[Bug c++/61412] New: Warnings incorrectly suppressed when compiling previously preprocessed file

[Bug c++/61412] New: Warnings incorrectly suppressed when compiling previously preprocessed file

[matt at godbolt dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

            Bug ID: 61412
           Summary: Warnings incorrectly suppressed when compiling
                    previously preprocessed file
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: matt at godbolt dot org

Some warnings appear to be lost when compiling a previously-preprocessed source
file (e.g. as a result of using ccache, which caches the intermediate
preprocessed source). A minimal example (of a post-preprocessed file):

--begin example
# 88 "some/file.cpp" 3 4
struct Foo { int i, j; Foo() : j(1), i(0) {} };
--end example

compiled with: "g++ -c -Wall -Wextra -Werror -o /tmp/foo /tmp/pp.ii" there is
no warning or error about the reordered initializer.  However, removing the
first line (the # directive) to yield:

--begin example2
struct Foo { int i, j; Foo() : j(1), i(0) {} };
--end example2

gives the error, as expected:
/tmp/pp.ii: In constructor ‘Foo::Foo()’:
/tmp/pp.ii:2:21: error: ‘Foo::j’ will be initialized after [-Werror=reorder]
 struct Foo { int i, j; Foo() : j(1), i(0) {} };
                     ^
/tmp/pp.ii:2:18: error:   ‘int Foo::i’ [-Werror=reorder]
 struct Foo { int i, j; Foo() : j(1), i(0) {} };
                  ^
/tmp/pp.ii:2:24: error:   when initialized here [-Werror=reorder]
 struct Foo { int i, j; Foo() : j(1), i(0) {} };
                        ^

GCC version:
$ g++ -v
Using built-in specs.
COLLECT_GCC=/home/mgodbolt/.fighome/runtime/gcc/4.9.0-2/bin/g++
COLLECT_LTO_WRAPPER=/mnt/data/fighome/runtime/gcc/4.9.0-2/bin/../libexec/gcc/x86_64-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../gcc-4.9.0/configure --prefix
/data/teamcity/work/sud-chibld05-002-RHEL6/9d49ff0b2777552a/scratch/gcc/4.9.0/staging
--build=x86_64-linux-gnu --disable-multilibs --enable-clocale=gnu
--enable-languages=c,c++ --enable-ld=yes --enable-gold=yes
--enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-linker-build-id
--enable-lto --enable-plugins --enable-threads=posix --host=x86_64-linux-gnu
--target=x86_64-linux-gnu --with-pkgversion=DRW-internal-build
--with-system-zlib --disable-werror
--with-libelf=/data/teamcity/work/sud-chibld05-002-RHEL6/9d49ff0b2777552a/scratch/gcc/4.9.0/build/libelf-0.8.13
Thread model: posix
gcc version 4.9.0 (DRW-internal-build) 

Running on Linux.  Does not happen with GCC 4.7.2.
>From gcc-bugs-return-453209-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Wed Jun 04 15:01:42 2014
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From: "dominiq at lps dot ens.fr" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/61387] [4.10 Regression] ~900 test failures on on x86_64-apple-darwin13 for g++ with -m64 after r211088
Date: Wed, 04 Jun 2014 15:01:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida387

--- Comment #5 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
(In reply to Iain Sandoe from comment #4)
> 3.
>
> Anyway, assuming that the intention is to unwrap the indirection from the call
> - something like: ...

The following patch fixes the failures (not counting new ones:
g++.dg/debug/dwarf2/imported-decl-2.C and g++.dg/tls/diag-1.C).

--- ../_clean/gcc/config/i386/i386.c    2014-06-04 00:42:24.000000000 +0200
+++ gcc/config/i386/i386.c    2014-06-04 15:05:42.000000000 +0200
@@ -38898,7 +38898,9 @@ x86_output_mi_thunk (FILE *file,
     {
       if (sibcall_insn_operand (fnaddr, word_mode))
     {
-      tmp = gen_rtx_CALL (VOIDmode, fnaddr, const0_rtx);
+      fnaddr = XEXP (DECL_RTL (function), 0);
+      tmp = gen_rtx_MEM (QImode, fnaddr);
+      tmp = gen_rtx_CALL (VOIDmode, tmp, const0_rtx);
           tmp = emit_call_insn (tmp);
           SIBLING_CALL_P (tmp) = 1;
     }

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Matt Godbolt from comment #0)
> Does not happen with GCC 4.7.2.

Are you sure?

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[matt at godbolt dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

--- Comment #3 from Matt Godbolt <matt at godbolt dot org> ---
Many apologies: this does indeed also happen with GCC 4.7.2! Thanks for
checking.

Also, re: the -Wsystem-headers, this does indeed fix this case but of course in
general isn't a good workaround as system headers often do have warnings.

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Matt Godbolt from comment #0)
> --begin example
> # 88 "some/file.cpp" 3 4
> struct Foo { int i, j; Foo() : j(1), i(0) {} };
> --end example

How did you produce that file?  If you compile the exact preprocessor output
you shouldn't have a problem. If you mangle it, fooling the compiler into
thinking it's in a system header, you have a problem.

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[matt at godbolt dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

--- Comment #5 from Matt Godbolt <matt at godbolt dot org> ---
I produced the file by preprocessing an existing file with g++ -E on an
existing file that exhibited the file (250k+ lines).

The full line I used to create the original preprocessed file is:
$ g++ -c -std=gnu++1y -ggdb3 -Wall -Wextra -Werror -fdiagnostics-show-option
-Wno-unused-local-typedefs -DBOOST_ASIO_DISABLE_EVENTFD -DBOOST_OKAY
-march=core2 -Isrc -isystem include -O3 -DNDEBUG -DBOOST_ASIO_DISABLE_ASSERTS
-DBOOST_DISABLE_ASSERTS -MMD -MP -MFout/main/helix/HelixRegressionModule.d -MT
out/main/helix/HelixRegressionModule.o
-MTout/main/helix/HelixRegressionModule.d -E
src/helix/HelixRegressionModule.cpp

That 250K+ file also exhibits the problem: that is, the warning is suppressed
even within the main body of the file. I then whittled down the preprocessed
file to just those two lines. In the original file the "# ..." line came from
the middle of a macro expansion defined by a header included via an -isystem
path. The filename in the "# " line refers to the C++ file though in both
cases.

The macro is a LOG4CPLUS macro and it expands in the original file to:

        if (numSkipped)
            do { if((L).isEnabledFor(log4cplus::WARN_LOG_LEVEL)) {
log4cplus::tostringstream _log4cplus_buf; _log4cplus_buf << "Skipped " <<
numSkipped << " orders due to juncture mismatches, erf target=" << juncture <<
" hdf5 epoch now=" << (row < numRows? records[row].epoch:0);
(L).forcedLog(log4cplus::WARN_LOG_LEVEL, _log4cplus_buf.str(),


 "src/helix/HelixRegressionModule.cpp"
# 88 "src/helix/HelixRegressionModule.cpp" 3 4
            ,


 91
# 88 "src/helix/HelixRegressionModule.cpp" 3 4
            ); } } while (0)


                                                             ;

where line 88 of the original file is:
        if (numSkipped)
            LOG4CPLUS_WARN(L, "Skipped " << numSkipped
                    << " orders due to juncture mismatches, erf target="
                    << juncture << " hdf5 epoch now="
                    << (row < numRows? records[row].epoch:0));


I had not previously encountered the "#" directive with trailing numbers so it
aroused my suspicion. That made me hone in on it and discover that just the "#"
directive alone is enough to seemingly convince GCC that what follows is a
system header.

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[schwab@linux-m68k.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

--- Comment #6 from Andreas Schwab <schwab@linux-m68k.org> ---
May be a dup of bug 57201.

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
cat > sys/h.h <<EOT
#define X(I) char c = { I }
EOT
cat > C.C << EOT
#include <h.h>
int main () {
  int i = 256;
  X(i);
}
EOT
g++ -isystem sys C.C -Wall
g++ -isystem sys C.C -Wall -Wsystem-headers
In file included from C.C:1:0:
C.C: In function ‘int main()’:
C.C:4:3: warning: narrowing conversion of ‘i’ from ‘int’ to ‘char’ inside { }
is ill-formed in C++11 [-Wnarrowing]
   X(i);
   ^
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From: "matt at godbolt dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file
Date: Wed, 04 Jun 2014 17:04:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida412

--- Comment #12 from Matt Godbolt <matt at godbolt dot org> ---
I appreciate your patience on this! I'm also now confused.  My 250k+
preprocessed file does not warn on a reordered constructor initializer, despite
there being no system code or macros involved in it.  Compiling the original
file (not the preprocessed version) directly warns as expected.

While attempting the reduce to an absolute minimal case I found the (or maybe
just one) issue that caused the suppression of the warning was the "#" line.
This is many hundreds of lines above the constructor and its initializer and is
unconnected to a system include.

The "#" line itself refers only to a non-system file, which confuses me.

I will try and get a non-preprocessed reproducible case to try and clear up any
confusion.

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Matt Godbolt from comment #12)
> Compiling the
> original file (not the preprocessed version) directly warns as expected.

Ah I misunderstood that part, sorry.

[Bug c++/61412] Warnings incorrectly suppressed when compiling previously preprocessed file

[matt at godbolt dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61412

Matt Godbolt <matt at godbolt dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE

--- Comment #14 from Matt Godbolt <matt at godbolt dot org> ---
(In reply to Manuel López-Ibáñez from comment #9)
> but maybe it is a dup of PR60723.

It does indeed look like this. My reproduction attempts all failed until I put
a newline into my macro, which then triggers output like '# "file.cpp" 4 3'
after the newlines, which then causes suppression of warnings downstream.

I'll mark this bug as a duplicate, thanks for spotting it!

*** This bug has been marked as a duplicate of bug 60723 ***
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Subject: [Bug preprocessor/60723] Line directives with incorrect system header flag
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id`723

Matt Godbolt <matt at godbolt dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matt at godbolt dot org

--- Comment #6 from Matt Godbolt <matt at godbolt dot org> ---
*** Bug 61412 has been marked as a duplicate of this bug. ***