[Bug c++/61362] g++ (Ubuntu 4.8.2-19ubuntu1) 4.8.2 does not compile lambda with template

["thibaut.lutz at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61362

--- Comment #6 from Thibaut LUTZ <thibaut.lutz at googlemail dot com> ---
My previous test cases still fails with 6.0.0 20151012 on linux64.
It passes with "-std=c++11".
Fails with "-std=c++14", "-std=c++17", "-std=c++1y".

Same error:
prog.cc: In instantiation of ‘struct S<int>::<lambda()>’:
prog.cc:3:29:   required from here
prog.cc:3:10: internal compiler error: in tsubst_copy, at cp/pt.c:13708
   int f{[this](){return 42;}()};
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From: "ktkachov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/67929] New: [4.9/5/6 Regression][arm] Wrong code for FP mult-by-power-of-2 + int conversion
Date: Mon, 12 Oct 2015 10:57:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg929

            Bug ID: 67929
           Summary: [4.9/5/6 Regression][arm] Wrong code for FP
                    mult-by-power-of-2 + int conversion
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ktkachov at gcc dot gnu.org
  Target Milestone: ---
            Target: arm*

Testcase:

int
foo (float a)
{
  return a * 4.9f;
}


int
main (void)
{
  if (foo (10.0f) != 49)
    __builtin_abort ();

  return 0;
}

Compiled with -Ofast -mfpu=vfpv3 -mfloat-abi=hard -mcpu=cortex-a15 -fno-inline
aborts.

The problem is foo (10.0f) returns 40.
This is because the combine_vcvtf2i triggers where its predicate should have
rejected 4.9f

The vfp3_const_double_for_bits function in arm.c is too liberal and accepts any
FP constant that, when truncated, evaluates to a power of 2 FP constant.