[Bug tree-optimization/84203] New: add -Wsuggest-attribute=returns_nonnull

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84203

            Bug ID: 84203
           Summary: add -Wsuggest-attribute=returns_nonnull
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

The option -Wsuggest-attribute= helps improve code generation by annotating
function declarations with attributes like cold, const, pure, malloc and
noreturn.  However, the option doesn't make it possible to request suggestions
for the returns_nonnull attribute.  Especially in C++ where functions returning
newly allocated memory often never return null (because they throw on failure
to allocate), making use of the attribute could further improve generated code.

$ cat t.C && gcc -Wall -Wextra -O -S -Wsuggest-attribute=noreturn t.C
int f ()   // -Wsuggest-attribute=noreturn here (good)
{
  throw "not implemented";
}


void* f (unsigned n)   // missing -Wsuggest-attribute=returns_nonnull
{
  return new char[n];
}

t.C: In function ‘int f()’:
t.C:1:5: warning: function might be candidate for attribute ‘noreturn’
[-Wsuggest-attribute=noreturn]
 int f ()   // -Wsuggest-attribute=noreturn here (good)
     ^