[PATCH] D156506: [clang][Interp] Check floating results for NaNs

[Timm Bäder via Phabricator via cfe-commits]

tbaeder created this revision.
tbaeder added reviewers: aaron.ballman, erichkeane, shafik, cor3ntin.
Herald added a project: All.
tbaeder requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

This does not handle the builtin functions yet, since I'm not sure if I should 
check for all nans or only signaling ones yet.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D156506

Files:
  clang/lib/AST/Interp/Interp.cpp
  clang/lib/AST/Interp/Interp.h
  clang/test/AST/Interp/floats.cpp


Index: clang/test/AST/Interp/floats.cpp
===================================================================
--- clang/test/AST/Interp/floats.cpp
+++ clang/test/AST/Interp/floats.cpp
@@ -161,3 +161,18 @@
   static_assert(!(inf < nan), "");
   static_assert(!(inf > nan), "");
 }
+
+namespace nan {
+  constexpr double nan = __builtin_nan("");
+  static_assert(nan);
+
+  constexpr double D1 = 1 + nan; // ref-error {{must be initialized by a constant expression}} \
+                                 // ref-note {{produces a NaN}} \
+                                 // expected-error {{must be initialized by a constant expression}} \
+                                 // expected-note {{produces a NaN}}
+
+  constexpr double D2 = __builtin_inf() / __builtin_inf(); // ref-error {{must be initialized by a constant expression}} \
+                                                           // ref-note {{produces a NaN}} \
+                                                           // expected-error {{must be initialized by a constant expression}} \
+                                                           // expected-note {{produces a NaN}}
+}
Index: clang/lib/AST/Interp/Interp.h
===================================================================
--- clang/lib/AST/Interp/Interp.h
+++ clang/lib/AST/Interp/Interp.h
@@ -171,7 +171,8 @@
 
 /// Checks if the result is a floating-point operation is valid
 /// in the current context.
-bool CheckFloatResult(InterpState &S, CodePtr OpPC, APFloat::opStatus Status);
+bool CheckFloatResult(InterpState &S, CodePtr OpPC, const Floating &Result,
+                      APFloat::opStatus Status);
 
 bool CheckBitcast(InterpState &S, CodePtr OpPC, unsigned IndeterminateBits,
                   bool TargetIsUCharOrByte);
@@ -316,7 +317,7 @@
   Floating Result;
   auto Status = Floating::add(LHS, RHS, RM, &Result);
   S.Stk.push<Floating>(Result);
-  return CheckFloatResult(S, OpPC, Status);
+  return CheckFloatResult(S, OpPC, Result, Status);
 }
 
 template <PrimType Name, class T = typename PrimConv<Name>::T>
@@ -334,7 +335,7 @@
   Floating Result;
   auto Status = Floating::sub(LHS, RHS, RM, &Result);
   S.Stk.push<Floating>(Result);
-  return CheckFloatResult(S, OpPC, Status);
+  return CheckFloatResult(S, OpPC, Result, Status);
 }
 
 template <PrimType Name, class T = typename PrimConv<Name>::T>
@@ -352,7 +353,7 @@
   Floating Result;
   auto Status = Floating::mul(LHS, RHS, RM, &Result);
   S.Stk.push<Floating>(Result);
-  return CheckFloatResult(S, OpPC, Status);
+  return CheckFloatResult(S, OpPC, Result, Status);
 }
 /// 1) Pops the RHS from the stack.
 /// 2) Pops the LHS from the stack.
@@ -455,7 +456,7 @@
   Floating Result;
   auto Status = Floating::div(LHS, RHS, RM, &Result);
   S.Stk.push<Floating>(Result);
-  return CheckFloatResult(S, OpPC, Status);
+  return CheckFloatResult(S, OpPC, Result, Status);
 }
 
 //===----------------------------------------------------------------------===//
@@ -632,7 +633,7 @@
 
   Ptr.deref<Floating>() = Result;
 
-  return CheckFloatResult(S, OpPC, Status);
+  return CheckFloatResult(S, OpPC, Result, Status);
 }
 
 inline bool Incf(InterpState &S, CodePtr OpPC, llvm::RoundingMode RM) {
@@ -1586,7 +1587,7 @@
   auto Status = Floating::fromIntegral(FromAP, *Sem, RM, Result);
   S.Stk.push<Floating>(Result);
 
-  return CheckFloatResult(S, OpPC, Status);
+  return CheckFloatResult(S, OpPC, Result, Status);
 }
 
 template <PrimType Name, class T = typename PrimConv<Name>::T>
@@ -1611,7 +1612,7 @@
     }
 
     S.Stk.push<T>(T(Result));
-    return CheckFloatResult(S, OpPC, Status);
+    return CheckFloatResult(S, OpPC, F, Status);
   }
 }
 
Index: clang/lib/AST/Interp/Interp.cpp
===================================================================
--- clang/lib/AST/Interp/Interp.cpp
+++ clang/lib/AST/Interp/Interp.cpp
@@ -494,13 +494,25 @@
   return false;
 }
 
-bool CheckFloatResult(InterpState &S, CodePtr OpPC, APFloat::opStatus Status) {
+bool CheckFloatResult(InterpState &S, CodePtr OpPC, const Floating &Result,
+                      APFloat::opStatus Status) {
+  const SourceInfo &E = S.Current->getSource(OpPC);
+
+  // [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 (Result.isNan()) {
+    S.CCEDiag(E, diag::note_constexpr_float_arithmetic)
+        << /*NaN=*/true << S.Current->getRange(OpPC);
+    return S.noteUndefinedBehavior();
+  }
+
   // In a constant context, assume that any dynamic rounding mode or FP
   // exception state matches the default floating-point environment.
   if (S.inConstantContext())
     return true;
 
-  const SourceInfo &E = S.Current->getSource(OpPC);
   FPOptions FPO = E.asExpr()->getFPFeaturesInEffect(S.Ctx.getLangOpts());
 
   if ((Status & APFloat::opInexact) &&

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