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From: "bobmiller at nvidia dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/100279] New: Invalid generated assembly for NTTP lambda
 with negative double value
Date: Tue, 27 Apr 2021 01:33:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100279

            Bug ID: 100279
           Summary: Invalid generated assembly for NTTP lambda with
                    negative double value
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bobmiller at nvidia dot com
  Target Milestone: ---

Created attachment 50683
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D50683&action=3Dedit
The preprocessed file that triggers the bug

I've stumbled across an obscure behavior that results in incorrect assembly
generation: the same signature is generated twice, which the assembler later
(correctly) rejects. I've tested this on GCC-11 and trunk, on my own machine
and godbolt ( example here: https://godbolt.org/z/6eEnKca9o )

Minimal example:=20
----------------------------
template<auto V> struct T {};

template<class F> void E(F &&) {}

template<auto V, decltype(V)...Vs, class F>
void E(F &&f)
{
    f(T<V>{});
    E<Vs...>(f);
}

void foo()
{
    E<-1.0, -2.0>(
    [&]<auto X>(T<X>){});
}

int main(int, char**) {}
--------------------------

Interestingly, this does NOT occur for floats or long doubles: only doubles:
changing the suffixes of -1.0 and -2.0 above to -1.0f and -2.0f (or -1.0L a=
nd
-2.0L) results in valid generated code.

------------------
Output from gcc -v:

COLLECT_GCC=3Dg++-11
COLLECT_LTO_WRAPPER=3D/home/bob/libexec/gcc/x86_64-linux-gnu/12.0.0/lto-wra=
pper
Target: x86_64-linux-gnu
Configured with: ../gcc/configure -v --build=3Dx86_64-linux-gnu
--host=3Dx86_64-linux-gnu --target=3Dx86_64-linux-gnu --prefix=3D/home/bob/
--enable-checking=3Drelease --enable-languages=3Dc,c++ --disable-multilib
--program-suffix=3D-11
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20210426 (experimental) (GCC)=20


Command line to trigger bug: g++-11 --std=3Dc++20 bugtest.cpp -o test

Compiler output:
/tmp/ccmrd0Wr.s: Assembler messages:
/tmp/ccmrd0Wr.s:106: Error: symbol
`_ZZ3foovENKUl1TIXT_EEE_clILdffffffff00000000EEEDaS0_' is already defined=