[Bug c++/61937] New: Misleading errors due to constructor template deducing argument as void

[Bug c++/61937] New: Misleading errors due to constructor template deducing argument as void

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61937

            Bug ID: 61937
           Summary: Misleading errors due to constructor template deducing
                    argument as void
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: minor
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org

template<typename T, typename U = void>
  struct trait;

template<typename T>
  struct trait<T, T>
  {
  using type = T;
  };

template<typename T>
  struct trait<T, void>
  {
    using type = T;
  };

struct S {
  template<typename T, typename U = typename trait<T>::type>
    S(const T&) { }
};

void f() { }

S s = f();

Compiling with -std=c++11 gives four errors:

void.cc: In substitution of ‘template<class T, class U> S::S(const T&) [with T
= void; U = <missing>]’:
void.cc:23:9:   required from here
void.cc:17:24: error: ambiguous class template instantiation for ‘struct
trait<void, void>’
   template<typename T, typename U = typename trait<T>::type>
                        ^
void.cc:5:10: error: candidates are: struct trait<T, T>
   struct trait<T, T>
          ^
void.cc:11:10: error:                 struct trait<T, void>
   struct trait<T, void>
          ^
void.cc:23:9: error: conversion from ‘void’ to non-scalar type ‘S’ requested
 S s = f();
         ^

Only the last one is relevant and useful, the others are just confusing.

The first three errors are due to instantiating the constructor template with T
= void but that doesn't make much sense. It implies the function f() returns an
object of type void, rather than returning nothing.
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From: "harmeeksingh at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/61938] New: Vectorization not happening .
Date: Mon, 28 Jul 2014 19:11:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ida938

            Bug ID: 61938
           Summary: Vectorization not happening .
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: harmeeksingh at gmail dot com

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.7.2/lto-wrapper
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --disable-build-with-cxx
--disable-build-poststage1-with-cxx --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions --enable-gnu-unique-object
--enable-linker-build-id --with-linker-hash-style=gnu
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada,go,lto --enable-plugin
--enable-initfini-array --enable-java-awt=gtk --disable-dssi
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-ppl --with-cloog --with-tune=generic --with-arch_32=i686
--build=x86_64-redhat-linux
Thread model: posix
gcc version 4.7.2 20120921 (Red Hat 4.7.2-2) (GCC)


Testcase

#include <stdio.h>

#define VEC 1024

typedef long int int64;
typedef int int32;

void foo (int       arraysize,
          int       *result,
          int       *selectvector,
          int       selectelements,
          int32     *array,
          int32     compval)
{
  int k, i;
  for (k =0,i=0; i < selectelements; ++i) {
      result[k] = selectvector[i]; k += (((array[selectvector[i]])) =compval);
  }
}

main()
{
  int       result[VEC];
  int       selectvector[VEC];
  int       selectelements;
  int32     array[VEC];

  int k, i;
  foo(VEC, &result[0], &selectvector[0], VEC, &array[0], 1);
}

Compilation log
gcc -fPIC -ggdb -O3 -march=native -ftree-vectorize -ftree-vectorizer-verbose=7
/tmp/x.c -o /tmp/x

Analyzing loop at /tmp/x.c:17

17: not vectorized: data ref analysis failed *D.2502_9 = D.2506_14;

17: not vectorized: data ref analysis failed *D.2502_9 = D.2506_14;

/tmp/x.c:9: note: vectorized 0 loops in function.

[Bug c++/61937] Misleading errors due to constructor template deducing argument as void

[ville.voutilainen at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61937

Ville Voutilainen <ville.voutilainen at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-12-14
                 CC|                            |ville.voutilainen at gmail dot com
     Ever confirmed|0                           |1