APFloat: allow 64-bit of payload

[jfb]

Summary

The APFloat and Constant APIs taking an APInt allow arbitrary payloads, and that's great. There's a convenience API which takes an unsigned, and that's silly because it then directly creates a 64-bit APInt. Just change it to 64-bits directly.

[jfb]

Testing-wise, this isn't tested in APFloatTest.cpp, so I'm keeping the status-quo.
The only place where it's used in an odd way is for the floating-literals.s test (which tries to match the GNU as behavior). The test makes me uneasy because it's using ~0 to create a .single NaN... and I have no idea what's the right behavior for .double... This is better fixed in a follow-up.

[rjmccall]

This truncates the payload to fit into the significand field. Presumably that includes setting the top bit of the significand to make this a NaN and not an infinity. Does it also always form a qNaN, or can you create an sNaN this way?

[jfb]

In D55460#1324136, @rjmccall wrote:

This truncates the payload to fit into the significand field. Presumably that includes setting the top bit of the significand to make this a NaN and not an infinity. Does it also always form a qNaN, or can you create an sNaN this way?

Someone wrote a test for this! http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/APFloatTest.cpp?r1=97364&r2=97363&pathrev=97364

[rjmccall]

In D55460#1324143, @jfb wrote:

In D55460#1324136, @rjmccall wrote:

This truncates the payload to fit into the significand field. Presumably that includes setting the top bit of the significand to make this a NaN and not an infinity. Does it also always form a qNaN, or can you create an sNaN this way?

Someone wrote a test for this! http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/APFloatTest.cpp?r1=97364&r2=97363&pathrev=97364

Heh, blast from the past. I guess I could also have looked at the right implementation to see that it always made a qNaN.

Anyway, yes, this seems reasonable.

[rjmccall]

Oh, actually, please embellish the unit test to include some >32-bit payloads when building double-typed NaNs.

[jfb]

• Add tests

[jfb]

In D55460#1324156, @rjmccall wrote:

Oh, actually, please embellish the unit test to include some >32-bit payloads when building double-typed NaNs.

Done, I added some for 32-bit as well, where the original weren't touching top bits either.

[jfb]

• Also add ConstantFP NaN getters which match the APFloat ones (with getQNaN / getSNaN and APInt parameters).

[rjmccall]

LGTM.

include/llvm/ADT/APFloat.h

static APFloat getInf(const fltSemantics &Sem, bool Negative = false) {
     APFloat Val(Sem, uninitialized);
     Val.makeInf(Negative);
     return Val;
   }
 
   /// Factory for NaN values.
   ///
   /// \param Negative - True iff the NaN generated should be negative.
-  /// \param type - The unspecified fill bits for creating the NaN, 0 by
+  /// \param payload - The unspecified fill bits for creating the NaN, 0 by
   /// default.  The value is truncated as necessary.
   static APFloat getNaN(const fltSemantics &Sem, bool Negative = false,
-                        unsigned type = 0) {
-    if (type) {
-      APInt fill(64, type);
-      return getQNaN(Sem, Negative, &fill);
+                        uint64_t payload = 0) {
+    if (payload) {
+      APInt intPayload(64, payload);
+      return getQNaN(Sem, Negative, &intPayload);
     } else {
       return getQNaN(Sem, Negative, nullptr);
     }
   }
 
   /// Factory for QNaN values.
   static APFloat getQNaN(const fltSemantics &Sem, bool Negative = false,
                          const APInt *payload = nullptr) {

include/llvm/IR/Constants.h

public:
   static Constant *get(Type* Ty, double V);
 
   /// If Ty is a vector type, return a Constant with a splat of the given
   /// value. Otherwise return a ConstantFP for the given value.
   static Constant *get(Type *Ty, const APFloat &V);
 
   static Constant *get(Type* Ty, StringRef Str);
   static ConstantFP *get(LLVMContext &Context, const APFloat &V);
-  static Constant *getNaN(Type *Ty, bool Negative = false, unsigned type = 0);
+  static Constant *getNaN(Type *Ty, bool Negative = false, uint64_t Payload = 0);
+  static Constant *getQNaN(Type *Ty, bool Negative = false,
+                           APInt *Payload = nullptr);
+  static Constant *getSNaN(Type *Ty, bool Negative = false,
+                           APInt *Payload = nullptr);
   static Constant *getNegativeZero(Type *Ty);
   static Constant *getInfinity(Type *Ty, bool Negative = false);
 
   /// Return true if Ty is big enough to represent V.
   static bool isValueValidForType(Type *Ty, const APFloat &V);
   inline const APFloat &getValueAPF() const { return Val; }
 
   /// Return true if the value is positive or negative zero.

lib/IR/Constants.cpp

Constant *ConstantFP::get(Type *Ty, StringRef Str) {
 
   // For vectors, broadcast the value.
   if (VectorType *VTy = dyn_cast<VectorType>(Ty))
     return ConstantVector::getSplat(VTy->getNumElements(), C);
 
   return C;
 }
 
-Constant *ConstantFP::getNaN(Type *Ty, bool Negative, unsigned Type) {
+Constant *ConstantFP::getNaN(Type *Ty, bool Negative, uint64_t Payload) {
   const fltSemantics &Semantics = *TypeToFloatSemantics(Ty->getScalarType());
-  APFloat NaN = APFloat::getNaN(Semantics, Negative, Type);
+  APFloat NaN = APFloat::getNaN(Semantics, Negative, Payload);
+  Constant *C = get(Ty->getContext(), NaN);
+
+  if (VectorType *VTy = dyn_cast<VectorType>(Ty))
+    return ConstantVector::getSplat(VTy->getNumElements(), C);
+
+  return C;
+}
+
+Constant *ConstantFP::getQNaN(Type *Ty, bool Negative, APInt *Payload) {
+  const fltSemantics &Semantics = *TypeToFloatSemantics(Ty->getScalarType());
+  APFloat NaN = APFloat::getQNaN(Semantics, Negative, Payload);
+  Constant *C = get(Ty->getContext(), NaN);
+  
+  if (VectorType *VTy = dyn_cast<VectorType>(Ty))
+    return ConstantVector::getSplat(VTy->getNumElements(), C);
+  
+  return C;
+}
+
+Constant *ConstantFP::getSNaN(Type *Ty, bool Negative, APInt *Payload) {
+  const fltSemantics &Semantics = *TypeToFloatSemantics(Ty->getScalarType());
+  APFloat NaN = APFloat::getSNaN(Semantics, Negative, Payload);
   Constant *C = get(Ty->getContext(), NaN);
   
   if (VectorType *VTy = dyn_cast<VectorType>(Ty))
     return ConstantVector::getSplat(VTy->getNumElements(), C);
   
   return C;
 }
 
 Constant *ConstantFP::getNegativeZero(Type *Ty) {
   const fltSemantics &Semantics = *TypeToFloatSemantics(Ty->getScalarType());
   APFloat NegZero = APFloat::getZero(Semantics, /*Negative=*/true);
   Constant *C = get(Ty->getContext(), NegZero);
 

unittests/ADT/APFloatTest.cpp

TEST(APFloatTest, toInteger) {
 
   EXPECT_EQ(APFloat::opInvalidOp,
             APFloat(APFloat::IEEEdouble(), "16")
             .convertToInteger(result, APFloat::rmTowardZero, &isExact));
   EXPECT_FALSE(isExact);
   EXPECT_EQ(APSInt::getMaxValue(5, false), result);
 }
 
-static APInt nanbits(const fltSemantics &Sem,
-                     bool SNaN, bool Negative, uint64_t fill) {
-  APInt apfill(64, fill);
+static APInt nanbitsFromAPInt(const fltSemantics &Sem, bool SNaN, bool Negative,
+                              uint64_t payload) {
+  APInt appayload(64, payload);
   if (SNaN)
-    return APFloat::getSNaN(Sem, Negative, &apfill).bitcastToAPInt();
+    return APFloat::getSNaN(Sem, Negative, &appayload).bitcastToAPInt();
   else
-    return APFloat::getQNaN(Sem, Negative, &apfill).bitcastToAPInt();
+    return APFloat::getQNaN(Sem, Negative, &appayload).bitcastToAPInt();
 }
 
 TEST(APFloatTest, makeNaN) {
-  ASSERT_EQ(0x7fc00000, nanbits(APFloat::IEEEsingle(), false, false, 0));
-  ASSERT_EQ(0xffc00000, nanbits(APFloat::IEEEsingle(), false, true, 0));
-  ASSERT_EQ(0x7fc0ae72, nanbits(APFloat::IEEEsingle(), false, false, 0xae72));
-  ASSERT_EQ(0x7fffae72, nanbits(APFloat::IEEEsingle(), false, false, 0xffffae72));
-  ASSERT_EQ(0x7fa00000, nanbits(APFloat::IEEEsingle(), true, false, 0));
-  ASSERT_EQ(0xffa00000, nanbits(APFloat::IEEEsingle(), true, true, 0));
-  ASSERT_EQ(0x7f80ae72, nanbits(APFloat::IEEEsingle(), true, false, 0xae72));
-  ASSERT_EQ(0x7fbfae72, nanbits(APFloat::IEEEsingle(), true, false, 0xffffae72));
-
-  ASSERT_EQ(0x7ff8000000000000ULL, nanbits(APFloat::IEEEdouble(), false, false, 0));
-  ASSERT_EQ(0xfff8000000000000ULL, nanbits(APFloat::IEEEdouble(), false, true, 0));
-  ASSERT_EQ(0x7ff800000000ae72ULL, nanbits(APFloat::IEEEdouble(), false, false, 0xae72));
-  ASSERT_EQ(0x7fffffffffffae72ULL, nanbits(APFloat::IEEEdouble(), false, false, 0xffffffffffffae72ULL));
-  ASSERT_EQ(0x7ff4000000000000ULL, nanbits(APFloat::IEEEdouble(), true, false, 0));
-  ASSERT_EQ(0xfff4000000000000ULL, nanbits(APFloat::IEEEdouble(), true, true, 0));
-  ASSERT_EQ(0x7ff000000000ae72ULL, nanbits(APFloat::IEEEdouble(), true, false, 0xae72));
-  ASSERT_EQ(0x7ff7ffffffffae72ULL, nanbits(APFloat::IEEEdouble(), true, false, 0xffffffffffffae72ULL));
+  const struct {
+    uint64_t expected;
+    const fltSemantics &semantics;
+    bool SNaN;
+    bool Negative;
+    uint64_t payload;
+  } tests[] = {
+    /*             expected              semantics   SNaN    Neg                payload */
+    {         0x7fc00000ULL, APFloat::IEEEsingle(), false, false,         0x00000000ULL },
+    {         0xffc00000ULL, APFloat::IEEEsingle(), false,  true,         0x00000000ULL },
+    {         0x7fc0ae72ULL, APFloat::IEEEsingle(), false, false,         0x0000ae72ULL },
+    {         0x7fffae72ULL, APFloat::IEEEsingle(), false, false,         0xffffae72ULL },
+    {         0x7fdaae72ULL, APFloat::IEEEsingle(), false, false,         0x00daae72ULL },
+    {         0x7fa00000ULL, APFloat::IEEEsingle(),  true, false,         0x00000000ULL },
+    {         0xffa00000ULL, APFloat::IEEEsingle(),  true,  true,         0x00000000ULL },
+    {         0x7f80ae72ULL, APFloat::IEEEsingle(),  true, false,         0x0000ae72ULL },
+    {         0x7fbfae72ULL, APFloat::IEEEsingle(),  true, false,         0xffffae72ULL },
+    {         0x7f9aae72ULL, APFloat::IEEEsingle(),  true, false,         0x001aae72ULL },
+    { 0x7ff8000000000000ULL, APFloat::IEEEdouble(), false, false, 0x0000000000000000ULL },
+    { 0xfff8000000000000ULL, APFloat::IEEEdouble(), false,  true, 0x0000000000000000ULL },
+    { 0x7ff800000000ae72ULL, APFloat::IEEEdouble(), false, false, 0x000000000000ae72ULL },
+    { 0x7fffffffffffae72ULL, APFloat::IEEEdouble(), false, false, 0xffffffffffffae72ULL },
+    { 0x7ffdaaaaaaaaae72ULL, APFloat::IEEEdouble(), false, false, 0x000daaaaaaaaae72ULL },
+    { 0x7ff4000000000000ULL, APFloat::IEEEdouble(),  true, false, 0x0000000000000000ULL },
+    { 0xfff4000000000000ULL, APFloat::IEEEdouble(),  true,  true, 0x0000000000000000ULL },
+    { 0x7ff000000000ae72ULL, APFloat::IEEEdouble(),  true, false, 0x000000000000ae72ULL },
+    { 0x7ff7ffffffffae72ULL, APFloat::IEEEdouble(),  true, false, 0xffffffffffffae72ULL },
+    { 0x7ff1aaaaaaaaae72ULL, APFloat::IEEEdouble(),  true, false, 0x0001aaaaaaaaae72ULL },
+  };
+
+  for (const auto &t : tests) {
+    ASSERT_EQ(t.expected, nanbitsFromAPInt(t.semantics, t.SNaN, t.Negative, t.payload));
+  }
 }
 
 #ifdef GTEST_HAS_DEATH_TEST
 #ifndef NDEBUG
 TEST(APFloatTest, SemanticsDeath) {
   EXPECT_DEATH(APFloat(APFloat::IEEEsingle(), 0.0f).convertToDouble(), "Float semantics are not IEEEdouble");
   EXPECT_DEATH(APFloat(APFloat::IEEEdouble(), 0.0 ).convertToFloat(),  "Float semantics are not IEEEsingle");
 }