[libc] buildbot is unhappy about `strfroml` with negative NAN on aarch64

[SchrodingerZhu]

The issue is not reproducible on my machine using clang 18.1.x.

LLVM Buildbot has detected a new failure on builder libc-aarch64-ubuntu-fullbuild-dbg running on libc-aarch64-ubuntu while building libc at step 4 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/71/builds/3666

Here is the relevant piece of the build log for the reference:

Step 4 (annotate) failure: 'python ../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py ...' (failure)
...
[2651/3600] Running unit test libc.test.src.math.smoke.roundevenf16_test.__unit__
[==========] Running 3 tests from 1 test suite.
[ RUN      ] LlvmLibcRoundEvenTest.SpecialNumbers
[       OK ] LlvmLibcRoundEvenTest.SpecialNumbers (4 us)
[ RUN      ] LlvmLibcRoundEvenTest.RoundedNubmers
[       OK ] LlvmLibcRoundEvenTest.RoundedNubmers (1 us)
[ RUN      ] LlvmLibcRoundEvenTest.Fractions
[       OK ] LlvmLibcRoundEvenTest.Fractions (3 us)
Ran 3 tests.  PASS: 3  FAIL: 0
[2652/3600] Running unit test libc.test.src.stdlib.strfroml_test.__unit__
FAILED: projects/libc/test/src/stdlib/CMakeFiles/libc.test.src.stdlib.strfroml_test.__unit__ 
cd /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/build/projects/libc/test/src/stdlib && /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/build/projects/libc/test/src/stdlib/libc.test.src.stdlib.strfroml_test.__unit__.__build__
[==========] Running 7 tests from 1 test suite.
[ RUN      ] LlvmLibcStrfromlTest.FloatDecimalFormat
[       OK ] LlvmLibcStrfromlTest.FloatDecimalFormat (112 us)
[ RUN      ] LlvmLibcStrfromlTest.FloatHexExpFormat
[       OK ] LlvmLibcStrfromlTest.FloatHexExpFormat (9 us)
[ RUN      ] LlvmLibcStrfromlTest.FloatDecimalAutoFormat
[       OK ] LlvmLibcStrfromlTest.FloatDecimalAutoFormat (1 us)
[ RUN      ] LlvmLibcStrfromlTest.FloatDecimalExpFormat
[       OK ] LlvmLibcStrfromlTest.FloatDecimalExpFormat (1 us)
[ RUN      ] LlvmLibcStrfromlTest.ImproperFormatString
[       OK ] LlvmLibcStrfromlTest.ImproperFormatString (5 us)
[ RUN      ] LlvmLibcStrfromlTest.InsufficientBufferSize
[       OK ] LlvmLibcStrfromlTest.InsufficientBufferSize (188 us)
[ RUN      ] LlvmLibcStrfromlTest.InfAndNanValues
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:478: FAILURE
      Expected: written
      Which is: 3
To be equal to: static_cast<int>(sizeof("-NAN") - 1)
      Which is: 4
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:478: FAILURE
      Expected: buff
      Which is: NAN
To be equal to: "-NAN"
      Which is: -NAN
[  FAILED  ] LlvmLibcStrfromlTest.InfAndNanValues
Ran 7 tests.  PASS: 6  FAIL: 1
[2653/3600] Running unit test libc.test.src.math.smoke.ceilf_test.__unit__.__NO_ROUND_OPT
[==========] Running 3 tests from 1 test suite.
[ RUN      ] LlvmLibcCeilTest.SpecialNumbers
[       OK ] LlvmLibcCeilTest.SpecialNumbers (3 us)
[ RUN      ] LlvmLibcCeilTest.RoundedNubmers
[       OK ] LlvmLibcCeilTest.RoundedNubmers (2 us)
[ RUN      ] LlvmLibcCeilTest.Fractions
[       OK ] LlvmLibcCeilTest.Fractions (3 us)
Ran 3 tests.  PASS: 3  FAIL: 0
[2654/3600] Running unit test libc.test.src.math.smoke.getpayloadf_test.__unit__
[==========] Running 2 tests from 1 test suite.
Step 8 (libc-unit-tests) failure: libc-unit-tests (failure)
...
[2651/3600] Running unit test libc.test.src.math.smoke.roundevenf16_test.__unit__
[==========] Running 3 tests from 1 test suite.
[ RUN      ] LlvmLibcRoundEvenTest.SpecialNumbers
[       OK ] LlvmLibcRoundEvenTest.SpecialNumbers (4 us)
[ RUN      ] LlvmLibcRoundEvenTest.RoundedNubmers
[       OK ] LlvmLibcRoundEvenTest.RoundedNubmers (1 us)
[ RUN      ] LlvmLibcRoundEvenTest.Fractions
[       OK ] LlvmLibcRoundEvenTest.Fractions (3 us)
Ran 3 tests.  PASS: 3  FAIL: 0
[2652/3600] Running unit test libc.test.src.stdlib.strfroml_test.__unit__
FAILED: projects/libc/test/src/stdlib/CMakeFiles/libc.test.src.stdlib.strfroml_test.__unit__ 
cd /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/build/projects/libc/test/src/stdlib && /home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/build/projects/libc/test/src/stdlib/libc.test.src.stdlib.strfroml_test.__unit__.__build__
[==========] Running 7 tests from 1 test suite.
[ RUN      ] LlvmLibcStrfromlTest.FloatDecimalFormat
[       OK ] LlvmLibcStrfromlTest.FloatDecimalFormat (112 us)
[ RUN      ] LlvmLibcStrfromlTest.FloatHexExpFormat
[       OK ] LlvmLibcStrfromlTest.FloatHexExpFormat (9 us)
[ RUN      ] LlvmLibcStrfromlTest.FloatDecimalAutoFormat
[       OK ] LlvmLibcStrfromlTest.FloatDecimalAutoFormat (1 us)
[ RUN      ] LlvmLibcStrfromlTest.FloatDecimalExpFormat
[       OK ] LlvmLibcStrfromlTest.FloatDecimalExpFormat (1 us)
[ RUN      ] LlvmLibcStrfromlTest.ImproperFormatString
[       OK ] LlvmLibcStrfromlTest.ImproperFormatString (5 us)
[ RUN      ] LlvmLibcStrfromlTest.InsufficientBufferSize
[       OK ] LlvmLibcStrfromlTest.InsufficientBufferSize (188 us)
[ RUN      ] LlvmLibcStrfromlTest.InfAndNanValues
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:478: FAILURE
      Expected: written
      Which is: 3
To be equal to: static_cast<int>(sizeof("-NAN") - 1)
      Which is: 4
/home/libc-buildbot/libc-aarch64-ubuntu/libc-aarch64-ubuntu-fullbuild-dbg/llvm-project/libc/test/src/stdlib/StrfromTest.h:478: FAILURE
      Expected: buff
      Which is: NAN
To be equal to: "-NAN"
      Which is: -NAN
[  FAILED  ] LlvmLibcStrfromlTest.InfAndNanValues
Ran 7 tests.  PASS: 6  FAIL: 1
[2653/3600] Running unit test libc.test.src.math.smoke.ceilf_test.__unit__.__NO_ROUND_OPT
[==========] Running 3 tests from 1 test suite.
[ RUN      ] LlvmLibcCeilTest.SpecialNumbers
[       OK ] LlvmLibcCeilTest.SpecialNumbers (3 us)
[ RUN      ] LlvmLibcCeilTest.RoundedNubmers
[       OK ] LlvmLibcCeilTest.RoundedNubmers (2 us)
[ RUN      ] LlvmLibcCeilTest.Fractions
[       OK ] LlvmLibcCeilTest.Fractions (3 us)
Ran 3 tests.  PASS: 3  FAIL: 0
[2654/3600] Running unit test libc.test.src.math.smoke.getpayloadf_test.__unit__
[==========] Running 2 tests from 1 test suite.

Originally posted by @llvm-ci in #101797 (comment)

[overmighty]

Reproduced it with Clang 11 in Ubuntu container with QEMU:

$ podman run -itv ~/projects/llvm-project/:/root/llvm-project --arch arm64 docker.io/ubuntu:jammy bash

Inside container:

# apt update
# apt ugprade
# apt install g++ clang-11 cmake ninja-build
# cd ~/llvm-project
# cmake -S llvm -B build-aarch64 -G Ninja \
      -DCMAKE_BUILD_TYPE=Debug \
      -DCMAKE_C_COMPILER=clang-11 \
      -DCMAKE_CXX_COMPILER=clang++-11 \
      -DBUILD_SHARED_LIBS=ON \
      -DLLVM_ENABLE_PROJECTS="libc" \
      -DLLVM_OPTIMIZED_TABLEGEN=ON \
      -DLIBC_USE_NEW_HEADER_GEN=OFF
# cmake --build build-aarch64 --target libc.test.src.stdlib.strfroml_test.__unit__

[SchrodingerZhu]

Reproduced with clang-11 on my WSL2 on Surface Pro 11. Error disappears with clang-12.