunc) ();
bool ExecDummy (DummyFunc fptr) {
if (fptr)
return fptr ();
return false;
}
constexpr unsigned int IsMyAppClient = 0;
constexpr bool CheckForTypeClient (unsigned int pAppType)
{
return ((pAppType & IsMyAppClient) != 0);
}
class MyAppTemplate
{
public:
template
staticboolMyAppInit ();
};
template
bool
MyAppTemplate::MyAppInit ()
{
if constexpr (CheckForTypeClient(T)) {
return ClientMain ();// no error
//return ExecDummy(ClientMain);// error: use of undeclared
identifier 'ClientMain'
}
This code is invalid, as David Blaikie explains. However, in MSVC-compatible
mode (under -fms-compatibility, which is enabled by default for some
Windows-targeting modes), Clang attempts to to accept certain invalid code that
MSVC has historically accepted, including this case, where we allow the call to
ClientMain() to find declarations of a ClientMain function that appear after
the template definition. That recovery from invalid code is only done for
certain syntactic patterns, such as unqualified function calls -- so it applies
to ClientMain() but not to (ClientMain).
return false;
}
int __cdecl
main (int pArgc, char* pArgv[])
{
constexpr int TVal = 3;
MyAppTemplate::MyAppInit ();
return 0;
}
___
cfe-users mailing list
cfe-users@lists.llvm.org<mailto:cfe-users@lists.llvm.org>
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
___
cfe-users mailing list
cfe-users@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
[cfe-users] -Winvalid-noreturn warning
Hi,
We have the below code where this warning gets generated.
#include
[[noreturn]] inline void
abc () noexcept
{
std::terminate ();
}
using MyNoReturn = void (*) () noexcept;
//using MyNoReturn = std::add_pointer_t;// even this
declaration, instead of the above, gives the same warning
[[noreturn]]
inline void IDontReturn () noexcept
{
std::terminate ();
}
static MyNoReturn gvar {IDontReturn};
[[noreturn]]
inline void
CallIDontReturn () noexcept
{
gvar (); // here is where clang gives
warning: function declared 'noreturn' should not return [-Winvalid-noreturn]
}
We have the used the below command to compile:
clang++ -std=c++17 -Wall -o runusing usingst.cpp
gcc does not show this warning.
Please let us know how we can use 'using' clause to declare function pointer to
a function that does not return, so that this warning does not show up.
Regards,
Manu
___
cfe-users mailing list
cfe-users@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-users
