[Fixed Point Arithmetic] Fixed Point Addition

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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@351364 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 76 insertions, 6 deletions

diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index 1c14d4c99a..6b3c78121b 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/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 @@ public:
 
   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 @@ public:
     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 &),
@@ -1423,10 +1436,6 @@ 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());
 
@@ -1434,6 +1443,16 @@ Value *ScalarExprEmitter::EmitFixedPointConversion(Value *Src, QualType SrcTy,
       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()) {