[PATCH] D72841: Add support for pragma float_control, to control precision and exception behavior at the source level

[Michele Scandale via Phabricator via cfe-commits]

michele.scandale added inline comments.


================
Comment at: clang/include/clang/Basic/LangOptions.h:396-401
+        allow_reassoc(LangOpts.FastMath || LangOpts.AllowFPReassoc),
+        no_nans(LangOpts.FastMath || LangOpts.NoHonorNaNs),
+        no_infs(LangOpts.FastMath || LangOpts.NoHonorInfs),
+        no_signed_zeros(LangOpts.FastMath || LangOpts.NoSignedZero),
+        allow_reciprocal(LangOpts.FastMath || LangOpts.AllowRecip),
+        approx_func(LangOpts.FastMath || LangOpts.ApproxFunc) {}
----------------
Same comment on `LangOpts.FastMath || ` as the one for `CompilerInvocation.cpp`.


================
Comment at: clang/lib/Frontend/CompilerInvocation.cpp:3190-3196
+  Opts.AllowFPReassoc = Opts.FastMath || CGOpts.Reassociate;
+  Opts.NoHonorNaNs =
+      Opts.FastMath || CGOpts.NoNaNsFPMath || Opts.FiniteMathOnly;
+  Opts.NoHonorInfs =
+      Opts.FastMath || CGOpts.NoInfsFPMath || Opts.FiniteMathOnly;
+  Opts.NoSignedZero = Opts.FastMath || CGOpts.NoSignedZeros;
+  Opts.AllowRecip = Opts.FastMath || CGOpts.ReciprocalMath;
----------------
Why do we need `Opts.FastMath || ` here? The code in the compiler driver `clang/lib/Driver/ToolChains/Clang.cpp` (https://github.com/llvm/llvm-project/blob/master/clang/lib/Driver/ToolChains/Clang.cpp#L2510) already takes care of generating the right flags for the CC1 to configure the floating point rules.

Moreover, if we ignore what the compiler driver does, the fact that `Args.hasArg(OPT_ffast_math)` is not considered in the definition of the codegen options such as `NoInfsFPMath`, `NoNaNsFPMath`, `NoSignedZeros`, `Reassociate`, so the you have already two distinct options for the same abstract property that might not match.

I think that at the CC1 level the reasoning should be done in terms of the fine grain options, and let the compiler driver makes life easy for the users -- i.e. `LangOpts.FastMath` should just control whether the macro `__FAST_MATH__` is defined or not.



Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72841/new/

https://reviews.llvm.org/D72841