clang-cl: Support the /fp options (PR23112)

[hans]

Summary

This hooks up the /fp options as aliases for -f[no-]fast-math and -f[no]-trapping-math. It probably doesn't match cl.exe's behaviour completely, but hopefully it's close enough.

[majnemer]

LGTM, this is as close as LLVM is going to get to MSVC's behavior.

include/clang/Driver/CLCompatOptions.td

 // already in the right group.)
 
 def _SLASH_C : CLFlag<"C">, HelpText<"Don't discard comments when preprocessing">,
   Alias<C>;
 def _SLASH_c : CLFlag<"c">, HelpText<"Compile only">, Alias<c>;
 def _SLASH_D : CLJoinedOrSeparate<"D">, HelpText<"Define macro">,
   MetaVarName<"<macro[=value]>">, Alias<D>;
 def _SLASH_E : CLFlag<"E">, HelpText<"Preprocess to stdout">, Alias<E>;
+def _SLASH_fp_except : CLFlag<"fp:except">, HelpText<"">, Alias<ftrapping_math>;
+def _SLASH_fp_except_ : CLFlag<"fp:except-">, HelpText<"">, Alias<fno_trapping_math>;
+def _SLASH_fp_fast : CLFlag<"fp:fast">, HelpText<"">, Alias<ffast_math>;
+def _SLASH_fp_precise : CLFlag<"fp:precise">, HelpText<"">, Alias<fno_fast_math>;
+def _SLASH_fp_strict : CLFlag<"fp:strict">, HelpText<"">, Alias<fno_fast_math>;
 def _SLASH_GR : CLFlag<"GR">, HelpText<"Enable emission of RTTI data">;
 def _SLASH_GR_ : CLFlag<"GR-">, HelpText<"Disable emission of RTTI data">;
 def _SLASH_GF_ : CLFlag<"GF-">, HelpText<"Disable string pooling">,
   Alias<fwritable_strings>;
 def _SLASH_Gs : CLJoined<"Gs">, HelpText<"Set stack probe size">,
   Alias<mstack_probe_size>;
 def _SLASH_Gy : CLFlag<"Gy">, HelpText<"Put each function in its own section">,
   Alias<ffunction_sections>;

 def _SLASH_bigobj : CLFlag<"bigobj">;
 def _SLASH_clr : CLJoined<"clr">;
 def _SLASH_doc : CLJoined<"doc">;
 def _SLASH_FA_joined : CLJoined<"FA">;
 def _SLASH_favor : CLJoined<"favor">;
 def _SLASH_FC : CLFlag<"FC">;
 def _SLASH_F : CLFlag<"F">;
 def _SLASH_Fm : CLJoined<"Fm">;
-def _SLASH_fp : CLJoined<"fp">;
 def _SLASH_Fp : CLJoined<"Fp">;
 def _SLASH_Fr : CLJoined<"Fr">;
 def _SLASH_FR : CLJoined<"FR">;
 def _SLASH_FU : CLJoinedOrSeparate<"FU">;
 def _SLASH_Fx : CLFlag<"Fx">;
 def _SLASH_G1 : CLFlag<"G1">;
 def _SLASH_G2 : CLFlag<"G2">;
 def _SLASH_GA : CLFlag<"GA">;

test/Driver/cl-options.c

 // E: "-E"
 // E: "-o" "-"
 
 // RUN: %clang_cl /EP -### -- %s 2>&1 | FileCheck -check-prefix=EP %s
 // EP: "-E"
 // EP: "-P"
 // EP: "-o" "-"
 
+// RUN: %clang_cl /fp:fast /fp:except -### -- %s 2>&1 | FileCheck -check-prefix=fpexcept %s
+// fpexcept-NOT: -menable-unsafe-fp-math
+
+// RUN: %clang_cl /fp:fast /fp:except /fp:except- -### -- %s 2>&1 | FileCheck -check-prefix=fpexcept_ %s
+// fpexcept_: -menable-unsafe-fp-math
+
+// RUN: %clang_cl /fp:precise /fp:fast -### -- %s 2>&1 | FileCheck -check-prefix=fpfast %s
+// fpfast: -menable-unsafe-fp-math
+// fpfast: -ffast-math
+
+// RUN: %clang_cl /fp:fast /fp:precise -### -- %s 2>&1 | FileCheck -check-prefix=fpprecise %s
+// fpprecise-NOT: -menable-unsafe-fp-math
+// fpprecise-NOT: -ffast-math
+
+// RUN: %clang_cl /fp:fast /fp:strict -### -- %s 2>&1 | FileCheck -check-prefix=fpstrict %s
+// fpstrict-NOT: -menable-unsafe-fp-math
+// fpstrict-NOT: -ffast-math
+
 // RTTI is on by default; just check that we don't error.
 // RUN: %clang_cl /Zs /GR -- %s 2>&1
 
 // RUN: %clang_cl /GR- -### -- %s 2>&1 | FileCheck -check-prefix=GR_ %s
 // GR_: -fno-rtti
 
 // RUN: %clang_cl /Gy -### -- %s 2>&1 | FileCheck -check-prefix=Gy %s
 // Gy: -ffunction-sections

 // RUN:     /Fafilename \
 // RUN:     /FAs \
 // RUN:     /FAu \
 // RUN:     /favor:blend \
 // RUN:     /FC \
 // RUN:     /Fifoo \
 // RUN:     /Fmfoo \
 // RUN:     /FpDebug\main.pch \
-// RUN:     /fp:precise \
 // RUN:     /Frfoo \
 // RUN:     /FRfoo \
 // RUN:     /FU foo \
 // RUN:     /Fx \
 // RUN:     /G1 \
 // RUN:     /G2 \
 // RUN:     /GA \
 // RUN:     /Gd \