[Fixed Point Arithmetic] Fixed Point Addition

PiJoules · PiJoules · commit 2044ac89aa52 · 2019-01-16T18:13:59.000Z
This patch covers addition between fixed point types and other fixed point types or integers, using the conversion rules described in 4.1.4 of N1169. Usual arithmetic rules do not apply to binary operations when one of the operands is a fixed point type, and the result of the operation must be calculated with the full precision of the operands, so we should not perform any casting to a common type. This patch does not include constant expression evaluation for addition of fixed point types. That will be addressed in another patch since I think this one is already big enough. Differential Revision: https://reviews.llvm.org/D53738 llvm-svn: 351364
diff --git a/clang/include/clang/AST/ASTContext.h b/clang/include/clang/AST/ASTContext.h
@@ -2624,6 +2624,12 @@ class ASTContext : public RefCountedBase<ASTContext> {
   // corresponding saturated type for a given fixed point type.
   QualType getCorrespondingSaturatedType(QualType Ty) const;
 
+  // This method accepts fixed point types and returns the corresponding signed
+  // type. Unlike getCorrespondingUnsignedType(), this only accepts unsigned
+  // fixed point types because there are unsigned integer types like bool and
+  // char8_t that don't have signed equivalents.
+  QualType getCorrespondingSignedFixedPointType(QualType Ty) const;
+
   //===--------------------------------------------------------------------===//
   //                    Integer Values
   //===--------------------------------------------------------------------===//
diff --git a/clang/include/clang/AST/Type.h b/clang/include/clang/AST/Type.h
@@ -2269,6 +2269,9 @@ class Type : public ExtQualsTypeCommonBase {
   /// ISO/IEC JTC1 SC22 WG14 N1169.
   bool isFixedPointType() const;
 
+  /// Return true if this is a fixed point or integer type.
+  bool isFixedPointOrIntegerType() const;
+
   /// Return true if this is a saturated fixed point type according to
   /// ISO/IEC JTC1 SC22 WG14 N1169. This type can be signed or unsigned.
   bool isSaturatedFixedPointType() const;
@@ -6596,6 +6599,10 @@ inline bool Type::isFixedPointType() const {
   return false;
 }
 
+inline bool Type::isFixedPointOrIntegerType() const {
+  return isFixedPointType() || isIntegerType();
+}
+
 inline bool Type::isSaturatedFixedPointType() const {
   if (const auto *BT = dyn_cast<BuiltinType>(CanonicalType)) {
     return BT->getKind() >= BuiltinType::SatShortAccum &&
diff --git a/clang/include/clang/Basic/FixedPoint.h b/clang/include/clang/Basic/FixedPoint.h
@@ -18,6 +18,7 @@
 #define LLVM_CLANG_BASIC_FIXEDPOINT_H
 
 #include "llvm/ADT/APSInt.h"
+#include "llvm/Support/raw_ostream.h"
 
 namespace clang {
 
@@ -36,6 +37,8 @@ class FixedPointSemantics {
       : Width(Width), Scale(Scale), IsSigned(IsSigned),
         IsSaturated(IsSaturated), HasUnsignedPadding(HasUnsignedPadding) {
     assert(Width >= Scale && "Not enough room for the scale");
+    assert(!(IsSigned && HasUnsignedPadding) &&
+           "Cannot have unsigned padding on a signed type.");
   }
 
   unsigned getWidth() const { return Width; }
@@ -46,13 +49,31 @@ class FixedPointSemantics {
 
   void setSaturated(bool Saturated) { IsSaturated = Saturated; }
 
+  /// Return the number of integral bits represented by these semantics. These
+  /// are separate from the fractional bits and do not include the sign or
+  /// padding bit.
   unsigned getIntegralBits() const {
     if (IsSigned || (!IsSigned && HasUnsignedPadding))
       return Width - Scale - 1;
     else
       return Width - Scale;
   }
 
+  /// Return the FixedPointSemantics that allows for calculating the full
+  /// precision semantic that can precisely represent the precision and ranges
+  /// of both input values. This does not compute the resulting semantics for a
+  /// given binary operation.
+  FixedPointSemantics
+  getCommonSemantics(const FixedPointSemantics &Other) const;
+
+  /// Return the FixedPointSemantics for an integer type.
+  static FixedPointSemantics GetIntegerSemantics(unsigned Width,
+                                                 bool IsSigned) {
+    return FixedPointSemantics(Width, /*Scale=*/0, IsSigned,
+                               /*IsSaturated=*/false,
+                               /*HasUnsignedPadding=*/false);
+  }
+
 private:
   unsigned Width;
   unsigned Scale;
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
@@ -10485,7 +10485,13 @@ unsigned char ASTContext::getFixedPointIBits(QualType Ty) const {
 }
 
 FixedPointSemantics ASTContext::getFixedPointSemantics(QualType Ty) const {
-  assert(Ty->isFixedPointType());
+  assert(Ty->isFixedPointType() ||
+         Ty->isIntegerType() && "Can only get the fixed point semantics for a "
+                                "fixed point or integer type.");
+  if (Ty->isIntegerType())
+    return FixedPointSemantics::GetIntegerSemantics(getIntWidth(Ty),
+                                                    Ty->isSignedIntegerType());
+
   bool isSigned = Ty->isSignedFixedPointType();
   return FixedPointSemantics(
       static_cast<unsigned>(getTypeSize(Ty)), getFixedPointScale(Ty), isSigned,
@@ -10502,3 +10508,38 @@ APFixedPoint ASTContext::getFixedPointMin(QualType Ty) const {
   assert(Ty->isFixedPointType());
   return APFixedPoint::getMin(getFixedPointSemantics(Ty));
 }
+
+QualType ASTContext::getCorrespondingSignedFixedPointType(QualType Ty) const {
+  assert(Ty->isUnsignedFixedPointType() &&
+         "Expected unsigned fixed point type");
+  const auto *BTy = Ty->getAs<BuiltinType>();
+
+  switch (BTy->getKind()) {
+  case BuiltinType::UShortAccum:
+    return ShortAccumTy;
+  case BuiltinType::UAccum:
+    return AccumTy;
+  case BuiltinType::ULongAccum:
+    return LongAccumTy;
+  case BuiltinType::SatUShortAccum:
+    return SatShortAccumTy;
+  case BuiltinType::SatUAccum:
+    return SatAccumTy;
+  case BuiltinType::SatULongAccum:
+    return SatLongAccumTy;
+  case BuiltinType::UShortFract:
+    return ShortFractTy;
+  case BuiltinType::UFract:
+    return FractTy;
+  case BuiltinType::ULongFract:
+    return LongFractTy;
+  case BuiltinType::SatUShortFract:
+    return SatShortFractTy;
+  case BuiltinType::SatUFract:
+    return SatFractTy;
+  case BuiltinType::SatULongFract:
+    return SatLongFractTy;
+  default:
+    llvm_unreachable("Unexpected unsigned fixed point type");
+  }
+}
diff --git a/clang/lib/Basic/FixedPoint.cpp b/clang/lib/Basic/FixedPoint.cpp
@@ -112,4 +112,29 @@ APFixedPoint APFixedPoint::getMin(const FixedPointSemantics &Sema) {
   return APFixedPoint(Val, Sema);
 }
 
+FixedPointSemantics FixedPointSemantics::getCommonSemantics(
+    const FixedPointSemantics &Other) const {
+  unsigned CommonScale = std::max(getScale(), Other.getScale());
+  unsigned CommonWidth =
+      std::max(getIntegralBits(), Other.getIntegralBits()) + CommonScale;
+
+  bool ResultIsSigned = isSigned() || Other.isSigned();
+  bool ResultIsSaturated = isSaturated() || Other.isSaturated();
+  bool ResultHasUnsignedPadding = false;
+  if (!ResultIsSigned) {
+    // Both are unsigned.
+    ResultHasUnsignedPadding = hasUnsignedPadding() &&
+                               Other.hasUnsignedPadding() && !ResultIsSaturated;
+  }
+
+  // If the result is signed, add an extra bit for the sign. Otherwise, if it is
+  // unsigned and has unsigned padding, we only need to add the extra padding
+  // bit back if we are not saturating.
+  if (ResultIsSigned || ResultHasUnsignedPadding)
+    CommonWidth++;
+
+  return FixedPointSemantics(CommonWidth, CommonScale, ResultIsSigned,
+                             ResultIsSaturated, ResultHasUnsignedPadding);
+}
+
 }  // namespace clang
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -125,6 +125,13 @@ struct BinOpInfo {
         return CFP->isZero();
     return true;
   }
+
+  /// Check if either operand is a fixed point type, in which case, this
+  /// operation did not follow usual arithmetic conversion and both operands may
+  /// not be the same.
+  bool isFixedPointBinOp() const {
+    return isa<BinaryOperator>(E) && Ty->isFixedPointType();
+  }
 };
 
 static bool MustVisitNullValue(const Expr *E) {
@@ -351,6 +358,9 @@ class ScalarExprEmitter
 
   Value *EmitFixedPointConversion(Value *Src, QualType SrcTy, QualType DstTy,
                                   SourceLocation Loc);
+  Value *EmitFixedPointConversion(Value *Src, FixedPointSemantics &SrcFixedSema,
+                                  FixedPointSemantics &DstFixedSema,
+                                  SourceLocation Loc);
 
   /// Emit a conversion from the specified complex type to the specified
   /// destination type, where the destination type is an LLVM scalar type.
@@ -729,6 +739,9 @@ class ScalarExprEmitter
     return Builder.CreateOr(Ops.LHS, Ops.RHS, "or");
   }
 
+  // Helper functions for fixed point binary operations.
+  Value *EmitFixedPointAdd(const BinOpInfo &Ops);
+
   BinOpInfo EmitBinOps(const BinaryOperator *E);
   LValue EmitCompoundAssignLValue(const CompoundAssignOperator *E,
                             Value *(ScalarExprEmitter::*F)(const BinOpInfo &),
@@ -1423,17 +1436,23 @@ Value *ScalarExprEmitter::EmitScalarConversion(Value *Src, QualType SrcType,
 Value *ScalarExprEmitter::EmitFixedPointConversion(Value *Src, QualType SrcTy,
                                                    QualType DstTy,
                                                    SourceLocation Loc) {
-  using llvm::APInt;
-  using llvm::ConstantInt;
-  using llvm::Value;
-
   assert(SrcTy->isFixedPointType());
   assert(DstTy->isFixedPointType());
 
   FixedPointSemantics SrcFPSema =
       CGF.getContext().getFixedPointSemantics(SrcTy);
   FixedPointSemantics DstFPSema =
       CGF.getContext().getFixedPointSemantics(DstTy);
+  return EmitFixedPointConversion(Src, SrcFPSema, DstFPSema, Loc);
+}
+
+Value *ScalarExprEmitter::EmitFixedPointConversion(
+    Value *Src, FixedPointSemantics &SrcFPSema, FixedPointSemantics &DstFPSema,
+    SourceLocation Loc) {
+  using llvm::APInt;
+  using llvm::ConstantInt;
+  using llvm::Value;
+
   unsigned SrcWidth = SrcFPSema.getWidth();
   unsigned DstWidth = DstFPSema.getWidth();
   unsigned SrcScale = SrcFPSema.getScale();
@@ -1462,7 +1481,8 @@ Value *ScalarExprEmitter::EmitFixedPointConversion(Value *Src, QualType SrcTy,
   } else {
     // Adjust the number of fractional bits.
     if (DstScale > SrcScale) {
-      ResultWidth = SrcWidth + DstScale - SrcScale;
+      // Compare to DstWidth to prevent resizing twice.
+      ResultWidth = std::max(SrcWidth + DstScale - SrcScale, DstWidth);
       llvm::Type *UpscaledTy = Builder.getIntNTy(ResultWidth);
       Result = Builder.CreateIntCast(Result, UpscaledTy, SrcIsSigned, "resize");
       Result = Builder.CreateShl(Result, DstScale - SrcScale, "upscale");
@@ -1493,7 +1513,8 @@ Value *ScalarExprEmitter::EmitFixedPointConversion(Value *Src, QualType SrcTy,
     }
 
     // Resize the integer part to get the final destination size.
-    Result = Builder.CreateIntCast(Result, DstIntTy, SrcIsSigned, "resize");
+    if (ResultWidth != DstWidth)
+      Result = Builder.CreateIntCast(Result, DstIntTy, SrcIsSigned, "resize");
   }
   return Result;
 }
@@ -3338,9 +3359,58 @@ Value *ScalarExprEmitter::EmitAdd(const BinOpInfo &op) {
     return propagateFMFlags(V, op);
   }
 
+  if (op.isFixedPointBinOp())
+    return EmitFixedPointAdd(op);
+
   return Builder.CreateAdd(op.LHS, op.RHS, "add");
 }
 
+/// The resulting value must be calculated with exact precision, so the operands
+/// may not be the same type.
+Value *ScalarExprEmitter::EmitFixedPointAdd(const BinOpInfo &op) {
+  using llvm::APSInt;
+  using llvm::ConstantInt;
+
+  const auto *BinOp = cast<BinaryOperator>(op.E);
+  assert(BinOp->getOpcode() == BO_Add && "Expected operation to be addition");
+
+  // The result is a fixed point type and at least one of the operands is fixed
+  // point while the other is either fixed point or an int. This resulting type
+  // should be determined by Sema::handleFixedPointConversions().
+  QualType ResultTy = op.Ty;
+  QualType LHSTy = BinOp->getLHS()->getType();
+  QualType RHSTy = BinOp->getRHS()->getType();
+  ASTContext &Ctx = CGF.getContext();
+  Value *LHS = op.LHS;
+  Value *RHS = op.RHS;
+
+  auto LHSFixedSema = Ctx.getFixedPointSemantics(LHSTy);
+  auto RHSFixedSema = Ctx.getFixedPointSemantics(RHSTy);
+  auto ResultFixedSema = Ctx.getFixedPointSemantics(ResultTy);
+  auto CommonFixedSema = LHSFixedSema.getCommonSemantics(RHSFixedSema);
+
+  // Convert the operands to the full precision type.
+  Value *FullLHS = EmitFixedPointConversion(LHS, LHSFixedSema, CommonFixedSema,
+                                            BinOp->getExprLoc());
+  Value *FullRHS = EmitFixedPointConversion(RHS, RHSFixedSema, CommonFixedSema,
+                                            BinOp->getExprLoc());
+
+  // Perform the actual addition.
+  Value *Result;
+  if (ResultFixedSema.isSaturated()) {
+    llvm::Intrinsic::ID IID = ResultFixedSema.isSigned()
+                                  ? llvm::Intrinsic::sadd_sat
+                                  : llvm::Intrinsic::uadd_sat;
+    Result = Builder.CreateBinaryIntrinsic(IID, FullLHS, FullRHS);
+  } else {
+    Result = Builder.CreateAdd(FullLHS, FullRHS);
+  }
+
+  // Convert to the result type.
+  return EmitFixedPointConversion(Result, CommonFixedSema, ResultFixedSema,
+                                  BinOp->getExprLoc());
+}
+
 Value *ScalarExprEmitter::EmitSub(const BinOpInfo &op) {
   // The LHS is always a pointer if either side is.
   if (!op.LHS->getType()->isPointerTy()) {
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
diff --git a/clang/test/Frontend/fixed_point_add.c b/clang/test/Frontend/fixed_point_add.c
diff --git a/clang/test/Frontend/fixed_point_conversions.c b/clang/test/Frontend/fixed_point_conversions.c
