[Bug c++/61596] -Wunused-local-typedefs warns incorrectly on a typedef that's referenced indirectly

["thakis at chromium dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61596

--- Comment #2 from thakis at chromium dot org ---
Here's a similar example that doesn't need C++1y, regular C++11 is sufficient:

thakis@ubu:~$ cat test.cc
template <class T>
void template_fun(T t) {
  typename T::Foo s3foo;  // YYY
  (void)s3foo;
}
void template_fun_user() {
  struct Local {
    typedef int Foo;  // XXX
  } p;
  template_fun(p);
}
thakis@ubu:~$ g++ -c test.cc -std=c++11 -Wall
test.cc: In function ‘void template_fun_user()’:
test.cc:8:17: warning: typedef ‘template_fun_user()::Local::Foo’ locally
defined but not used [-Wunused-local-typedefs]
     typedef int Foo;
                 ^


Maybe a possible fix is to store all typedefs that get this warning as
candidates, and then emit warnings at the end of the translation unit for all
candidates that are still unreferenced at that point.
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From: "ishiura-compiler at ml dot kwansei.ac.jp" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/61931] New: Wrong Constant Folding
Date: Mon, 28 Jul 2014 04:34:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida931

            Bug ID: 61931
           Summary: Wrong Constant Folding
           Product: gcc
           Version: 4.8.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ishiura-compiler at ml dot kwansei.ac.jp

GCC 4.8.4 for arm miscompiles the following code.

  $ cat test.c

  int a, b, c, d, e, f, g, h;
  long long i;
  int
  main (void)
  {
    int j;
    i = a - ((((b | ((1LL * c) >> 1)) / 3) | (1 << (1 / (e + 1)))) | 1);
    j = ((((1 % (1LLU << f)) & (((1LLU >> h)) - (63LLU * d)))) << 1) == ((1LL %
(g + 1)) * a);
    if (i == 1);
    else
    __builtin_printf ("%lld, j = %lld\n", 0, j);
  }

  $ arm-none-eabi-gcc-4.8.4 test.c -o test.out -O1 --specs=rdimon.specs
  $ qemu-arm -L /usr/arm-linux-gnueabihf/ ./test.out
  1, j = 0

  $ arm-none-eabi-gcc-4.8.4 test.c -o test.out -O0 --specs=rdimon.specs
  $ qemu-arm -L /usr/arm-linux-gnueabihf/ ./test.out
  -12884901887, j = 0

  $ arm-none-eabi-gcc-4.8.4 -v
  Using built-in specs.
  COLLECT_GCC=arm-none-eabi-gcc-4.8.4

COLLECT_LTO_WRAPPER=/home/ishiuraken/gcc-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/4.8.4/lto-wrapper
  Target: arm-none-eabi
  Configured with: /home/build/work/GCC-4-8-build/src/gcc/configure
--target=arm-none-eabi --prefix=/home/build/work/GCC-4-8-build/install-native
--libexecdir=/home/build/work/GCC-4-8-build/install-native/lib
--infodir=/home/build/work/GCC-4-8-build/install-native/share/doc/gcc-arm-none-eabi/info
--mandir=/home/build/work/GCC-4-8-build/install-native/share/doc/gcc-arm-none-eabi/man
--htmldir=/home/build/work/GCC-4-8-build/install-native/share/doc/gcc-arm-none-eabi/html
--pdfdir=/home/build/work/GCC-4-8-build/install-native/share/doc/gcc-arm-none-eabi/pdf
--enable-languages=c,c++ --enable-plugins --disable-decimal-float
--disable-libffi --disable-libgomp --disable-libmudflap --disable-libquadmath
--disable-libssp --disable-libstdcxx-pch --disable-nls --disable-shared
--disable-threads --disable-tls --with-gnu-as --with-gnu-ld --with-newlib
--with-headers=yes --with-python-dir=share/gcc-arm-none-eabi
--with-sysroot=/home/build/work/GCC-4-8-build/install-native/arm-none-eabi
--build=i686-linux-gnu --host=i686-linux-gnu
--with-gmp=/home/build/work/GCC-4-8-build/build-native/host-libs/usr
--with-mpfr=/home/build/work/GCC-4-8-build/build-native/host-libs/usr
--with-mpc=/home/build/work/GCC-4-8-build/build-native/host-libs/usr
--with-isl=/home/build/work/GCC-4-8-build/build-native/host-libs/usr
--with-cloog=/home/build/work/GCC-4-8-build/build-native/host-libs/usr
--with-libelf=/home/build/work/GCC-4-8-build/build-native/host-libs/usr
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm'
--with-pkgversion='GNU Tools for ARM Embedded Processors'
--with-multilib-list=armv6-m,armv7-m,armv7e-m,armv7-r
  Thread model: single
  gcc version 4.8.4 20140526 (release) [ARM/embedded-4_8-branch revision
211358] (GNU Tools for ARM Embedded Processors)