[CLANG][PATCH][FPEnv] Add support for option -ffp-eval-method and extend #pragma float_control similarly

The Intel compiler ICC supports the option "-fp-model=(source|double|extended)"
which causes the compiler to use a wider type for intermediate floating point
calculations. Also supported is a way to embed this effect in the source
program with #pragma float_control(source|double|extended).
This patch extends pragma float_control syntax, and also adds support
for a new floating point option "-ffp-eval-method=(source|double|extended)".
source: intermediate results use source precision
double: intermediate results use double precision
extended: intermediate results use extended precision

Reviewed By: Aaron Ballman

Differential Revision: https://reviews.llvm.org/D93769

Author: Melanie Blower

clang/docs/LanguageExtensions.rst

@@ -3554,7 +3554,7 @@ specification, a stack is supported so that the ``pragma float_control``
 settings can be pushed or popped.
 
 When ``pragma float_control(precise, on)`` is enabled, the section of code
-governed by the pragma uses precise floating point semantics, effectively
+governed by the pragma uses precise floating-point semantics, effectively
 ``-ffast-math`` is disabled and ``-ffp-contract=on``
 (fused multiply add) is enabled.
 
@@ -3565,8 +3565,29 @@ when ``pragma float_control(precise, off)`` is enabled, the section of code
 governed by the pragma behaves as though the command-line option
 ``-ffp-exception-behavior=ignore`` is enabled.
 
+When ``pragma float_control(source, on)`` is enabled, the section of code governed
+by the pragma behaves as though the command-line option
+``-ffp-eval-method=source`` is enabled. Note: The default
+floating-point evaluation method is target-specific, typically ``source``.
+
+When ``pragma float_control(double, on)`` is enabled, the section of code governed
+by the pragma behaves as though the command-line option
+``-ffp-eval-method=double`` is enabled.
+
+When ``pragma float_control(extended, on)`` is enabled, the section of code governed
+by the pragma behaves as though the command-line option
+``-ffp-eval-method=extended`` is enabled.
+
+When ``pragma float_control(source, off)`` or
+``pragma float_control(double, off)`` or
+``pragma float_control(extended, off)`` is enabled,
+the section of code governed
+by the pragma behaves as though the command-line option
+``-ffp-eval-method=source`` is enabled, returning floating-point evaluation
+method to the default setting.
+
 The full syntax this pragma supports is
-``float_control(except|precise, on|off [, push])`` and
+``float_control(except|precise|source|double|extended, on|off [, push])`` and
 ``float_control(push|pop)``.
 The ``push`` and ``pop`` forms, including using ``push`` as the optional
 third argument, can only occur at file scope.

clang/docs/UsersManual.rst

@@ -1520,6 +1520,17 @@ Note that floating-point operations performed as part of constant initialization
    * ``maytrap`` The compiler avoids transformations that may raise exceptions that would not have been raised by the original code. Constant folding performed by the compiler is exempt from this option.
    * ``strict`` The compiler ensures that all transformations strictly preserve the floating point exception semantics of the original code.
 
+.. option:: -ffp-eval-method=<value>
+
+   Specify the floating-point evaluation method.
+
+   Valid values are: ``source``, ``double``, and ``extended``.
+   The default value is target-specific, typically ``source``.  Details:
+
+   * ``source`` The compiler uses the floating-point type declared in the source program as the evaluation method.
+   * ``double`` The compiler uses ``double`` as the floating-point evaluation method for all float expressions of type that is narrower than ``double``.
+   * ``extended`` The compiler uses ``long double`` as the floating-point evaluation method for all float expressions of type that is narrower than ``long double``.
+
 .. option:: -f[no-]protect-parens:
 
    This option pertains to floating-point types, complex types with

clang/include/clang/Basic/FPOptions.def

@@ -23,4 +23,5 @@ OPTION(NoHonorInfs, bool, 1, NoHonorNaNs)
 OPTION(NoSignedZero, bool, 1, NoHonorInfs)
 OPTION(AllowReciprocal, bool, 1, NoSignedZero)
 OPTION(AllowApproxFunc, bool, 1, AllowReciprocal)
+OPTION(FPEvalMethod, LangOptions::FPEvalMethodKind, 2, AllowApproxFunc)
 #undef OPTION

clang/include/clang/Basic/LangOptions.def

@@ -296,6 +296,7 @@ BENIGN_ENUM_LANGOPT(DefaultFPContractMode, FPModeKind, 2, FPM_Off, "FP contracti
 COMPATIBLE_LANGOPT(ExpStrictFP, 1, false, "Enable experimental strict floating point")
 BENIGN_ENUM_LANGOPT(FPRoundingMode, RoundingMode, 3, RoundingMode::NearestTiesToEven, "FP Rounding Mode type")
 BENIGN_ENUM_LANGOPT(FPExceptionMode, FPExceptionModeKind, 2, FPE_Ignore, "FP Exception Behavior Mode type")
+BENIGN_ENUM_LANGOPT(FPEvalMethod, FPEvalMethodKind, 2, FEM_TargetDefault, "FP type used for floating point arithmetic")
 LANGOPT(NoBitFieldTypeAlign , 1, 0, "bit-field type alignment")
 LANGOPT(HexagonQdsp6Compat , 1, 0, "hexagon-qdsp6 backward compatibility")
 LANGOPT(ObjCAutoRefCount , 1, 0, "Objective-C automated reference counting")

clang/include/clang/Basic/LangOptions.h

@@ -233,6 +233,19 @@ class LangOptions : public LangOptionsBase {
   /// Possible exception handling behavior.
   enum class ExceptionHandlingKind { None, SjLj, WinEH, DwarfCFI, Wasm };
 
+  /// Possible float expression evaluation method choices.
+  enum FPEvalMethodKind {
+    /// Use the declared type for fp arithmetic.
+    FEM_Source,
+    /// Use the type double for fp arithmetic.
+    FEM_Double,
+    /// Use extended type for fp arithmetic.
+    FEM_Extended,
+    /// Use the default float eval method specified by Target:
+    //  most targets are defined with evaluation method FEM_Source.
+    FEM_TargetDefault
+  };
+
   enum class LaxVectorConversionKind {
     /// Permit no implicit vector bitcasts.
     None,
@@ -524,6 +537,7 @@ class FPOptions {
       setAllowFEnvAccess(true);
     else
       setAllowFEnvAccess(LangOptions::FPM_Off);
+    setFPEvalMethod(LO.getFPEvalMethod());
   }
 
   bool allowFPContractWithinStatement() const {

clang/include/clang/Basic/PragmaKinds.h

@@ -32,7 +32,10 @@ enum PragmaFloatControlKind {
   PFC_Except,    // #pragma float_control(except [,on])
   PFC_NoExcept,  // #pragma float_control(except, off)
   PFC_Push,      // #pragma float_control(push)
-  PFC_Pop        // #pragma float_control(pop)
+  PFC_Pop,       // #pragma float_control(pop)
+  PFC_Source,    // #pragma float_control(source, {on|off} [,push])
+  PFC_Double,    // #pragma float_control(double, {on|off} [,push])
+  PFC_Extended,  // #pragma float_control(extended, {on|off} [,push])
 };
 }
 

clang/include/clang/Basic/TargetInfo.h

@@ -687,7 +687,8 @@ class TargetInfo : public virtual TransferrableTargetInfo,
   }
 
   /// Return the value for the C99 FLT_EVAL_METHOD macro.
-  virtual unsigned getFloatEvalMethod() const { return 0; }
+  //  Note: implementation defined values may be negative.
+  virtual int getFPEvalMethod() const { return 0; }
 
   // getLargeArrayMinWidth/Align - Return the minimum array size that is
   // 'large' and its alignment.

clang/include/clang/Driver/Options.td

@@ -1434,6 +1434,11 @@ def : Flag<["-"], "fextended-identifiers">, Group<clang_ignored_f_Group>;
 def : Flag<["-"], "fno-extended-identifiers">, Group<f_Group>, Flags<[Unsupported]>;
 def fhosted : Flag<["-"], "fhosted">, Group<f_Group>;
 def fdenormal_fp_math_EQ : Joined<["-"], "fdenormal-fp-math=">, Group<f_Group>, Flags<[CC1Option]>;
+def ffp_eval_method_EQ : Joined<["-"], "ffp-eval-method=">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Specifies the evaluation method to use for floating-point arithmetic.">,
+  Values<"source,double,extended">, NormalizedValuesScope<"LangOptions">,
+  NormalizedValues<["FEM_Source", "FEM_Double", "FEM_Extended"]>,
+  MarshallingInfoEnum<LangOpts<"FPEvalMethod">, "FEM_TargetDefault">;
 def ffp_model_EQ : Joined<["-"], "ffp-model=">, Group<f_Group>, Flags<[NoXarchOption]>,
   HelpText<"Controls the semantics of floating-point calculations.">;
 def ffp_exception_behavior_EQ : Joined<["-"], "ffp-exception-behavior=">, Group<f_Group>, Flags<[CC1Option]>,

clang/include/clang/Lex/Preprocessor.h

@@ -178,12 +178,17 @@ class Preprocessor {
   IdentifierInfo *Ident__is_target_vendor;         // __is_target_vendor
   IdentifierInfo *Ident__is_target_os;             // __is_target_os
   IdentifierInfo *Ident__is_target_environment;    // __is_target_environment
+  IdentifierInfo *Ident__FLT_EVAL_METHOD__ = nullptr; // __FLT_EVAL_METHOD__
 
   // Weak, only valid (and set) while InMacroArgs is true.
   Token* ArgMacro;
 
   SourceLocation DATELoc, TIMELoc;
 
+  // Corresponding to __FLT_EVAL_METHOD__. Initialized from TargetInfo
+  // or the command line. Implementation-defined values can be negative.
+  int CurrentFPEvalMethod = 0;
+
   // Next __COUNTER__ value, starts at 0.
   unsigned CounterValue = 0;
 
@@ -1988,6 +1993,8 @@ class Preprocessor {
   }
   unsigned getCounterValue() const { return CounterValue; }
   void setCounterValue(unsigned V) { CounterValue = V; }
+  int getCurrentFPEvalMethod() const { return CurrentFPEvalMethod; }
+  void setCurrentFPEvalMethod(int V) { CurrentFPEvalMethod = V; }
 
   /// Retrieves the module that we're currently building, if any.
   Module *getCurrentModule();

clang/include/clang/Lex/PreprocessorOptions.h

@@ -146,6 +146,9 @@ class PreprocessorOptions {
   /// When enabled, the preprocessor will construct editor placeholder tokens.
   bool LexEditorPlaceholders = true;
 
+  /// When enabled, the preprocessor will expand special builtin macros.
+  bool LexExpandSpecialBuiltins = true;
+
   /// True if the SourceManager should report the original file name for
   /// contents of files that were remapped to other files. Defaults to true.
   bool RemappedFilesKeepOriginalName = true;
@@ -249,6 +252,7 @@ class PreprocessorOptions {
     ImplicitPCHInclude.clear();
     SingleFileParseMode = false;
     LexEditorPlaceholders = true;
+    LexExpandSpecialBuiltins = true;
     RetainRemappedFileBuffers = true;
     PrecompiledPreambleBytes.first = 0;
     PrecompiledPreambleBytes.second = false;

clang/include/clang/Sema/Sema.h

@@ -1502,19 +1502,15 @@ class Sema final {
   /// statements.
   class FPFeaturesStateRAII {
   public:
-    FPFeaturesStateRAII(Sema &S) : S(S), OldFPFeaturesState(S.CurFPFeatures) {
-      OldOverrides = S.FpPragmaStack.CurrentValue;
-    }
-    ~FPFeaturesStateRAII() {
-      S.CurFPFeatures = OldFPFeaturesState;
-      S.FpPragmaStack.CurrentValue = OldOverrides;
-    }
+    FPFeaturesStateRAII(Sema &S);
+    ~FPFeaturesStateRAII();
     FPOptionsOverride getOverrides() { return OldOverrides; }
 
   private:
     Sema& S;
     FPOptions OldFPFeaturesState;
     FPOptionsOverride OldOverrides;
+    int OldEvalMethod;
   };
 
   void addImplicitTypedef(StringRef Name, QualType T);

clang/lib/Basic/Targets/OSTargets.h

@@ -735,7 +735,7 @@ class AIXTargetInfo : public OSTargetInfo<Target> {
   }
 
   // AIX sets FLT_EVAL_METHOD to be 1.
-  unsigned getFloatEvalMethod() const override { return 1; }
+  int getFPEvalMethod() const override { return 1; }
   bool hasInt128Type() const override { return false; }
 
   bool defaultsToAIXPowerAlignment() const override { return true; }

clang/lib/Basic/Targets/X86.h

@@ -165,7 +165,7 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
     return LongDoubleFormat == &llvm::APFloat::IEEEquad() ? "g" : "e";
   }
 
-  unsigned getFloatEvalMethod() const override {
+  int getFPEvalMethod() const override {
     // X87 evaluates with 80 bits "long double" precision.
     return SSELevel == NoSSE ? 2 : 0;
   }
@@ -468,12 +468,12 @@ class LLVM_LIBRARY_VISIBILITY NetBSDI386TargetInfo
   NetBSDI386TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : NetBSDTargetInfo<X86_32TargetInfo>(Triple, Opts) {}
 
-  unsigned getFloatEvalMethod() const override {
+  int getFPEvalMethod() const override {
     unsigned Major, Minor, Micro;
     getTriple().getOSVersion(Major, Minor, Micro);
     // New NetBSD uses the default rounding mode.
     if (Major >= 7 || (Major == 6 && Minor == 99 && Micro >= 26) || Major == 0)
-      return X86_32TargetInfo::getFloatEvalMethod();
+      return X86_32TargetInfo::getFPEvalMethod();
     // NetBSD before 6.99.26 defaults to "double" rounding.
     return 1;
   }

clang/lib/Driver/ToolChains/Clang.cpp

@@ -2631,6 +2631,8 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
   StringRef FPModel = "";
   // -ffp-exception-behavior options: strict, maytrap, ignore
   StringRef FPExceptionBehavior = "";
+  // -ffp-eval-method options: double, extended, source
+  StringRef FPEvalMethod = "";
   const llvm::DenormalMode DefaultDenormalFPMath =
       TC.getDefaultDenormalModeForType(Args, JA);
   const llvm::DenormalMode DefaultDenormalFP32Math =
@@ -2822,6 +2824,18 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       break;
     }
 
+    // Validate and pass through -ffp-eval-method option.
+    case options::OPT_ffp_eval_method_EQ: {
+      StringRef Val = A->getValue();
+      if (Val.equals("double") || Val.equals("extended") ||
+          Val.equals("source"))
+        FPEvalMethod = Val;
+      else
+        D.Diag(diag::err_drv_unsupported_option_argument)
+            << A->getOption().getName() << Val;
+      break;
+    }
+
     case options::OPT_ffinite_math_only:
       HonorINFs = false;
       HonorNaNs = false;
@@ -2965,6 +2979,9 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
     CmdArgs.push_back(Args.MakeArgString("-ffp-exception-behavior=" +
                       FPExceptionBehavior));
 
+  if (!FPEvalMethod.empty())
+    CmdArgs.push_back(Args.MakeArgString("-ffp-eval-method=" + FPEvalMethod));
+
   ParseMRecip(D, Args, CmdArgs);
 
   // -ffast-math enables the __FAST_MATH__ preprocessor macro, but check for the

clang/lib/Frontend/CompilerInvocation.cpp

@@ -4242,8 +4242,13 @@ static bool ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
   // Always avoid lexing editor placeholders when we're just running the
   // preprocessor as we never want to emit the
   // "editor placeholder in source file" error in PP only mode.
-  if (isStrictlyPreprocessorAction(Action))
+  // Certain predefined macros which depend upon semantic processing,
+  // for example __FLT_EVAL_METHOD__, are not expanded in PP mode, they
+  // appear in the preprocessed output as an unexpanded macro name.
+  if (isStrictlyPreprocessorAction(Action)) {
     Opts.LexEditorPlaceholders = false;
+    Opts.LexExpandSpecialBuiltins = false;
+  }
 
   return Diags.getNumErrors() == NumErrorsBefore;
 }

clang/lib/Frontend/InitPreprocessor.cpp

@@ -1077,7 +1077,8 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   }
 
   // Macros to control C99 numerics and <float.h>
-  Builder.defineMacro("__FLT_EVAL_METHOD__", Twine(TI.getFloatEvalMethod()));
+  // Note: __FLT_EVAL_METHOD__ is not defined here since it is a special
+  // builtin macro, its value may fluctuate during compilation.
   Builder.defineMacro("__FLT_RADIX__", "2");
   Builder.defineMacro("__DECIMAL_DIG__", "__LDBL_DECIMAL_DIG__");
 

clang/lib/Lex/PPMacroExpansion.cpp

@@ -345,6 +345,11 @@ void Preprocessor::RegisterBuiltinMacros() {
   Ident__TIME__ = RegisterBuiltinMacro(*this, "__TIME__");
   Ident__COUNTER__ = RegisterBuiltinMacro(*this, "__COUNTER__");
   Ident_Pragma  = RegisterBuiltinMacro(*this, "_Pragma");
+  if (PPOpts->LexExpandSpecialBuiltins)
+    // Suppress macro expansion if compiler stops before semantic analysis,
+    // the macro identifier will appear in the preprocessed output.
+    Ident__FLT_EVAL_METHOD__ =
+        RegisterBuiltinMacro(*this, "__FLT_EVAL_METHOD__");
 
   // C++ Standing Document Extensions.
   if (getLangOpts().CPlusPlus)
@@ -1607,6 +1612,10 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
     // Surround the string with " and strip the trailing newline.
     OS << '"' << StringRef(Result).drop_back() << '"';
     Tok.setKind(tok::string_literal);
+  } else if (II == Ident__FLT_EVAL_METHOD__) {
+    // __FLT_EVAL_METHOD__ expands to a simple numeric value.
+    OS << getCurrentFPEvalMethod();
+    Tok.setKind(tok::numeric_constant);
   } else if (II == Ident__COUNTER__) {
     // __COUNTER__ expands to a simple numeric value.
     OS << CounterValue++;
@@ -1704,8 +1713,7 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
 
         return false;
       });
-  } else if (II == Ident__has_cpp_attribute ||
-             II == Ident__has_c_attribute) {
+  } else if (II == Ident__has_cpp_attribute || II == Ident__has_c_attribute) {
     bool IsCXX = II == Ident__has_cpp_attribute;
     EvaluateFeatureLikeBuiltinMacro(
         OS, Tok, II, *this, [&](Token &Tok, bool &HasLexedNextToken) -> int {
@@ -1732,8 +1740,7 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
                                    getLangOpts())
                     : 0;
         });
-  } else if (II == Ident__has_include ||
-             II == Ident__has_include_next) {
+  } else if (II == Ident__has_include || II == Ident__has_include_next) {
     // The argument to these two builtins should be a parenthesized
     // file name string literal using angle brackets (<>) or
     // double-quotes ("").