diff --git a/clang/include/clang/Basic/DiagnosticASTKinds.td b/clang/include/clang/Basic/DiagnosticASTKinds.td
--- a/clang/include/clang/Basic/DiagnosticASTKinds.td
+++ b/clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -72,6 +72,8 @@
   "in a constant expression">;
 def note_constexpr_float_arithmetic : Note<
   "floating point arithmetic produces %select{an infinity|a NaN}0">;
+def note_constexpr_float_arithmetic_strict : Note<
+  "compile time floating point arithmetic suppressed in strict evaluation modes">;
 def note_constexpr_pointer_subtraction_not_same_array : Note<
   "subtracted pointers are not elements of the same array">;
 def note_constexpr_pointer_subtraction_zero_size : Note<
diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -1133,9 +1133,9 @@
 // - #pragma stdc unknown
 def ext_stdc_pragma_ignored : ExtWarn<"unknown pragma in STDC namespace">,
    InGroup<UnknownPragmas>;
-def warn_stdc_fenv_access_not_supported :
-   Warning<"pragma STDC FENV_ACCESS ON is not supported, ignoring pragma">,
-   InGroup<UnknownPragmas>;
+def err_pragma_stdc_fenv_access_scope : Error<
+  "'#pragma STDC FENV_ACCESS' can only appear at file scope or at the start of a "
+  "compound statement">;
 def warn_stdc_fenv_round_not_supported :
    Warning<"pragma STDC FENV_ROUND is not supported">,
    InGroup<UnknownPragmas>;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -4329,6 +4329,7 @@
   void ActOnFinishOfCompoundStmt();
   StmtResult ActOnCompoundStmt(SourceLocation L, SourceLocation R,
                                ArrayRef<Stmt *> Elts, bool isStmtExpr);
+  void ActOnAfterCompoundStatementLeadingPragmas();
 
   /// A RAII object to enter scope of a compound statement.
   class CompoundScopeRAII {
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -2680,6 +2680,12 @@
     Info.CCEDiag(E, diag::note_constexpr_float_arithmetic) << LHS.isNaN();
     return Info.noteUndefinedBehavior();
   }
+  if (const BinaryOperator *BE = dyn_cast<BinaryOperator>(E)) {
+    if (BE->getFPFeaturesInEffect(Info.Ctx.getLangOpts()).isFPConstrained()) {
+      Info.CCEDiag(E, diag::note_constexpr_float_arithmetic_strict);
+      return false;
+    }
+  }
   return true;
 }
 
@@ -13274,6 +13280,10 @@
   case Builtin::BI__builtin_fabsf128:
     if (!EvaluateFloat(E->getArg(0), Result, Info))
       return false;
+    if (E->getFPFeaturesInEffect(Info.Ctx.getLangOpts()).isFPConstrained()) {
+      Info.CCEDiag(E, diag::note_constexpr_float_arithmetic_strict);
+      return false;
+    }
 
     if (Result.isNegative())
       Result.changeSign();
@@ -13325,6 +13335,8 @@
 }
 
 bool FloatExprEvaluator::VisitUnaryOperator(const UnaryOperator *E) {
+  // In C lang ref, the unary - raises no floating point exceptions,
+  // even if the operand is signalling.
   switch (E->getOpcode()) {
   default: return Error(E);
   case UO_Plus:
@@ -13357,6 +13369,11 @@
 bool FloatExprEvaluator::VisitCastExpr(const CastExpr *E) {
   const Expr* SubExpr = E->getSubExpr();
 
+  if (E->getFPFeaturesInEffect(Info.Ctx.getLangOpts()).isFPConstrained()) {
+    // In C lang ref, footnote, cast may raise inexact exception.
+    Info.CCEDiag(E, diag::note_constexpr_float_arithmetic_strict);
+    return false;
+  }
   switch (E->getCastKind()) {
   default:
     return ExprEvaluatorBaseTy::VisitCastExpr(E);
diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -900,8 +900,10 @@
 
   if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
     Builder.setIsFPConstrained(FD->usesFPIntrin());
-    if (FD->usesFPIntrin())
+    if (FD->usesFPIntrin()) {
       Fn->addFnAttr(llvm::Attribute::StrictFP);
+      Builder.setIsFPConstrained(true);
+    }
   }
 
   // If a custom alignment is used, force realigning to this alignment on
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1137,6 +1137,10 @@
   /// definition.
   void SetLLVMFunctionAttributesForDefinition(const Decl *D, llvm::Function *F);
 
+  /// Set the LLVM function attributes that represent floating point
+  /// environment.
+  void setLLVMFunctionFEnvAttributes(const FunctionDecl *D, llvm::Function *F);
+
   /// Return true iff the given type uses 'sret' when used as a return type.
   bool ReturnTypeUsesSRet(const CGFunctionInfo &FI);
 
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1725,6 +1725,15 @@
   }
 }
 
+void CodeGenModule::setLLVMFunctionFEnvAttributes(const FunctionDecl *D,
+                                                  llvm::Function *F) {
+  if (D->usesFPIntrin()) {
+    llvm::AttrBuilder FuncAttrs;
+    FuncAttrs.addAttribute("strictfp");
+    F->addAttributes(llvm::AttributeList::FunctionIndex, FuncAttrs);
+  }
+}
+
 void CodeGenModule::SetCommonAttributes(GlobalDecl GD, llvm::GlobalValue *GV) {
   const Decl *D = GD.getDecl();
   if (dyn_cast_or_null<NamedDecl>(D))
@@ -4554,9 +4563,11 @@
 
   MaybeHandleStaticInExternC(D, Fn);
 
-
   maybeSetTrivialComdat(*D, *Fn);
 
+  // Set CodeGen attributes that represent floating point environment.
+  setLLVMFunctionFEnvAttributes(D, Fn);
+
   CodeGenFunction(*this).GenerateCode(GD, Fn, FI);
 
   setNonAliasAttributes(GD, Fn);
diff --git a/clang/lib/Parse/ParsePragma.cpp b/clang/lib/Parse/ParsePragma.cpp
--- a/clang/lib/Parse/ParsePragma.cpp
+++ b/clang/lib/Parse/ParsePragma.cpp
@@ -106,10 +106,6 @@
     tok::OnOffSwitch OOS;
     if (PP.LexOnOffSwitch(OOS))
      return;
-    if (OOS == tok::OOS_ON) {
-      PP.Diag(Tok, diag::warn_stdc_fenv_access_not_supported);
-      return;
-    }
 
     MutableArrayRef<Token> Toks(PP.getPreprocessorAllocator().Allocate<Token>(1),
                                 1);
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -366,7 +366,8 @@
 
   case tok::annot_pragma_fenv_access:
     ProhibitAttributes(Attrs);
-    HandlePragmaFEnvAccess();
+    Diag(Tok, diag::err_pragma_stdc_fenv_access_scope);
+    ConsumeAnnotationToken();
     return StmtEmpty();
 
   case tok::annot_pragma_fenv_round:
@@ -1033,9 +1034,9 @@
                                 Tok.getLocation(),
                                 "in compound statement ('{}')");
 
-  // Record the state of the FPFeatures, restore on leaving the
+  // Record the current FPFeatures, restore on leaving the
   // compound statement.
-  Sema::FPFeaturesStateRAII SaveFPContractState(Actions);
+  Sema::FPFeaturesStateRAII SaveFPFeatures(Actions);
 
   InMessageExpressionRAIIObject InMessage(*this, false);
   BalancedDelimiterTracker T(*this, tok::l_brace);
@@ -1046,6 +1047,7 @@
 
   // Parse any pragmas at the beginning of the compound statement.
   ParseCompoundStatementLeadingPragmas();
+  Actions.ActOnAfterCompoundStatementLeadingPragmas();
 
   StmtVector Stmts;
 
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -389,6 +389,13 @@
   PopCompoundScope();
 }
 
+void Sema::ActOnAfterCompoundStatementLeadingPragmas() {
+  if (getCurFPFeatures().getAllowFEnvAccess()) {
+    FunctionDecl *F = getCurFunctionDecl();
+    F->setUsesFPIntrin(true);
+  }
+}
+
 sema::CompoundScopeInfo &Sema::getCurCompoundScope() const {
   return getCurFunction()->CompoundScopes.back();
 }
diff --git a/clang/test/CXX/expr/expr.const/p2-0x.cpp b/clang/test/CXX/expr/expr.const/p2-0x.cpp
--- a/clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ b/clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -280,6 +280,16 @@
     constexpr float f10 = f2 - f2; // expected-error {{constant expression}} expected-note {{produces a NaN}}
     constexpr float f11 = f2 + f4; // expected-error {{constant expression}} expected-note {{produces a NaN}}
     constexpr float f12 = f2 / f2; // expected-error {{constant expression}} expected-note {{produces a NaN}}
+#pragma float_control(push)
+#pragma float_control(except, on)
+constexpr float pi = 3.14f;
+constexpr unsigned ubig = 0xFFFFFFFF;
+constexpr float ce = 1.0 / 3.0; // expected-error {{constant expression}} expected-note {{floating point arithmetic suppressed in strict evaluation modes}}
+constexpr int ci = (int) pi;
+constexpr float fbig = (float) ubig; // expected-error {{constant expression}} expected-note {{floating point arithmetic suppressed in strict evaluation modes}}
+constexpr float fabspi = __builtin_fabs(pi); // expected-error {{constant expression}} expected-note {{floating point arithmetic suppressed in strict evaluation modes}}
+constexpr float negpi = -pi; // expect no error on unary operator
+#pragma float_control(pop)
     static_assert(!isinf(f1), "");
     static_assert(isinf(f2), "");
     static_assert(!isinf(f3), "");
diff --git a/clang/test/CodeGen/fp-floatcontrol-pragma.cpp b/clang/test/CodeGen/fp-floatcontrol-pragma.cpp
--- a/clang/test/CodeGen/fp-floatcontrol-pragma.cpp
+++ b/clang/test/CodeGen/fp-floatcontrol-pragma.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -DEXCEPT=1 -fcxx-exceptions -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=CHECK-NS %s
 // RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
-// RUN: %clang_cc1 -verify -DFENV_ON=1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -DFENV_ON=1 -triple x86_64-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=CHECK-FENV %s
 // RUN: %clang_cc1 -triple %itanium_abi_triple -O3 -emit-llvm -o - %s | FileCheck -check-prefix=CHECK-O3 %s
 
 // Verify float_control(precise, off) enables fast math flags on fp operations.
@@ -138,7 +138,6 @@
 // CHECK-LABEL define float  {{.*}}test_OperatorCall{{.*}}
 
 #if FENV_ON
-// expected-warning@+1{{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
 #pragma STDC FENV_ACCESS ON
 #endif
 // CHECK-LABEL: define {{.*}}callt{{.*}}
@@ -146,7 +145,21 @@
 void callt() {
   volatile float z;
   z = z * z;
-//CHECK: = fmul float
+  //CHECK-FENV: llvm.experimental.constrained.fmul{{.*}}
+}
+
+// CHECK-LABEL: define {{.*}}myAdd{{.*}}
+float myAdd(int i, float f) {
+  if (i<0)
+  return 1.0 + 2.0;
+  // Check that floating point constant folding doesn't occur if
+  // #pragma STC FENV_ACCESS is enabled.
+  //CHECK-FENV: llvm.experimental.constrained.fadd{{.*}}double 1.0{{.*}}double 2.0{{.*}}
+  //CHECK: store float 3.0{{.*}}retval{{.*}}
+  static double v = 1.0 / 3.0;
+  //CHECK-FENV: llvm.experimental.constrained.fdiv{{.*}}double 1.0{{.*}}double 3.0{{.*}}
+  //CHECK-NOT: fdiv
+  return v;
 }
 
 #if EXCEPT
diff --git a/clang/test/CodeGen/pragma-fenv_access.c b/clang/test/CodeGen/pragma-fenv_access.c
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGen/pragma-fenv_access.c
@@ -0,0 +1,66 @@
+// xxx: %clang_cc1 -ffp-exception-behavior=strict -frounding-math -triple %itanium_abi_triple -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -ffp-exception-behavior=strict -triple %itanium_abi_triple -emit-llvm %s -o - | FileCheck %s
+
+#pragma STDC FENV_ACCESS ON
+
+float func_01(float x, float y) {
+  return x + y;
+}
+// CHECK-LABEL: @func_01
+// CHECK: call float @llvm.experimental.constrained.fadd.f32(float {{.*}}, float {{.*}}, metadata !"round.tonearest", metadata !"fpexcept.strict")
+
+
+float func_02(float x, float y) {
+  #pragma float_control(except, off)
+  #pragma STDC FENV_ACCESS OFF
+  return x + y;
+}
+// CHECK-LABEL: @func_02
+// CHECK: fadd float {{.*}}
+
+
+float func_03(float x, float y) {
+  return x + y;
+}
+// CHECK-LABEL: @func_03
+// CHECK: call float @llvm.experimental.constrained.fadd.f32(float {{.*}}, float {{.*}}, metadata !"round.tonearest", metadata !"fpexcept.strict")
+
+
+#pragma STDC FENV_ACCESS OFF
+
+float func_04(float x, float y) {
+  #pragma float_control(except, off)
+  return x + y;
+}
+// CHECK-LABEL: @func_04
+// CHECK: fadd float {{.*}}
+
+
+float func_05(float x, float y) {
+  #pragma STDC FENV_ACCESS ON
+  return x + y;
+}
+// CHECK-LABEL: @func_05
+// CHECK: call float @llvm.experimental.constrained.fadd.f32(float {{.*}}, float {{.*}}, metadata !"round.tonearest", metadata !"fpexcept.strict")
+
+
+float func_06(float x, float y) {
+  #pragma float_control(except, off)
+  return x + y;
+}
+// CHECK-LABEL: @func_06
+// CHECK: fadd float {{.*}}
+
+
+float func_07(float x, float y) {
+  x -= y;
+  if (x) {
+    #pragma STDC FENV_ACCESS ON
+    y *= 2;
+  }
+  return y + 4;
+}
+// CHECK-LABEL: @func_07
+// CHECK: call float @llvm.experimental.constrained.fsub.f32(float {{.*}}, float {{.*}}, metadata !"round.tonearest", metadata !"fpexcept.strict")
+// CHECK: call float @llvm.experimental.constrained.fmul.f32(float {{.*}}, float {{.*}}, metadata !"round.tonearest", metadata !"fpexcept.strict")
+// CHECK: call float @llvm.experimental.constrained.fadd.f32(float {{.*}}, float {{.*}}, metadata !"round.tonearest", metadata !"fpexcept.strict")
diff --git a/clang/test/Parser/fp-floatcontrol-syntax.cpp b/clang/test/Parser/fp-floatcontrol-syntax.cpp
--- a/clang/test/Parser/fp-floatcontrol-syntax.cpp
+++ b/clang/test/Parser/fp-floatcontrol-syntax.cpp
@@ -26,19 +26,14 @@
 double a = 0.0;
 double b = 1.0;
 
-//FIXME At some point this warning will be removed, until then
-//      document the warning
-#ifdef FAST
-// expected-warning@+1{{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
-#pragma STDC FENV_ACCESS ON
-#else
-#pragma STDC FENV_ACCESS ON // expected-warning{{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
-#endif
 #ifdef STRICT
 #pragma float_control(precise, off) // expected-error {{'#pragma float_control(precise, off)' is illegal when except is enabled}}
 #else
+#ifndef FAST
 // Currently FENV_ACCESS cannot be enabled by pragma, skip error check
-#pragma float_control(precise, off) // not-expected-error {{'#pragma float_control(precise, off)' is illegal when fenv_access is enabled}}
+#pragma STDC FENV_ACCESS ON
+#pragma float_control(precise, off) // expected-error {{'#pragma float_control(precise, off)' is illegal when fenv_access is enabled}}
+#endif
 #endif
 
 #pragma float_control(precise, on)
diff --git a/clang/test/Parser/pragma-fenv_access.c b/clang/test/Parser/pragma-fenv_access.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Parser/pragma-fenv_access.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+#pragma STDC FENV_ACCESS IN_BETWEEN   // expected-warning {{expected 'ON' or 'OFF' or 'DEFAULT' in pragma}}
+
+#pragma STDC FENV_ACCESS OFF
+
+float func_04(int x, float y) {
+  if (x)
+    return y + 2;
+  #pragma STDC FENV_ACCESS ON // expected-error{{'#pragma STDC FENV_ACCESS' can only appear at file scope or at the start of a compound statement}}
+  return x + y;
+}
diff --git a/clang/test/Preprocessor/pragma_unknown.c b/clang/test/Preprocessor/pragma_unknown.c
--- a/clang/test/Preprocessor/pragma_unknown.c
+++ b/clang/test/Preprocessor/pragma_unknown.c
@@ -16,15 +16,6 @@
 // CHECK: {{^}}#pragma STDC FP_CONTRACT DEFAULT{{$}}
 // CHECK: {{^}}#pragma STDC FP_CONTRACT IN_BETWEEN{{$}}
 
-#pragma STDC FENV_ACCESS ON          // expected-warning {{pragma STDC FENV_ACCESS ON is not supported, ignoring pragma}}
-#pragma STDC FENV_ACCESS OFF
-#pragma STDC FENV_ACCESS DEFAULT
-#pragma STDC FENV_ACCESS IN_BETWEEN   // expected-warning {{expected 'ON' or 'OFF' or 'DEFAULT' in pragma}}
-// CHECK: {{^}}#pragma STDC FENV_ACCESS ON{{$}}
-// CHECK: {{^}}#pragma STDC FENV_ACCESS OFF{{$}}
-// CHECK: {{^}}#pragma STDC FENV_ACCESS DEFAULT{{$}}
-// CHECK: {{^}}#pragma STDC FENV_ACCESS IN_BETWEEN{{$}}
-
 #pragma STDC CX_LIMITED_RANGE ON
 #pragma STDC CX_LIMITED_RANGE OFF
 #pragma STDC CX_LIMITED_RANGE DEFAULT