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Subject: Re: [OMPI devel] Warnings from pgcc-13.10
From: Larry Baker (baker_at_[hidden])
Date: 2014-01-17 14:44:13


Paul,

From what I can see in the arguments to OPAL_OUTPUT_VERBOSE() in line 356 at https://bitbucket.org/ompiteam/ompi-svn-mirror/src/f48eeda443104a64dc89e4f5fab4c940e44d8615/opal/mca/db/hash/db_hash.c, this is the same PGI bug I reported 22 Jul 2010, which was assigned TPR 17139.

> Customer information:
>
> Larry Baker
> US Geological Survey
> 650-329-5608
> baker_at_[hidden]
>
> Product: 2183-WS
> PIN: 507549
>
> Problem description:
>
> I am trying to track down the warnings that occur when compiling the UCAR NetCDF package with PGI compilers. I have found a case that gcc does not warn about, but pgcc does. If I understand the code and the C (1990) standard, I think pgcc is complaining too much.
>
> You can reproduce the warnings by downloading the UCAR NetCDF source package, netcdf.tar.gz, fromhttp://www.unidata.ucar.edu/software/netcdf/. Assuming you download it to /usr/local/src, here are the commands that illustrate the warnings:
>
> # cd /usr/local/src
> # tar -xzf netcdf.tar.gz
> # cd netcdf-4.1.1
> # ./configure >/dev/null 2>&1
> # cd ncgen
> # pgcc -DHAVE_CONFIG_H -I. -I.. -I../fortran -I.. -I../libsrc -I../libsrc -g -O2 -tp amd64 -Msignextend -DNO_PGI_OFFSET -c -o genf77.o genf77.c
> PGC-W-0095-Type cast required for this conversion (genf77.c: 498)
> PGC-W-0095-Type cast required for this conversion (genf77.c: 511)
> PGC/x86-64 Linux 10.3-0: compilation completed with warnings
>
> To eliminate the warnings, I had to modify the two source lines to cast the result from static const char* f77varncid() as (char *):
>
>> /* Use the specialized put_att_XX routines if possible*/
>> switch (basetype->typ.typecode) {
>> case NC_BYTE:
>> case NC_SHORT:
>> case NC_INT:
>> case NC_FLOAT:
>> case NC_DOUBLE:
>> f77attrify(asym,code);
>> codedump(code);
>> bbClear(code);
>> bbprintf0(stmt,"stat = nf_put_att_%s(ncid, %s, %s, %s, %lu, %sval)\n",
>> nfstype(basetype->typ.typecode),
>> (asym->att.var == NULL?"NF_GLOBAL"
>> :(char *) f77varncid(asym->att.var)), <--- here
>> f77escapifyname(asym->name),
>> nftype(basetype->typ.typecode),
>> len,
>> ncftype(basetype->typ.typecode));
>> codedump(stmt);
>> break;
>>
>> case NC_CHAR:
>> len = bbLength(code);
>> f77quotestring(code);
>> bbprintf0(stmt,"stat = nf_put_att_text(ncid, %s, %s, %lu, ",
>> (asym->att.var == NULL?"NF_GLOBAL"
>> :(char *)f77varncid(asym->att.var)), <--- and here
>> f77escapifyname(asym->name),
>> (len==0?1:len));
>> codedump(stmt);
>> codedump(code);
>> codeline(")");
>> break;
>
> Here is static const char* f77varncid():
>
>> /* Compute the name for a given var's id*/
>> /* Watch out: the result is a static*/
>> static const char*
>> f77varncid(Symbol* vsym)
>> {
>> const char* tmp1;
>> char* vartmp;
>> tmp1 = f77name(vsym);
>> vartmp = poolalloc(strlen(tmp1)+strlen("_id")+1);
>> strcpy(vartmp,tmp1);
>> strcat(vartmp,"_id");
>> return vartmp;
>> }
>
> There are other lines in genf77.c that use f77varncid() in a print statement, so the warnings do not occur every time f77varncid() provides a string for %s:
>
>> if (nvars > 0) {
>> f77skip();
>> f77comment("variable ids");
>> for(ivar = 0; ivar < nvars; ivar++) {
>> Symbol* vsym = (Symbol*)listget(vardefs,ivar);
>> bbprintf0(stmt,"integer %s;\n", f77varncid(vsym));
>> codedump(stmt);
>> }
>
> The warnings occur in the only two instances where f77varncid() is used in a conditional expression. In both cases, the second operand is a literal string, e.g., "NF_GLOBAL". I would have thought that a (static const char*) and a string literal would be compatible types. I experimented with a (const char *) cast instead of a (char *) cast, but that does not work. I think it should.
>
> I admit, I have an old copy of the C standard — from 1990. But, here's my interpretation of what it says about this:
>
> • 6.1.4 String literals, says string literals are converted to an array of type char. If the program attempts to modify a string literal, the behavior is undefined. It does not say that the type has the const type qualifier (though, you would think it should).
>
> • 6.3.15 Conditional operator, says if the second and third operands are pointers ..., the result type is a pointer to a type qualified with all the type qualifiers of the types pointed-to by both operands.
>
> This would seem to explain the warning message, since the string literal is (char *) and f77varncid() is (const char *). However, 6.3.15 goes on to say:
>
> Furthermore, if both operands are pointers to ... differently qualified versions of a compatible type, the result has the composite type.
>
> Which leads me to believe you are allowed to mix const and non-const versions of a compatible type.
>
> Lastly:
>
> • 6.5.3 Type qualifiers, says that the properties associated with qualified types are meaningful only for expressions that are lvalues.
>
> Seems to make the issue moot, since it says const-ness only applies to lvalues.
>
> So, I think both 6.3.15 and 6.5.3 imply that (char *) and (const char *) are compatible as the second and third operands in a conditional expression which is not an lvalue, which is the case in this code. As I mentioned above, gcc does not complain about this code. What do you think?
>
> Larry Baker
> US Geological Survey
> 650-329-5608
> baker_at_[hidden]

I could inquire about the current status of this TPR if you like. (Might as well.)

Larry Baker
US Geological Survey
650-329-5608
baker_at_[hidden]

On 17 Jan 2014, at 11:28 AM, Paul Hargrove wrote:

> Ralph,
>
> You are probably right that the string literals are a likely cause (type char[] ? ).
> I will poke at this a bit by adding (char *) casts to see which argument(s) are actually the cause and get back to you.
>
> -Paul
>
>
> On Fri, Jan 17, 2014 at 8:56 AM, Ralph Castain <rhc_at_[hidden]> wrote:
> Hi Paul
>
> Looking at these, I'm a tad puzzled. It would appear that PGI is complaining about the fixed string being passed in the last three cases as there is no (const char*)foo being used in those areas. Yet we use that same logic elsewhere and your report isn't showing those as warnings.
>
> Do you think it is the fixed string that is the issue - or is it the (const char*) variable we need to recast?
>
>
> On Jan 16, 2014, at 11:24 PM, Paul Hargrove <phhargrove_at_[hidden]> wrote:
>
>> My builds of the trunk with pgcc-13.10 turned up the following warnings:
>>
>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 354)
>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 376)
>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 452)
>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/opal/mca/db/hash/db_hash.c: 534)
>>
>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/orte/mca/state/base/state_base_fns.c: 766)
>>
>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/orte/mca/plm/rsh/plm_rsh_component.c: 368)
>>
>> PGC-W-0095-Type cast required for this conversion (/scratch/scratchdirs/hargrove/OMPI/openmpi-trunk-linux-x86_64-pgi-13.10/openmpi-1.9a1r30302/orte/mca/plm/rsh/plm_rsh_module.c: 1337)
>>
>> I believe all of these are related to passing a (const char *) to OPAL_OUTPUT_VERBOSE().
>>
>> -Paul
>>
>>
>> --
>> Paul H. Hargrove PHHargrove_at_[hidden]
>> Future Technologies Group
>> Computer and Data Sciences Department Tel: +1-510-495-2352
>> Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
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>
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>
> --
> Paul H. Hargrove PHHargrove_at_[hidden]
> Future Technologies Group
> Computer and Data Sciences Department Tel: +1-510-495-2352
> Lawrence Berkeley National Laboratory Fax: +1-510-486-6900
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