Compiler warning flags

There are some differences in how NVIDIA's nvcc and the SCALE compiler in "nvcc mode" interpret compiler flags.

clang++ flags

The SCALE compiler accepts all of clang++'s usual flags in addition to those provided by nvcc, except where doing so would create an ambiguity.

Compiler warnings

The SCALE compiler has the same default warning behaviour as clang, which is somewhat more strict than nvcc. Warnings may be disabled with the usual -Wno- flags documented in the clang diagnostics reference.

There may be value in enabling even more warnings to find further issues and improve your code.

Note that the end of every compiler warning message tells you the name of the warning flag it is associated with, such as:

warning: implicit conversion from 'int' to 'float' changes value from 
2147483647 to 2147483648 [-Wimplicit-const-int-float-conversion]

By changing -W to -Wno-, you obtain the flag required to disable that warning.

The SCALE implementation of the CUDA runtime/driver APIs uses [[nodiscard]] for the error return codes, meaning you'll get a warning from code that ignores potential errors from CUDA APIs. This warning can be disabled via -Wno-unused-result.

-Werror

nvcc's -Werror takes an argument specifying the types of warnings that should be errors, such as:

-Werror reorder,default-stream-launch

This differs from clang's syntax, which consists of either a lone -Werror to make all warnings into errors, or a set of -Werror=name flags to make specific things into errors.

In nvcc mode, the SCALE compiler accepts only the nvcc syntax, but allows the same set of diagnostic names accepted by clang (as well as the special names supported by NVIDIA's nvcc). For example:

nvcc -Werror=documentation,implicit-int-conversion foo.cu
clang++ -Werror=documentation -Werror=implicit-int-conversion foo.cu

Since SCALE enables more warnings than nvcc does by default, many projects using -Werror with nvcc will not compile without either disabling the flag or fixing the underlying code issues.