Get rid of “type qualifier” warnings on functions using the restrict keyword

问题

I'm trying to clean up warnings that I'm getting when compiling Blitz++ of the form:

/opt/local/include/blitz/tinyvec2.h:261:35: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
/opt/local/include/blitz/tinyvec2.h:264:43: warning: type qualifiers ignored on function return type [-Wignored-qualifiers] 
/opt/local/include/blitz/tinyvec2.h:267:40: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]
<<etc.>>

From these kinds of member functions (of the TinyVector class)

T_numtype * restrict data()    // line 261                      
    { return data_; }          // data is a member that is an array of data values

const T_numtype * restrict data() const       // line 264       
    { return data_; }

As far as I can tell I am getting the warnings due to the restrict keyword. Note: there are macros that should replace the restrict with __restrict__ (which g++ understands).

I can get rid of the warnings by deleting the keywords; however, since this is supposed to be a high-performance numerical library, I don't want to lose any compiler optimizations that the restrict keywords are allowing.

What can I do to suppress these warnings without just dropping the restrict's altogether, and while keeping -Wall on?

回答1:

^README

^{__restrict__ has no usage on return-types, which is exactly why gcc is giving you the diagnostic. The keyword is used to signal that two pointers passed to a function doesn't point to the same object, ie. that they are unique; changing one will not affect the other. This can greatly improve optimizations, but it's worth noting that it won't affect the returned value of a function.}

^{There's no reason for you to apply __restrict__ on the return type.}

^{The above README is written by me, I used quotations to draw some extra attention to it since the information contained is important to the matter at hand..}

Ignore warning using gcc specific pragma

You could ask gcc to disregard diagnostics matching -Wignored-qualifiers by using diagnostic pragmas.

Diagnostic Pragmas - Using the GNU Compiler Collection (gcc)

Ignore it everywhere

This will ignore every warning that -Wignored-qualifiers would enable;

#pragma GCC diagnostic ignored "-Wignored-qualifiers"

Ignore it for a seleted area

This will ignore -Wignored-qualifiers related warnings for the code replaced by ...

... // warnings enabled

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wignored-qualifiers"

... // warning disabled here

#pragma GCC diagnostic pop

... // warnings enabled again

^{Note: -Wignored-qualifiers is enabled through -Wextra, not -Wall.}

来源：https://stackoverflow.com/questions/23961279/get-rid-of-type-qualifier-warnings-on-functions-using-the-restrict-keyword

标签

c++

g++

suppress-warnings

restrict-qualifier

blitz++