flang 15 fails to build on i386 with error: non-constant-expression cannot be narrowed from type 'long long' to 'std::size_t' (aka 'unsigned int') in initializer list [-Wc++11-narrowing]

[sylvestre]

On Debian unstable:

/<<PKGBUILDDIR>>/build-llvm/./bin/clang++ -DFLANG_LITTLE_ENDIAN=1 -DFLANG_VENDOR="\"Debian \"" -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE -D_LARGEFILE_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/<<PKGBUILDDIR>>/build-llvm/tools/clang/stage2-bins/tools/flang/lib/Evaluate -I/<<PKGBUILDDIR>>/flang/lib/Evaluate -I/<<PKGBUILDDIR>>/flang/include -I/<<PKGBUILDDIR>>/build-llvm/tools/clang/stage2-bins/tools/flang/include -I/<<PKGBUILDDIR>>/build-llvm/tools/clang/stage2-bins/include -I/<<PKGBUILDDIR>>/llvm/include -isystem /<<PKGBUILDDIR>>/llvm/../mlir/include -isystem /<<PKGBUILDDIR>>/build-llvm/tools/clang/stage2-bins/tools/mlir/include -isystem /<<PKGBUILDDIR>>/build-llvm/tools/clang/stage2-bins/tools/clang/include -isystem /<<PKGBUILDDIR>>/llvm/../clang/include -fstack-protector-strong -Wformat -Werror=format-security -Wno-unused-command-line-argument -Wdate-time -D_FORTIFY_SOURCE=2 -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -ffile-prefix-map=/<<PKGBUILDDIR>>/build-llvm/tools/clang/stage2-bins=build-llvm/tools/clang/stage2-bins -ffile-prefix-map=/<<PKGBUILDDIR>>/= -no-canonical-prefixes -Wno-deprecated-copy -Wno-string-conversion -Wno-unused-command-line-argument -Wstring-conversion           -Wcovered-switch-default -Wno-nested-anon-types -O3 -DNDEBUG  -fno-exceptions -std=c++17 -MD -MT tools/flang/lib/Evaluate/CMakeFiles/obj.FortranEvaluate.dir/constant.cpp.o -MF tools/flang/lib/Evaluate/CMakeFiles/obj.FortranEvaluate.dir/constant.cpp.o.d -o tools/flang/lib/Evaluate/CMakeFiles/obj.FortranEvaluate.dir/constant.cpp.o -c /<<PKGBUILDDIR>>/flang/lib/Evaluate/constant.cpp
/<<PKGBUILDDIR>>/flang/lib/Evaluate/constant.cpp:296:30: error: non-constant-expression cannot be narrowed from type 'long long' to 'std::size_t' (aka 'unsigned int') in initializer list [-Wc++11-narrowing]
    std::size_t elementBytes{length_ * sizeof(decltype(values_[0]))};
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/<<PKGBUILDDIR>>/flang/lib/Evaluate/constant.cpp:367:1: note: in instantiation of member function 'Fortran::evaluate::Constant<Fortran::evaluate::Type<TypeCategory::Character, 1>>::CopyFrom' requested here
INSTANTIATE_CONSTANT_TEMPLATES
^
/<<PKGBUILDDIR>>/flang/include/flang/Evaluate/constant.h:239:42: note: expanded from macro 'INSTANTIATE_CONSTANT_TEMPLATES'
  FOR_EACH_INTRINSIC_KIND(template class Constant, )
                                         ^
/<<PKGBUILDDIR>>/flang/lib/Evaluate/constant.cpp:296:30: note: insert an explicit cast to silence this issue
    std::size_t elementBytes{length_ * sizeof(decltype(values_[0]))};
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                             static_cast<size_t>(                  )

[kiranchandramohan]

Flang is not supported on 32-bit machines.

[sylvestre]

@kiranchandramohan ok, is that documented somewhere? thanks

[kiranchandramohan]

@sylvestre Flang is not yet ready for users to try out. It is still a Work in Progress. So we have not documented this. The section (https://github.com/llvm/llvm-project/tree/main/flang#supported-c-compilers) lists the supported compilers and the platforms listed there are all 64 bit.
Would you like this to be documented somewhere? If so, do you have a suggestion on where it should be?

[sylvestre]

@kiranchandramohan I proposed this: https://reviews.llvm.org/D141126

also, cmake should refuse to built flang on 32 bits CPU. OK if i propose a patch to implement this?
thanks

[kiranchandramohan]

This might need a discussion, could you post in flang discourse or create a patch and I can add reviewers?

[sylvestre]

for the cmake thing:
https://reviews.llvm.org/D141132