[cfe-commits] r161501 - in /cfe/trunk: include/clang/AST/Expr.h include/clang/Basic/DiagnosticGroups.td include/clang/Basic/DiagnosticSemaKinds.td lib/AST/Expr.cpp lib/Sema/SemaExpr.cpp lib/Sema/SemaOverload.cpp test/SemaCXX/constant-expression-c

[Jordan Rose]

On Aug 17, 2012, at 15:43 , David Blaikie <dblaikie at gmail.com> wrote:

> On Fri, Aug 17, 2012 at 3:33 PM, Nico Weber <thakis at chromium.org> wrote:
>> Should this really be on by default? On chrome, this triggers a single
>> time (linux-only):
>> 
>> ../../third_party/tcmalloc/chromium/src/stack_trace_table.cc:138:16:
>> warning: expression which evaluates to zero treated as a null pointer
>> constant of type 'void *' [-Wnon-literal-null-conversion]
>>  out[idx++] = static_cast<uintptr_t>(0);
>>               ^~~~~~~~~~~~~~~~~~~~~~~~~
>> 
>> out is declared as `void** out = new void*[out_len];`. The warning
>> isn't wrong, but it looks rather pedantic to me. Should this be only
>> in -Wall (or maybe even in -pedantic)?
> 
> Might be a fair candidate for -Wall, though it did find some
> reasonable stuff in google. 18 cases overall with some fairly
> interesting ones (see b/6954211 for the ones that've been committed so
> far, or cl/32692314 for some of the remaining ones.
> 
> The worst offenders are integer constants with value 0 that aren't at
> all intended to be pointers. (most easily occurred in function calls
> where the caller thought the argument was of one type but it's
> actually of a pointer type)
> 
> I have some more once this warning opens up to cover comparisons,
> conditional operands, and return statements - there's a lot of
> confusing "cstr == '\0'" code where the user probably meant to deref
> the lhs but didn't.

IMHO, this should remain on by default. The Chromium example clearly shows an impedance mismatch between the array and the value being stored. I would say it's not unlikely that at one point the array was a uintptr_t*, but was changed, and this part of the code wasn't updated to match because it didn't warn. But I can see the argument that "because this isn't harmful, we shouldn't warn unless asked to".