hfinkel added a comment. In https://reviews.llvm.org/D53157#1301782, @cameron.mcinally wrote:
> Fair enough. Just for conversation's sake, I was envisioning the FE support a > little differently... > > 1. Add a command line option, say `-ffpe_safe=[true|false]`, that toggles > FPEnv-safe code generation for a whole file. A `-ffpe_safe=true` would be > equivalent to `FENV_ACCESS=ON` at the beginning of a translation unit and we > would capture it in some FE variable. That command line option can be > overridden by the FENV_ACCESS pragma. To bikeshed, I'd prefer we don't have an underscore in the name of the command-line flag. > > > 2. If the FENV_ACCESS pragma is seen, carry a nop/metadata/something > construct to toggle the FE variable during IR generation. > 3. Then when generating IR, choose between constrained/unconstrained IR > depending on the state of the FE variable. > > #1 may seem superfluous, but there are certain benchmarks (e.g. SPEC CPU) > that do not allow for code modifications. So, in order to run those with > FPEnv-safe code, we'd need a non-invasive way to toggle FPEnv-safe code > generation. > > I'll also add that my interpretation of FENV_ACCESS in the C Standard > [7.6.1] implies that we have to track the FENV_ACCESS pragma. That is, it's > not okay to ignore FENV_ACCESS=OFF. When we transfer from FENV_ACCESS=OFF > code to FENV_ACCESS=ON code, the rounding mode needs to be reset to the > default setting. But, I'm open to hearing other interpretations. My copy of > the Standard is old, so please correct me if this changed... > > ``` When execution passes from a part of the program translated with > FENV_ACCESS ‘‘off’’ to a part translated with FENV_ACCESS ‘‘on’’, the state > of the floating-point status flags is unspecified and the floating-point > control modes have their default settings. ``` The rounding mode does need to be reset to its default setting when passing from FENV_ACCESS "on" to FENV_ACCESS "off", but that seems to be the user's responsibility. Are you saying that the implementation should reset it on that transition? https://reviews.llvm.org/D53157 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
