[clang] [clang][driver] Improve warning message for complex range overrides (PR #154899)

[Shunsuke Watanabe via cfe-commits]

================
@@ -2730,17 +2730,38 @@ static void CollectArgsForIntegratedAssembler(Compilation &C,
   }
 }
 
-static std::string ComplexArithmeticStr(LangOptions::ComplexRangeKind Range) {
-  return (Range == LangOptions::ComplexRangeKind::CX_None)
-             ? ""
-             : "-fcomplex-arithmetic=" + complexRangeKindToStr(Range);
-}
+static void EmitComplexRangeDiag(const Driver &D, StringRef LastOpt,
+                                 LangOptions::ComplexRangeKind Range,
+                                 StringRef NewOpt,
+                                 LangOptions::ComplexRangeKind NewRange) {
+  //  Do not emit a warning if NewOpt overrides LastOpt in the following cases.
+  //
+  // | LastOpt               | NewOpt                |
+  // |-----------------------|-----------------------|
+  // | -fcx-limited-range    | -fno-cx-limited-range |
+  // | -fno-cx-limited-range | -fcx-limited-range    |
+  // | -fcx-fortran-rules    | -fno-cx-fortran-rules |
+  // | -fno-cx-fortran-rules | -fcx-fortran-rules    |
+  // | -ffast-math           | -fno-fast-math        |
+  // | -ffp-model=           | -fno-fast-math        |
+  // | -ffp-model=           | -ffp-model=           |
+  // | -fcomplex-arithmetic= | -fcomplex-arithmetic= |
+  if (LastOpt == NewOpt || NewOpt.empty() || LastOpt.empty() ||
+      (LastOpt == "-fcx-limited-range" && NewOpt == "-fno-cx-limited-range") ||
+      (LastOpt == "-fno-cx-limited-range" && NewOpt == "-fcx-limited-range") ||
+      (LastOpt == "-fcx-fortran-rules" && NewOpt == "-fno-cx-fortran-rules") ||
+      (LastOpt == "-fno-cx-fortran-rules" && NewOpt == "-fcx-fortran-rules") ||
+      (LastOpt == "-ffast-math" && NewOpt == "-fno-fast-math") ||
+      (LastOpt.starts_with("-ffp-model=") && NewOpt == "-fno-fast-math") ||
----------------
s-watanabe314 wrote:

Thank you for the confirmation. I've added only `-ffp-model=xxx -ffast-math` to the list.

>That's what I was a bit worried about; if we start spelling all the cases that don't need a warning we will always miss something ...

I am also concerned about that, but I couldn't think of any better implementation. If we want the simplest implementation that doesn't miss anything, I think the only way is to issue warnings in all cases.

https://github.com/llvm/llvm-project/pull/154899