cxx-ada-int128-types

C++ Ada unsigned __int128 types

GCC 13 and 14 emit the internal C++ name for unsigned __int128 as an undefined Ada identifier.

AcceptedApplies standaloneSince 1.2.0

Bundle JSON Repository directory

Where it applies.

How each patchset treats this bundle on each GCC major
PatchsetGCC 13GCC 14GCC 15GCC 16
1.2.0 (latest)Patchedgcc-13-1413.2.0Patchedgcc-13-1414.2.0Known-good control15.3.0Known-good control16.2.0
1.1.0Not applicable13.2.0Not applicable14.2.0Not applicable15.3.0Not applicable16.2.0
1.0.1Not applicable13.2.0Not applicable14.2.0Not applicable15.3.0Not applicable16.1.0
1.0.0Not applicable13.2.0Not applicable14.2.0Not applicable15.3.0Not applicable16.1.0

Explanation.

GCC 13 and 14 special-case the internal C++ type name __int128, but compare the complete spelling. That recognizes the signed type and misses the internal unsigned spelling, __int128 unsigned.

The offending C++ is:

using Signed_128 = __int128;
using Unsigned_128 = unsigned __int128;

Signed_128 signed_round_trip (Signed_128);
Unsigned_128 unsigned_round_trip (Unsigned_128);

The GCC 13/14 mapper currently produces one valid subtype and one reference to an Ada identifier that does not exist:

subtype Signed_128 is Extensions.Signed_128;
subtype Unsigned_128 is uu_int128_unsigned;

It should recognize both internal names as 128-bit integer types and produce:

subtype Signed_128 is Extensions.Signed_128;
subtype Unsigned_128 is Extensions.Unsigned_128;

The correction uses the eight-character __int128 prefix comparison already present in GCC 15 and 16. Those releases are known-good controls and receive no code patch. The executable regression passes negative signed and high-bit unsigned values by value from C++ to Ada, back through C++, and into C++ value checkers at -O0 and -O2.

Run it against an unpatched or patched compiler root:

./bundles/cxx-ada-int128-types/run-test.sh \
  TOOLCHAIN_ROOT GCC_VERSION unpatched
./bundles/cxx-ada-int128-types/run-test.sh \
  TOOLCHAIN_ROOT GCC_VERSION patched

Patch.

Variant gcc-13-14

Applies to 13.2.0, 14.2.0. Source flavors: linux, darwin_arm64.

+24 −2 2 files

SHA-256
0ff464719272eaf8ea9696a06e91338c9e77c33e71cbc565493a2c044a3e5969
Patch
bundles/cxx-ada-int128-types/patches/gcc-13-14.patch

Download the patch

gcc/c-family/c-ada-spec.cc +2−2modified
@@ -2193 +2193 @@dump_ada_node (pretty_printer *buffer, tree node, tree type, int spc,
2193 && !strcmp (IDENTIFIER_POINTER (DECL_NAME (TYPE_NAME (node))),
2194 "__int128")))
2193 && !strncmp (IDENTIFIER_POINTER (DECL_NAME (TYPE_NAME (node))),
2194 "__int128", 8)))
gcc/testsuite/g++.dg/ada-spec/int128-types.C +22−0new file
@@ -0 +1 @@
1/* { dg-do compile } */
2/* { dg-options "-fdump-ada-spec-slim" } */
3/* { dg-final { scan-file int128_types_c.ads "subtype Signed_128 is Extensions.Signed_128" } } */
4/* { dg-final { scan-file int128_types_c.ads "subtype Unsigned_128 is Extensions.Unsigned_128" } } */
5
6using Signed_128 = __int128;
7using Unsigned_128 = unsigned __int128;
8
9static const Signed_128 signed_expected
10 = -((static_cast<Signed_128> (1) << 100) + 12345);
11static const Unsigned_128 unsigned_expected
12 = (static_cast<Unsigned_128> (1) << 127)
13 | (static_cast<Unsigned_128> (1) << 80) | 67890;
14
15Signed_128 signed_seed () { return signed_expected; }
16Unsigned_128 unsigned_seed () { return unsigned_expected; }
17
18Signed_128 signed_round_trip (Signed_128 value) { return value; }
19Unsigned_128 unsigned_round_trip (Unsigned_128 value) { return value; }
20
21int signed_matches (Signed_128 value) { return value == signed_expected; }
22int unsigned_matches (Unsigned_128 value) { return value == unsigned_expected; }
23

Tests.

Before the patch
GNAT rejects the generated specification because uu_int128_unsigned is undefined.
After the patch
Signed and unsigned 128-bit values round-trip by value through Ada and C++ at -O0 and -O2.
int128-types.C C++ · 22 lines 
/* { dg-do compile } */
/* { dg-options "-fdump-ada-spec-slim" } */
/* { dg-final { scan-file int128_types_c.ads "subtype Signed_128 is Extensions.Signed_128" } } */
/* { dg-final { scan-file int128_types_c.ads "subtype Unsigned_128 is Extensions.Unsigned_128" } } */

using Signed_128 = __int128;
using Unsigned_128 = unsigned __int128;

static const Signed_128 signed_expected
  = -((static_cast<Signed_128> (1) << 100) + 12345);
static const Unsigned_128 unsigned_expected
  = (static_cast<Unsigned_128> (1) << 127)
    | (static_cast<Unsigned_128> (1) << 80) | 67890;

Signed_128 signed_seed () { return signed_expected; }
Unsigned_128 unsigned_seed () { return unsigned_expected; }

Signed_128 signed_round_trip (Signed_128 value) { return value; }
Unsigned_128 unsigned_round_trip (Unsigned_128 value) { return value; }

int signed_matches (Signed_128 value) { return value == signed_expected; }
int unsigned_matches (Unsigned_128 value) { return value == unsigned_expected; }

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int128_types_consumer.adb Ada · 15 lines 
with Interfaces.C;
with Int128_Types_C;

procedure Int128_Types_Consumer is
   use type Interfaces.C.int;
   use Int128_Types_C;
begin
   if signed_matches (signed_round_trip (signed_seed)) /= 1 then
      raise Program_Error with "signed __int128 round trip failed";
   end if;

   if unsigned_matches (unsigned_round_trip (unsigned_seed)) /= 1 then
      raise Program_Error with "unsigned __int128 round trip failed";
   end if;
end Int128_Types_Consumer;

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run-test.sh shell · 78 lines 
#!/usr/bin/env bash
set -euo pipefail

if [[ $# -ne 3 ]]; then
  echo "usage: $0 TOOLCHAIN_ROOT GCC_VERSION unpatched|patched" >&2
  exit 2
fi

root=$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)
source "$root/scripts/regression-common.sh"
resolve_regression_toolchain "$1"
version=$2
major=${version%%.*}
state=$3
[[ "$state" == unpatched || "$state" == patched ]] || {
  echo "error: state must be unpatched or patched" >&2
  exit 2
}

gxx="$REGRESSION_TOOLCHAIN/bin/g++"
[[ -x "$gxx" ]] || {
  echo "error: no g++ in $REGRESSION_TOOLCHAIN" >&2
  exit 1
}

cxx_fixture="$root/bundles/cxx-ada-int128-types/tests/int128-types.C"
ada_fixture="$root/bundles/cxx-ada-int128-types/tests/int128_types_consumer.adb"
work=$(mktemp -d "${TMPDIR:-/tmp}/gnat-cxx-ada-int128-types.XXXXXX")
trap 'rm -rf "$work"' EXIT

for optimization in 0 2; do
  case_dir="$work/O$optimization"
  mkdir -p "$case_dir"
  cp "$cxx_fixture" "$ada_fixture" "$case_dir/"
  (
    cd "$case_dir"
    "${REGRESSION_ENV[@]}" "$gxx" -c "-O$optimization" \
      -fdump-ada-spec-slim int128-types.C
  )

  spec="$case_dir/int128_types_c.ads"
  [[ -f "$spec" ]] || {
    echo "error: g++ did not generate $spec" >&2
    exit 1
  }

  set +e
  (
    cd "$case_dir"
    "${REGRESSION_ENV[@]}" "$REGRESSION_GNATMAKE" -q -f \
      "-O$optimization" int128_types_consumer.adb \
      -largs int128-types.o -lstdc++
    "${REGRESSION_ENV[@]}" ./int128_types_consumer
  ) >"$case_dir/run.log" 2>&1
  run_status=$?
  set -e

  if [[ "$state" == unpatched && ( "$major" == 13 || "$major" == 14 ) ]]; then
    [[ $run_status -ne 0 ]] || {
      echo "error: unpatched __int128 regression unexpectedly passed" >&2
      exit 1
    }
    grep -Eiq 'uu_int128_unsigned.*undefined' "$case_dir/run.log" || {
      cat "$case_dir/run.log"
      exit 1
    }
    echo "cxx-ada-int128-types -O$optimization: expected undefined unsigned type (GCC $version)"
    continue
  fi

  [[ $run_status -eq 0 ]] || {
    cat "$case_dir/run.log"
    exit 1
  }
  grep -Eq 'Extensions\.Signed_128' "$spec"
  grep -Eq 'Extensions\.Unsigned_128' "$spec"
  echo "cxx-ada-int128-types -O$optimization: supported (GCC $version, $state)"
done

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Commands.

Apply the patch
patch --fuzz=0 -p1 -i bundles/cxx-ada-int128-types/patches/gcc-13-14.patch
Build the compiler
PATH=/path/to/bootstrap/bin:$PATH ./scripts/build-gnat.sh SOURCE BUILD INSTALL
Run the regression
./scripts/run-regressions.sh INSTALL 1.2.0 GCC_MAJOR patched

Metadata.

Affected releases
  • 13.2.0
  • 14.2.0
Known-good releases
  • 15.3.0
  • 16.1.0
  • 16.2.0
Files modified
  • gcc/c-family/c-ada-spec.cc
  • gcc/testsuite/g++.dg/ada-spec/int128-types.C
Regression tests
  • gcc/testsuite/g++.dg/ada-spec/int128-types.C
Before the patch
GNAT rejects the generated specification because uu_int128_unsigned is undefined.
After the patch
Signed and unsigned 128-bit values round-trip by value through Ada and C++ at -O0 and -O2.
Upstream issue
Pending GCC Bugzilla filing.
Upstream submission
Not yet filed or submitted upstream.
Provenance
Repository-authored backport of the __int128 prefix recognition present in the pinned GCC 15 and 16 sources, with an executable regression; exact application verified locally against the pinned Darwin GCC 13 and 14 identities. Pinned FSF release application is required by Linux CI.
Licensing
GCC-derived compiler hunks remain GPL-3.0-or-later. The new test is proposed for the GCC testsuite under GCC project terms.
Repository fixture
bundles/cxx-ada-int128-types/tests/int128-types.C
Fixture SHA-256
8bce39aa86a2cd371c8f98b5f7e6f7f71bd021e1fefcb0b63666ebcb52ce42e3
Test runner
bundles/cxx-ada-int128-types/run-test.sh