Revert "Currently the control of the eval-method is mixed with fast-math."

Setting __FLT_EVAL_METHOD__ to -1 with fast-math will set
__GLIBC_FLT_EVAL_METHOD to 2 and long double ends up being used for
float_t and double_t. This creates some ABI breakage with various C libraries.
See details here: llvm/llvm-project#60781

This reverts commit bbf0d19.

Author: zahiraam

clang/include/clang/Lex/Preprocessor.h

@@ -193,11 +193,6 @@ class Preprocessor {
   LangOptions::FPEvalMethodKind CurrentFPEvalMethod =
       LangOptions::FPEvalMethodKind::FEM_UnsetOnCommandLine;
 
-  // Keeps the value of the last evaluation method before a
-  // `pragma float_control (precise,off) is applied.
-  LangOptions::FPEvalMethodKind LastFPEvalMethod =
-      LangOptions::FPEvalMethodKind::FEM_UnsetOnCommandLine;
-
   // The most recent pragma location where the floating point evaluation
   // method was modified. This is used to determine whether the
   // 'pragma clang fp eval_method' was used whithin the current scope.
@@ -2335,14 +2330,6 @@ class Preprocessor {
     return LastFPEvalPragmaLocation;
   }
 
-  LangOptions::FPEvalMethodKind getLastFPEvalMethod() const {
-    return LastFPEvalMethod;
-  }
-
-  void setLastFPEvalMethod(LangOptions::FPEvalMethodKind Val) {
-    LastFPEvalMethod = Val;
-  }
-
   void setCurrentFPEvalMethod(SourceLocation PragmaLoc,
                               LangOptions::FPEvalMethodKind Val) {
     assert(Val != LangOptions::FEM_UnsetOnCommandLine &&

clang/lib/Lex/PPMacroExpansion.cpp

@@ -1637,35 +1637,14 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
     Tok.setKind(tok::string_literal);
   } else if (II == Ident__FLT_EVAL_METHOD__) {
     // __FLT_EVAL_METHOD__ is set to the default value.
-    if (getTUFPEvalMethod() ==
-        LangOptions::FPEvalMethodKind::FEM_Indeterminable) {
-      // This is possible if `AllowFPReassoc` or `AllowReciprocal` is enabled.
-      // These modes can be triggered via the command line option `-ffast-math`
-      // or via a `pragam float_control`.
-      // __FLT_EVAL_METHOD__ expands to -1.
-      // The `minus` operator is the next token we read from the stream.
-      auto Toks = std::make_unique<Token[]>(1);
-      OS << "-";
-      Tok.setKind(tok::minus);
-      // Push the token `1` to the stream.
-      Token NumberToken;
-      NumberToken.startToken();
-      NumberToken.setKind(tok::numeric_constant);
-      NumberToken.setLiteralData("1");
-      NumberToken.setLength(1);
-      Toks[0] = NumberToken;
-      EnterTokenStream(std::move(Toks), 1, /*DisableMacroExpansion*/ false,
-                       /*IsReinject*/ false);
-    } else {
-      OS << getTUFPEvalMethod();
-      // __FLT_EVAL_METHOD__ expands to a simple numeric value.
-      Tok.setKind(tok::numeric_constant);
-      if (getLastFPEvalPragmaLocation().isValid()) {
-        // The program is ill-formed. The value of __FLT_EVAL_METHOD__ is
-        // altered by the pragma.
-        Diag(Tok, diag::err_illegal_use_of_flt_eval_macro);
-        Diag(getLastFPEvalPragmaLocation(), diag::note_pragma_entered_here);
-      }
+    OS << getTUFPEvalMethod();
+    // __FLT_EVAL_METHOD__ expands to a simple numeric value.
+    Tok.setKind(tok::numeric_constant);
+    if (getLastFPEvalPragmaLocation().isValid()) {
+      // The program is ill-formed. The value of __FLT_EVAL_METHOD__ is altered
+      // by the pragma.
+      Diag(Tok, diag::err_illegal_use_of_flt_eval_macro);
+      Diag(getLastFPEvalPragmaLocation(), diag::note_pragma_entered_here);
     }
   } else if (II == Ident__COUNTER__) {
     // __COUNTER__ expands to a simple numeric value.

clang/lib/Lex/Preprocessor.cpp

@@ -207,11 +207,6 @@ void Preprocessor::Initialize(const TargetInfo &Target,
   else
     // Set initial value of __FLT_EVAL_METHOD__ from the command line.
     setCurrentFPEvalMethod(SourceLocation(), getLangOpts().getFPEvalMethod());
-  // When `-ffast-math` option is enabled, it triggers several driver math
-  // options to be enabled. Among those, only one the following two modes
-  // affect the eval-method:  reciprocal or reassociate.
-  if (getLangOpts().AllowFPReassoc || getLangOpts().AllowRecip)
-    setCurrentFPEvalMethod(SourceLocation(), LangOptions::FEM_Indeterminable);
 }
 
 void Preprocessor::InitializeForModelFile() {

clang/lib/Sema/SemaAttr.cpp

@@ -565,13 +565,6 @@ void Sema::ActOnPragmaFloatControl(SourceLocation Loc,
   case PFC_Precise:
     NewFPFeatures.setFPPreciseEnabled(true);
     FpPragmaStack.Act(Loc, Action, StringRef(), NewFPFeatures);
-    if (PP.getCurrentFPEvalMethod() ==
-            LangOptions::FPEvalMethodKind::FEM_Indeterminable &&
-        PP.getLastFPEvalPragmaLocation().isValid())
-      // A preceding `pragma float_control(precise,off)` has changed
-      // the value of the evaluation method.
-      // Set it back to its old value.
-      PP.setCurrentFPEvalMethod(SourceLocation(), PP.getLastFPEvalMethod());
     break;
   case PFC_NoPrecise:
     if (CurFPFeatures.getExceptionMode() == LangOptions::FPE_Strict)
@@ -581,10 +574,6 @@ void Sema::ActOnPragmaFloatControl(SourceLocation Loc,
     else
       NewFPFeatures.setFPPreciseEnabled(false);
     FpPragmaStack.Act(Loc, Action, StringRef(), NewFPFeatures);
-    PP.setLastFPEvalMethod(PP.getCurrentFPEvalMethod());
-    // `AllowFPReassoc` or `AllowReciprocal` option is enabled.
-    PP.setCurrentFPEvalMethod(
-        Loc, LangOptions::FPEvalMethodKind::FEM_Indeterminable);
     break;
   case PFC_Except:
     if (!isPreciseFPEnabled())
@@ -608,12 +597,6 @@ void Sema::ActOnPragmaFloatControl(SourceLocation Loc,
     }
     FpPragmaStack.Act(Loc, Action, StringRef(), NewFPFeatures);
     NewFPFeatures = FpPragmaStack.CurrentValue;
-    if (CurFPFeatures.getAllowFPReassociate() ||
-        CurFPFeatures.getAllowReciprocal())
-      // Since we are popping the pragma, we don't want to be passing
-      // a location here.
-      PP.setCurrentFPEvalMethod(SourceLocation(),
-                                CurFPFeatures.getFPEvalMethod());
     break;
   }
   CurFPFeatures = NewFPFeatures.applyOverrides(getLangOpts());

clang/test/CodeGen/X86/fexcess-precision.c

@@ -380,7 +380,7 @@ _Float16 f(_Float16 a, _Float16 b, _Float16 c, _Float16 d) {
 //
 // CHECK-UNSAFE-LABEL: @getFEM(
 // CHECK-UNSAFE-NEXT:  entry:
-// CHECK-UNSAFE-NEXT:    ret i32 -1
+// CHECK-UNSAFE-NEXT:    ret i32 0
 //
 int getFEM() {
   return __FLT_EVAL_METHOD__;

clang/test/CodeGen/eval-method-fast-math.cpp

@@ -17,7 +17,7 @@
 // RUN:   %s -o - | FileCheck %s  -strict-whitespace
 
 // RUN: %clang_cc1 -E -dM -triple=x86_64-apple-macos13.0 -ffast-math \
-// RUN:   %s -o - | FileCheck %s -check-prefix=CHECK-MINUS-ONE -strict-whitespace
+// RUN:   %s -o - | FileCheck %s -check-prefix=CHECK -strict-whitespace
 
 // RUN: %clang_cc1 -E -dM -triple i386-pc-windows -target-cpu pentium4 %s -o - \
 // RUN:   | FileCheck %s  -strict-whitespace
@@ -64,7 +64,6 @@
 
 int foo() {
   // CHECK: #define Name "One"
-  // CHECK-MINUS-ONE: #define Name "MinusOne"
   // EXT: #define Name "Three"
   return Name;
 }