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Split out from https://reviews.llvm.org/D156506.
Before adding this behavior to the new constexpr interpreter, I'd like to first
see it in the current one.
This patch removes the checks for a NaN result of floating point operations and
instead checks the input operands for signaling NaNs.
There are only three tests for the NaN-result check as far as I can see, so I
added a few new ones.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D157072
Files:
clang/include/clang/Basic/DiagnosticASTKinds.td
clang/lib/AST/ExprConstant.cpp
clang/test/CXX/expr/expr.const/p2-0x.cpp
clang/test/SemaCXX/constexpr-float.cpp
Index: clang/test/SemaCXX/constexpr-float.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/constexpr-float.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+
+template<typename T>
+constexpr bool isNan(T V) {
+ return __builtin_isnan(V);
+}
+
+constexpr double Signaling = __builtin_nans("");
+static_assert(isNan(Signaling), "");
+constexpr double Quiet = __builtin_nan("");
+static_assert(isNan(Quiet), "");
+
+
+static_assert(Signaling + 1 == 0, ""); // expected-error {{not an integral constant expression}} \
+ // expected-note {{NaN input to a floating point operation}}
+static_assert(Signaling - 1 == 0, ""); // expected-error {{not an integral constant expression}} \
+ // expected-note {{NaN input to a floating point operation}}
+static_assert(Signaling / 1 == 0, ""); // expected-error {{not an integral constant expression}} \
+ // expected-note {{NaN input to a floating point operation}}
+static_assert(Signaling * 1 == 0, ""); // expected-error {{not an integral constant expression}} \
+ // expected-note {{NaN input to a floating point operation}}
+
+static_assert(Quiet + 1 != 0, "");
+static_assert(isNan(Quiet + 1), "");
+static_assert(-Signaling != 0, "");
+static_assert(+Signaling != 0, "");
Index: clang/test/CXX/expr/expr.const/p2-0x.cpp
===================================================================
--- clang/test/CXX/expr/expr.const/p2-0x.cpp
+++ clang/test/CXX/expr/expr.const/p2-0x.cpp
@@ -278,9 +278,9 @@
constexpr float f7 = 0.f / 0.f; // expected-error {{constant expression}} expected-note {{division by zero}}
constexpr float f8 = 1.f / 0.f; // expected-error {{constant expression}} expected-note {{division by zero}}
constexpr float f9 = 1e308 / 1e-308; // ok, +inf
- 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}}
+ constexpr float f10 = f2 - f2;
+ constexpr float f11 = f2 + f4;
+ constexpr float f12 = f2 / f2;
#pragma float_control(push)
#pragma float_control(except, on)
constexpr float pi = 3.14f;
Index: clang/lib/AST/ExprConstant.cpp
===================================================================
--- clang/lib/AST/ExprConstant.cpp
+++ clang/lib/AST/ExprConstant.cpp
@@ -2628,6 +2628,16 @@
return RM;
}
+/// Signaling NaNs are invalid inputs to floating point operations.
+static bool checkFloatingPointInput(EvalInfo &Info, const Expr *E,
+ const APFloat &Input) {
+ if (!Input.isSignaling())
+ return true;
+
+ Info.CCEDiag(E, diag::note_constexpr_float_nan_input) << E->getSourceRange();
+ return Info.noteUndefinedBehavior();
+}
+
/// Check if the given evaluation result is allowed for constant evaluation.
static bool checkFloatingPointResult(EvalInfo &Info, const Expr *E,
APFloat::opStatus St) {
@@ -2904,6 +2914,10 @@
static bool handleFloatFloatBinOp(EvalInfo &Info, const BinaryOperator *E,
APFloat &LHS, BinaryOperatorKind Opcode,
const APFloat &RHS) {
+ if (!checkFloatingPointInput(Info, E->getLHS(), LHS) ||
+ !checkFloatingPointInput(Info, E->getRHS(), RHS))
+ return false;
+
llvm::RoundingMode RM = getActiveRoundingMode(Info, E);
APFloat::opStatus St;
switch (Opcode) {
@@ -2928,15 +2942,6 @@
break;
}
- // [expr.pre]p4:
- // If during the evaluation of an expression, the result is not
- // mathematically defined [...], the behavior is undefined.
- // FIXME: C++ rules require us to not conform to IEEE 754 here.
- if (LHS.isNaN()) {
- Info.CCEDiag(E, diag::note_constexpr_float_arithmetic) << LHS.isNaN();
- return Info.noteUndefinedBehavior();
- }
-
return checkFloatingPointResult(Info, E, St);
}
Index: clang/include/clang/Basic/DiagnosticASTKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticASTKinds.td
+++ clang/include/clang/Basic/DiagnosticASTKinds.td
@@ -79,6 +79,8 @@
"in a constant expression">;
def note_constexpr_float_arithmetic : Note<
"floating point arithmetic produces %select{an infinity|a NaN}0">;
+def note_constexpr_float_nan_input : Note<
+ "NaN input to a floating point operation">;
def note_constexpr_dynamic_rounding : Note<
"cannot evaluate this expression if rounding mode is dynamic">;
def note_constexpr_float_arithmetic_strict : Note<
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