[clang][Interp] Fully serialize Floating values to bytes

The Floating class wraps a APFloat, which might heap allocate memory to
represent large floating values. When writing those to bytecode, we
would free() the heap allocation after writing, when destroying the
actual APFloat we wrote.

Fix this by seralizing a Floating as Semantics + APInt.

This will be neccessary in more cases later, when we support
arbitrary-precision integers or _BitInt.

Differential Revision: https://reviews.llvm.org/D155165

Author: tbaederr

clang/lib/AST/Interp/ByteCodeEmitter.cpp

@@ -207,6 +207,25 @@ static void emit(Program &P, std::vector<std::byte> &Code, const T &Val,
   }
 }
 
+template <>
+void emit(Program &P, std::vector<std::byte> &Code, const Floating &Val,
+          bool &Success) {
+  size_t Size = Val.bytesToSerialize();
+
+  if (Code.size() + Size > std::numeric_limits<unsigned>::max()) {
+    Success = false;
+    return;
+  }
+
+  // Access must be aligned!
+  size_t ValPos = align(Code.size());
+  Size = align(Size);
+  assert(aligned(ValPos + Size));
+  Code.resize(ValPos + Size);
+
+  Val.serialize(Code.data() + ValPos);
+}
+
 template <typename... Tys>
 bool ByteCodeEmitter::emitOp(Opcode Op, const Tys &... Args, const SourceInfo &SI) {
   bool Success = true;

clang/lib/AST/Interp/Disasm.cpp

@@ -31,6 +31,12 @@ template <typename T> inline T ReadArg(Program &P, CodePtr &OpPC) {
   }
 }
 
+template <> inline Floating ReadArg<Floating>(Program &P, CodePtr &OpPC) {
+  Floating F = Floating::deserialize(*OpPC);
+  OpPC += align(F.bytesToSerialize());
+  return F;
+}
+
 LLVM_DUMP_METHOD void Function::dump() const { dump(llvm::errs()); }
 
 LLVM_DUMP_METHOD void Function::dump(llvm::raw_ostream &OS) const {

clang/lib/AST/Interp/Floating.h

@@ -119,6 +119,36 @@ class Floating final {
     return Status;
   }
 
+  static Floating bitcastFromMemory(const std::byte *Buff,
+                                    const llvm::fltSemantics &Sem) {
+    size_t Size = APFloat::semanticsSizeInBits(Sem);
+    llvm::APInt API(Size, true);
+    llvm::LoadIntFromMemory(API, (const uint8_t *)Buff, Size / 8);
+
+    return Floating(APFloat(Sem, API));
+  }
+
+  // === Serialization support ===
+  size_t bytesToSerialize() const {
+    return sizeof(llvm::fltSemantics *) +
+           (APFloat::semanticsSizeInBits(F.getSemantics()) / 8);
+  }
+
+  void serialize(std::byte *Buff) const {
+    // Semantics followed by an APInt.
+    *reinterpret_cast<const llvm::fltSemantics **>(Buff) = &F.getSemantics();
+
+    llvm::APInt API = F.bitcastToAPInt();
+    llvm::StoreIntToMemory(API, (uint8_t *)(Buff + sizeof(void *)),
+                           bitWidth() / 8);
+  }
+
+  static Floating deserialize(const std::byte *Buff) {
+    const llvm::fltSemantics *Sem;
+    std::memcpy((void *)&Sem, Buff, sizeof(void *));
+    return bitcastFromMemory(Buff + sizeof(void *), *Sem);
+  }
+
   static Floating abs(const Floating &F) {
     APFloat V = F.F;
     if (V.isNegative())

clang/lib/AST/Interp/Interp.h

@@ -1806,6 +1806,12 @@ template <typename T> inline T ReadArg(InterpState &S, CodePtr &OpPC) {
   }
 }
 
+template <> inline Floating ReadArg<Floating>(InterpState &S, CodePtr &OpPC) {
+  Floating F = Floating::deserialize(*OpPC);
+  OpPC += align(F.bytesToSerialize());
+  return F;
+}
+
 } // namespace interp
 } // namespace clang
 

clang/lib/AST/Interp/Source.h

@@ -43,6 +43,7 @@ class CodePtr final {
   }
 
   bool operator!=(const CodePtr &RHS) const { return Ptr != RHS.Ptr; }
+  const std::byte *operator*() const { return Ptr; }
 
   operator bool() const { return Ptr; }
 

clang/test/AST/Interp/floats.cpp

@@ -144,6 +144,22 @@ namespace ZeroInit {
 
 namespace LongDouble {
   constexpr long double ld = 3.1425926539;
+
+  constexpr long double f() {
+    const long double L = __LDBL_MAX__;
+
+    return L;
+  };
+  static_assert(f() == __LDBL_MAX__);
+
+#ifdef __FLOAT128__
+  constexpr __float128 f128() {
+    const __float128 L = __LDBL_MAX__;
+
+    return L;
+  };
+  static_assert(f128() == __LDBL_MAX__);
+#endif
 }
 
 namespace Compare {