Index: clang/include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticASTKinds.td
+++ clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -371,6 +371,15 @@
 def warn_fixedpoint_constant_overflow : Warning<
   "overflow in expression; result is %0 with type %1">,
   InGroup<DiagGroup<"fixed-point-overflow">>;
+def warn_fp_infinity : Warning<
+  "floating-point infinity may be optimized out of computation or comparison">,
+  InGroup<LiteralRange>;
+def warn_fp_nan: Warning<
+  "floating-point NaN may be optimized out of computation or comparison">,
+  InGroup<LiteralRange>;
+def warn_fp_negzero: Warning<
+  "floating-point -0.0 may be optimized out of computation or comparison">,
+  InGroup<LiteralRange>;
 
 // This is a temporary diagnostic, and shall be removed once our
 // implementation is complete, and like the preceding constexpr notes belongs
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -13563,10 +13563,22 @@
 };
 } // end anonymous namespace
 
-static bool EvaluateFloat(const Expr* E, APFloat& Result, EvalInfo &Info) {
+static bool EvaluateFloat(const Expr *E, APFloat &Result, EvalInfo &Info) {
   assert(!E->isValueDependent());
   assert(E->isPRValue() && E->getType()->isRealFloatingType());
-  return FloatExprEvaluator(Info, Result).Visit(E);
+  bool Status = FloatExprEvaluator(Info, Result).Visit(E);
+
+  // Warn if we encounter a floating-point special value that is potentially
+  // constant-folded by the optimizer.
+  const FPOptions &FPO = E->getFPFeaturesInEffect(Info.Ctx.getLangOpts());
+  if (Result.isInfinity() && FPO.getNoHonorInfs())
+    Info.Ctx.getDiagnostics().Report(E->getExprLoc(), diag::warn_fp_infinity);
+  else if (Result.isNaN() && FPO.getNoHonorNaNs())
+    Info.Ctx.getDiagnostics().Report(E->getExprLoc(), diag::warn_fp_nan);
+  else if (Result.isNegZero() && FPO.getNoSignedZero())
+    Info.Ctx.getDiagnostics().Report(E->getExprLoc(), diag::warn_fp_negzero);
+
+  return Status;
 }
 
 static bool TryEvaluateBuiltinNaN(const ASTContext &Context,
Index: clang/test/AST/warn-fp-values.c
===================================================================
--- /dev/null
+++ clang/test/AST/warn-fp-values.c
@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 %s -triple x86_64-unknown-unknown -verify -fsyntax-only -ffast-math -Wliteral-range
+
+#define INFINITY_MATH_MACRO  1.0 / 0.0
+
+#define NAN_MATH_MACRO  0.0f / 0.0f
+
+// Infinity
+
+double inf_by_macro() {
+  double d = INFINITY_MATH_MACRO; // expected-warning {{floating-point infinity may be optimized}}
+  return d;
+}
+
+float inf_by_overflow() {
+  const float huge_literal = 10e100f; // expected-warning {{magnitude of floating-point constant too large}} {{floating-point infinity may be optimized}}
+  return huge_literal;
+}
+
+double inf_by_builtin() {
+  double b = __builtin_inf(); // shows warning if compile continues with -emit-llvm
+  return b;
+}
+
+float inf_by_builtin_cast() {
+  float b = __builtin_inf(); // expected-warning {{floating-point infinity may be optimized}}
+  return b;
+}
+
+// NaN
+
+float nan_by_macro() {
+  float f = NAN_MATH_MACRO; // expected-warning {{floating-point NaN may be optimized}}
+  return f;
+}
+
+double nan_by_builtin() {
+  double b = __builtin_nan(""); // shows warning if compile continues with -emit-llvm
+  return b;
+}
+
+float nan_by_builtin_cast() {
+  float b = __builtin_nan(""); // expected-warning {{floating-point NaN may be optimized}}
+  return b;
+}
+
+// -0.0
+
+double neg_zero_literal() {
+  return -0.0; // shows warning if compile continues with -emit-llvm
+}