[Fixed Point Arithmetic] Fixed Point Subtraction

[leonardchan]

Summary

This patch covers subtraction between fixed point types and other fixed point types or integers, using the conversion rules described in 4.1.4 of N1169.

[rjmccall]

clang/lib/CodeGen/CGExprScalar.cpp

3396–3397

Please go ahead and make this a covered switch with a bunch of unimplemented cases.

[rjmccall]

clang/lib/CodeGen/CGExprScalar.cpp

3451

Please create a separate case for the non-arithmetic operators (pointer-to-member, assignment, comma) that will obviously never end up in this function.

Otherwise, LGTM.

[leonardchan]

clang/lib/CodeGen/CGExprScalar.cpp

3451

Done. Although this patch wasn't marked as ready to land, do you mean that I can commit it still with the LGTM?

[rjmccall]

I don't pay attention to "ready to land" because I assume that you're verifying that your patch actually works as promised in practice, at least as far as the tests are concerned (and presumably my review catches deeper issues). If there are substantial changes that landed after my review, then I need to re-review; otherwise, you should feel free to commit with that kind of provisional LGTM when you've satisfied the provisions.

clang/lib/CodeGen/CGExprScalar.cpp

public:
   Value *EmitXor(const BinOpInfo &Ops) {
     return Builder.CreateXor(Ops.LHS, Ops.RHS, "xor");
   }
   Value *EmitOr (const BinOpInfo &Ops) {
     return Builder.CreateOr(Ops.LHS, Ops.RHS, "or");
   }
 
   // Helper functions for fixed point binary operations.
-  Value *EmitFixedPointAdd(const BinOpInfo &Ops);
+  Value *EmitFixedPointBinOp(const BinOpInfo &Ops);
 
   BinOpInfo EmitBinOps(const BinaryOperator *E);
   LValue EmitCompoundAssignLValue(const CompoundAssignOperator *E,
                             Value *(ScalarExprEmitter::*F)(const BinOpInfo &),
                                   Value *&Result);
 
   Value *EmitCompoundAssign(const CompoundAssignOperator *E,
                             Value *(ScalarExprEmitter::*F)(const BinOpInfo &));
if (op.LHS->getType()->isFPOrFPVectorTy()) {
     if (Value *FMulAdd = tryEmitFMulAdd(op, CGF, Builder))
       return FMulAdd;
 
     Value *V = Builder.CreateFAdd(op.LHS, op.RHS, "add");
     return propagateFMFlags(V, op);
   }
 
   if (op.isFixedPointBinOp())
-    return EmitFixedPointAdd(op);
+    return EmitFixedPointBinOp(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) {
+Value *ScalarExprEmitter::EmitFixedPointBinOp(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");
+  assert((BinOp->getOpcode() == BO_Add || BinOp->getOpcode() == BO_Sub) &&
+         "Expected operation to be addition or subtraction");
 
   // 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;
+  switch (BinOp->getOpcode()) {
+  case BO_Add: {
     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);
     }
+    break;
+  }
+  case BO_Sub: {
+    if (ResultFixedSema.isSaturated()) {
+      llvm::Intrinsic::ID IID = ResultFixedSema.isSigned()
+                                    ? llvm::Intrinsic::ssub_sat
+                                    : llvm::Intrinsic::usub_sat;
+      Result = Builder.CreateBinaryIntrinsic(IID, FullLHS, FullRHS);
+    } else {
+      Result = Builder.CreateSub(FullLHS, FullRHS);
+    }
+    break;
+  }
+  case BO_PtrMemD:
+  case BO_PtrMemI:
+  case BO_Mul:
+  case BO_Div:
+  case BO_Rem:
+  case BO_Shl:
+  case BO_Shr:
+  case BO_Cmp:
+  case BO_LT:
+  case BO_GT:
+  case BO_LE:
+  case BO_GE:
+  case BO_EQ:
+  case BO_NE:
+  case BO_And:
+  case BO_Xor:
+  case BO_Or:
+  case BO_LAnd:
+  case BO_LOr:
+  case BO_Assign:
+  case BO_MulAssign:
+  case BO_DivAssign:
+  case BO_RemAssign:
+  case BO_AddAssign:
+  case BO_SubAssign:
+  case BO_ShlAssign:
+  case BO_ShrAssign:
+  case BO_AndAssign:
+  case BO_XorAssign:
+  case BO_OrAssign:
+  case BO_Comma:
+    llvm_unreachable("Found unimplemented fixed point binary operation");
+  }
 
   // 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()) {
     if (op.LHS->getType()->isFPOrFPVectorTy()) {
       // Try to form an fmuladd.
       if (Value *FMulAdd = tryEmitFMulAdd(op, CGF, Builder, true))
         return FMulAdd;
       Value *V = Builder.CreateFSub(op.LHS, op.RHS, "sub");
       return propagateFMFlags(V, op);
     }
 
+    if (op.isFixedPointBinOp())
+      return EmitFixedPointBinOp(op);
+
     return Builder.CreateSub(op.LHS, op.RHS, "sub");
   }
 
   // If the RHS is not a pointer, then we have normal pointer
   // arithmetic.
   if (!op.RHS->getType()->isPointerTy())
     return emitPointerArithmetic(CGF, op, CodeGenFunction::IsSubtraction);
 

clang/test/Frontend/fixed_point_sub.c

+// RUN: %clang_cc1 -ffixed-point -S -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,SIGNED
+// RUN: %clang_cc1 -ffixed-point -fpadding-on-unsigned-fixed-point -S -emit-llvm %s -o - | FileCheck %s --check-prefixes=CHECK,UNSIGNED
+
+void SignedSubtraction() {
+  // CHECK-LABEL: SignedSubtraction
+  short _Accum sa;
+  _Accum a, b, c, d;
+  long _Accum la;
+  unsigned short _Accum usa;
+  unsigned _Accum ua;
+  unsigned long _Accum ula;
+
+  short _Fract sf;
+  _Fract f;
+  long _Fract lf;
+  unsigned short _Fract usf;
+  unsigned _Fract uf;
+  unsigned long _Fract ulf;
+
+  // Same type
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[SA2:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i16 [[SA]], [[SA2]]
+  // CHECK-NEXT: store i16 [[SUM]], i16* %sa, align 2
+  sa = sa - sa;
+
+  // To larger scale and larger width
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[A:%[0-9]+]] = load i32, i32* %a, align 4
+  // CHECK-NEXT: [[EXT_SA:%[a-z0-9]+]] = sext i16 [[SA]] to i32
+  // CHECK-NEXT: [[SA:%[a-z0-9]+]] = shl i32 [[EXT_SA]], 8
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i32 [[SA]], [[A]]
+  // CHECK-NEXT: store i32 [[SUM]], i32* %a, align 4
+  a = sa - a;
+
+  // To same scale and smaller width
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[SF:%[0-9]+]] = load i8, i8* %sf, align 1
+  // CHECK-NEXT: [[EXT_SF:%[a-z0-9]+]] = sext i8 [[SF]] to i16
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i16 [[SA]], [[EXT_SF]]
+  // CHECK-NEXT: store i16 [[SUM]], i16* %sa, align 2
+  sa = sa - sf;
+
+  // To smaller scale and same width.
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[F:%[0-9]+]] = load i16, i16* %f, align 2
+  // CHECK-NEXT: [[EXT_SA:%[a-z0-9]+]] = sext i16 [[SA]] to i24
+  // CHECK-NEXT: [[SA:%[a-z0-9]+]] = shl i24 [[EXT_SA]], 8
+  // CHECK-NEXT: [[EXT_F:%[a-z0-9]+]] = sext i16 [[F]] to i24
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i24 [[SA]], [[EXT_F]]
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = ashr i24 [[SUM]], 8
+  // CHECK-NEXT: [[TRUNC_RES:%[a-z0-9]+]] = trunc i24 [[RES]] to i16
+  // CHECK-NEXT: store i16 [[TRUNC_RES]], i16* %sa, align 2
+  sa = sa - f;
+
+  // To smaller scale and smaller width
+  // CHECK:      [[A:%[0-9]+]] = load i32, i32* %a, align 4
+  // CHECK-NEXT: [[SF:%[0-9]+]] = load i8, i8* %sf, align 1
+  // CHECK-NEXT: [[EXT_SF:%[a-z0-9]+]] = sext i8 [[SF]] to i32
+  // CHECK-NEXT: [[SF:%[a-z0-9]+]] = shl i32 [[EXT_SF]], 8
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i32 [[A]], [[SF]]
+  // CHECK-NEXT: store i32 [[SUM]], i32* %a, align 4
+  a = a - sf;
+
+  // To larger scale and same width
+  // CHECK:      [[A:%[0-9]+]] = load i32, i32* %a, align 4
+  // CHECK-NEXT: [[LF:%[0-9]+]] = load i32, i32* %lf, align 4
+  // CHECK-NEXT: [[EXT_A:%[a-z0-9]+]] = sext i32 [[A]] to i48
+  // CHECK-NEXT: [[A:%[a-z0-9]+]] = shl i48 [[EXT_A]], 16
+  // CHECK-NEXT: [[EXT_LF:%[a-z0-9]+]] = sext i32 [[LF]] to i48
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i48 [[A]], [[EXT_LF]]
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = ashr i48 [[SUM]], 16
+  // CHECK-NEXT: [[TRUNC_RES:%[a-z0-9]+]] = trunc i48 [[RES]] to i32
+  // CHECK-NEXT: store i32 [[TRUNC_RES]], i32* %a, align 4
+  a = a - lf;
+
+  // With corresponding unsigned type
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // SIGNED-NEXT: [[SA_EXT:%[a-z0-9]+]] = sext i16 [[SA]] to i17
+  // SIGNED-NEXT: [[SA:%[a-z0-9]+]] = shl i17 [[SA_EXT]], 1
+  // SIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i17
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = sub i17 [[SA]], [[USA_EXT]]
+  // SIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = ashr i17 [[SUM]], 1
+  // SIGNED-NEXT: [[SUM:%[a-z0-9]+]] = trunc i17 [[RESULT]] to i16
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = sub i16 [[SA]], [[USA]]
+  // CHECK-NEXT: store i16 [[SUM]], i16* %sa, align 2
+  sa = sa - usa;
+
+  // With unsigned of larger scale
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[USA:%[0-9]+]] = load i32, i32* %ua, align 4
+  // SIGNED-NEXT: [[SA_EXT:%[a-z0-9]+]] = sext i16 [[SA]] to i33
+  // SIGNED-NEXT: [[SA:%[a-z0-9]+]] = shl i33 [[SA_EXT]], 9
+  // SIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i32 [[USA]] to i33
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = sub i33 [[SA]], [[USA_EXT]]
+  // SIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = ashr i33 [[SUM]], 1
+  // SIGNED-NEXT: [[SUM:%[a-z0-9]+]] = trunc i33 [[RESULT]] to i32
+  // UNSIGNED-NEXT: [[EXT_SA:%[a-z0-9]+]] = sext i16 [[SA]] to i32
+  // UNSIGNED-NEXT: [[SA:%[a-z0-9]+]] = shl i32 [[EXT_SA]], 8
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = sub i32 [[SA]], [[USA]]
+  // CHECK-NEXT: store i32 [[SUM]], i32* %a, align 4
+  a = sa - ua;
+
+  // With unsigned of smaller width
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[USF:%[0-9]+]] = load i8, i8* %usf, align 1
+  // SIGNED-NEXT: [[SA_EXT:%[a-z0-9]+]] = sext i16 [[SA]] to i17
+  // SIGNED-NEXT: [[SA:%[a-z0-9]+]] = shl i17 [[SA_EXT]], 1
+  // SIGNED-NEXT: [[USF_EXT:%[a-z0-9]+]] = zext i8 [[USF]] to i17
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = sub i17 [[SA]], [[USF_EXT]]
+  // SIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = ashr i17 [[SUM]], 1
+  // SIGNED-NEXT: [[SUM:%[a-z0-9]+]] = trunc i17 [[RESULT]] to i16
+  // UNSIGNED-NEXT: [[EXT_USF:%[a-z0-9]+]] = zext i8 [[USF]] to i16
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = sub i16 [[SA]], [[EXT_USF]]
+  // CHECK-NEXT: store i16 [[SUM]], i16* %sa, align 2
+  sa = sa - usf;
+
+  // With unsigned of larger width and smaller scale
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[ULF:%[0-9]+]] = load i32, i32* %ulf, align 4
+  // SIGNED-NEXT: [[SA_EXT:%[a-z0-9]+]] = sext i16 [[SA]] to i41
+  // SIGNED-NEXT: [[SA:%[a-z0-9]+]] = shl i41 [[SA_EXT]], 25
+  // SIGNED-NEXT: [[ULF_EXT:%[a-z0-9]+]] = zext i32 [[ULF]] to i41
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = sub i41 [[SA]], [[ULF_EXT]]
+  // SIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = ashr i41 [[SUM]], 25
+  // SIGNED-NEXT: [[RES_TRUNC:%[a-z0-9]+]] = trunc i41 [[RESULT]] to i16
+  // UNSIGNED-NEXT: [[EXT_SA:%[a-z0-9]+]] = sext i16 [[SA]] to i40
+  // UNSIGNED-NEXT: [[SA:%[a-z0-9]+]] = shl i40 [[EXT_SA]], 24
+  // UNSIGNED-NEXT: [[EXT_ULF:%[a-z0-9]+]] = zext i32 [[ULF]] to i40
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = sub i40 [[SA]], [[EXT_ULF]]
+  // UNSIGNED-NEXT: [[RES:%[a-z0-9]+]] = ashr i40 [[SUM]], 24
+  // UNSIGNED-NEXT: [[RES_TRUNC:%[a-z0-9]+]] = trunc i40 [[RES]] to i16
+  // CHECK-NEXT: store i16 [[RES_TRUNC]], i16* %sa, align 2
+  sa = sa - ulf;
+
+  // Chained additions of the same signed type should result in the same
+  // semantics width.
+  // CHECK:      [[A:%[0-9]+]] = load i32, i32* %a, align 4
+  // CHECK-NEXT: [[B:%[0-9]+]] = load i32, i32* %b, align 4
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i32 [[A]], [[B]]
+  // CHECK-NEXT: [[C:%[0-9]+]] = load i32, i32* %c, align 4
+  // CHECK-NEXT: [[SUM2:%[0-9]+]] = sub i32 [[SUM]], [[C]]
+  // CHECK-NEXT: [[D:%[0-9]+]] = load i32, i32* %d, align 4
+  // CHECK-NEXT: [[SUM3:%[0-9]+]] = sub i32 [[SUM2]], [[D]]
+  // CHECK-NEXT: store i32 [[SUM3]], i32* %a, align 4
+  a = a - b - c - d;
+}
+
+void UnsignedSubtraction() {
+  // CHECK-LABEL: UnsignedSubtraction
+  unsigned short _Accum usa;
+  unsigned _Accum ua;
+  unsigned long _Accum ula;
+
+  unsigned short _Fract usf;
+  unsigned _Fract uf;
+  unsigned long _Fract ulf;
+
+  // CHECK:      [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[USA2:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i16 [[USA]], [[USA2]]
+  // CHECK-NEXT: store i16 [[SUM]], i16* %usa, align 2
+  usa = usa - usa;
+
+  // CHECK:      [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[UA:%[0-9]+]] = load i32, i32* %ua, align 4
+  // CHECK-NEXT: [[EXT_USA:%[a-z0-9]+]] = zext i16 [[USA]] to i32
+  // CHECK-NEXT: [[USA:%[a-z0-9]+]] = shl i32 [[EXT_USA]], 8
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i32 [[USA]], [[UA]]
+  // CHECK-NEXT: store i32 [[SUM]], i32* %ua, align 4
+  ua = usa - ua;
+
+  // CHECK:      [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[USF:%[0-9]+]] = load i8, i8* %usf, align 1
+  // CHECK-NEXT: [[EXT_USF:%[a-z0-9]+]] = zext i8 [[USF]] to i16
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i16 [[USA]], [[EXT_USF]]
+  // CHECK-NEXT: store i16 [[SUM]], i16* %usa, align 2
+  usa = usa - usf;
+
+  // CHECK:      [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[UF:%[0-9]+]] = load i16, i16* %uf, align 2
+  // CHECK-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i24
+  // CHECK-NEXT: [[USA:%[a-z0-9]+]] = shl i24 [[USA_EXT]], 8
+  // CHECK-NEXT: [[UF_EXT:%[a-z0-9]+]] = zext i16 [[UF]] to i24
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i24 [[USA]], [[UF_EXT]]
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = lshr i24 [[SUM]], 8
+  // CHECK-NEXT: [[RES_TRUNC:%[a-z0-9]+]] = trunc i24 [[RES]] to i16
+  // CHECK-NEXT: store i16 [[RES_TRUNC]], i16* %usa, align 2
+  usa = usa - uf;
+}
+
+void IntSubtraction() {
+  // CHECK-LABEL: IntSubtraction
+  short _Accum sa;
+  _Accum a;
+  unsigned short _Accum usa;
+  _Sat short _Accum sa_sat;
+  int i;
+  unsigned int ui;
+  long _Fract lf;
+  _Bool b;
+
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[I:%[0-9]+]] = load i32, i32* %i, align 4
+  // CHECK-NEXT: [[SA_EXT:%[a-z0-9]+]] = sext i16 [[SA]] to i39
+  // CHECK-NEXT: [[I_EXT:%[a-z0-9]+]] = sext i32 [[I]] to i39
+  // CHECK-NEXT: [[I:%[a-z0-9]+]] = shl i39 [[I_EXT]], 7
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i39 [[SA_EXT]], [[I]]
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = trunc i39 [[SUM]] to i16
+  // CHECK-NEXT: store i16 [[RES]], i16* %sa, align 2
+  sa = sa - i;
+
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[UI:%[0-9]+]] = load i32, i32* %ui, align 4
+  // CHECK-NEXT: [[SA_EXT:%[a-z0-9]+]] = sext i16 [[SA]] to i40
+  // CHECK-NEXT: [[UI_EXT:%[a-z0-9]+]] = zext i32 [[UI]] to i40
+  // CHECK-NEXT: [[UI:%[a-z0-9]+]] = shl i40 [[UI_EXT]], 7
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i40 [[SA_EXT]], [[UI]]
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = trunc i40 [[SUM]] to i16
+  // CHECK-NEXT: store i16 [[RES]], i16* %sa, align 2
+  sa = sa - ui;
+
+  // CHECK:      [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[I:%[0-9]+]] = load i32, i32* %i, align 4
+  // SIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i40
+  // SIGNED-NEXT: [[I_EXT:%[a-z0-9]+]] = sext i32 [[I]] to i40
+  // SIGNED-NEXT: [[I:%[a-z0-9]+]] = shl i40 [[I_EXT]], 8
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = sub i40 [[USA_EXT]], [[I]]
+  // SIGNED-NEXT: [[RES:%[a-z0-9]+]] = trunc i40 [[SUM]] to i16
+  // UNSIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i39
+  // UNSIGNED-NEXT: [[I_EXT:%[a-z0-9]+]] = sext i32 [[I]] to i39
+  // UNSIGNED-NEXT: [[I:%[a-z0-9]+]] = shl i39 [[I_EXT]], 7
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = sub i39 [[USA_EXT]], [[I]]
+  // UNSIGNED-NEXT: [[RES:%[a-z0-9]+]] = trunc i39 [[SUM]] to i16
+  // CHECK-NEXT: store i16 [[RES]], i16* %usa, align 2
+  usa = usa - i;
+
+  // CHECK:      [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[I:%[0-9]+]] = load i32, i32* %ui, align 4
+  // SIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i40
+  // SIGNED-NEXT: [[I_EXT:%[a-z0-9]+]] = zext i32 [[I]] to i40
+  // SIGNED-NEXT: [[I:%[a-z0-9]+]] = shl i40 [[I_EXT]], 8
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = sub i40 [[USA_EXT]], [[I]]
+  // SIGNED-NEXT: [[RES:%[a-z0-9]+]] = trunc i40 [[SUM]] to i16
+  // UNSIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i39
+  // UNSIGNED-NEXT: [[I_EXT:%[a-z0-9]+]] = zext i32 [[I]] to i39
+  // UNSIGNED-NEXT: [[I:%[a-z0-9]+]] = shl i39 [[I_EXT]], 7
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = sub i39 [[USA_EXT]], [[I]]
+  // UNSIGNED-NEXT: [[RES:%[a-z0-9]+]] = trunc i39 [[SUM]] to i16
+  // CHECK-NEXT: store i16 [[RES]], i16* %usa, align 2
+  usa = usa - ui;
+
+  // CHECK:      [[LF:%[0-9]+]] = load i32, i32* %lf, align 4
+  // CHECK-NEXT: [[UI:%[0-9]+]] = load i32, i32* %ui, align 4
+  // CHECK-NEXT: [[LF_EXT:%[a-z0-9]+]] = sext i32 [[LF]] to i64
+  // CHECK-NEXT: [[UI_EXT:%[a-z0-9]+]] = zext i32 [[UI]] to i64
+  // CHECK-NEXT: [[UI:%[a-z0-9]+]] = shl i64 [[UI_EXT]], 31
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i64 [[LF_EXT]], [[UI]]
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = trunc i64 [[SUM]] to i32
+  // CHECK-NEXT: store i32 [[RES]], i32* %lf, align 4
+  lf = lf - ui;
+
+  // CHECK:      [[ACCUM:%[0-9]+]] = load i32, i32* %a, align 4
+  // CHECK-NEXT: [[BOOL:%[0-9]+]] = load i8, i8* %b, align 1
+  // CHECK-NEXT: [[AS_BOOL:%[a-z0-9]+]] = trunc i8 [[BOOL]] to i1
+  // CHECK-NEXT: [[BOOL_EXT:%[a-z0-9]+]] = zext i1 [[AS_BOOL]] to i32
+  // CHECK-NEXT: [[ACCUM_EXT:%[a-z0-9]+]] = sext i32 [[ACCUM]] to i47
+  // CHECK-NEXT: [[BOOL:%[a-z0-9]+]] = sext i32 [[BOOL_EXT]] to i47
+  // CHECK-NEXT: [[BOOL_EXT:%[a-z0-9]+]] = shl i47 [[BOOL]], 15
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = sub i47 [[ACCUM_EXT]], [[BOOL_EXT]]
+  // CHECK-NEXT: [[RESULT:%[a-z0-9]+]] = trunc i47 [[SUM]] to i32
+  // CHECK-NEXT: store i32 [[RESULT]], i32* %a, align 4
+  a = a - b;
+}
+
+void SaturatedSubtraction() {
+  // CHECK-LABEL: SaturatedSubtraction
+  short _Accum sa;
+  _Accum a;
+  long _Accum la;
+  unsigned short _Accum usa;
+  unsigned _Accum ua;
+  unsigned long _Accum ula;
+
+  _Sat short _Accum sa_sat;
+  _Sat _Accum a_sat;
+  _Sat long _Accum la_sat;
+  _Sat unsigned short _Accum usa_sat;
+  _Sat unsigned _Accum ua_sat;
+  _Sat unsigned long _Accum ula_sat;
+  _Sat unsigned _Fract uf_sat;
+
+  int i;
+  unsigned int ui;
+
+  // CHECK:      [[SA:%[0-9]+]] = load i16, i16* %sa, align 2
+  // CHECK-NEXT: [[SA_SAT:%[0-9]+]] = load i16, i16* %sa_sat, align 2
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = call i16 @llvm.ssub.sat.i16(i16 [[SA]], i16
+  // [[SA_SAT]])
+  // CHECK-NEXT: store i16 [[SUM]], i16* %sa_sat, align 2
+  sa_sat = sa - sa_sat;
+
+  // CHECK:      [[USA:%[0-9]+]] = load i16, i16* %usa, align 2
+  // CHECK-NEXT: [[USA_SAT:%[0-9]+]] = load i16, i16* %usa_sat, align 2
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = call i16 @llvm.usub.sat.i16(i16 [[USA]], i16 [[USA_SAT]])
+  // SIGNED-NEXT: store i16 [[SUM]], i16* %usa_sat, align 2
+  // UNSIGNED-NEXT: [[USA_TRUNC:%[a-z0-9]+]] = trunc i16 [[USA]] to i15
+  // UNSIGNED-NEXT: [[USA_SAT_TRUNC:%[a-z0-9]+]] = trunc i16 [[USA_SAT]] to i15
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = call i15 @llvm.usub.sat.i15(i15 [[USA_TRUNC]], i15 [[USA_SAT_TRUNC]])
+  // UNSIGNED-NEXT: [[SUM_EXT:%[a-z0-9]+]] = zext i15 [[SUM]] to i16
+  // UNSIGNED-NEXT: store i16 [[SUM_EXT]], i16* %usa_sat, align 2
+  usa_sat = usa - usa_sat;
+
+  // CHECK:      [[UA:%[0-9]+]] = load i32, i32* %ua, align 4
+  // CHECK-NEXT: [[USA:%[0-9]+]] = load i16, i16* %usa_sat, align 2
+  // SIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i32
+  // SIGNED-NEXT: [[USA:%[a-z0-9]+]] = shl i32 [[USA_EXT]], 8
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = call i32 @llvm.usub.sat.i32(i32 [[UA]], i32 [[USA]])
+  // SIGNED-NEXT: store i32 [[SUM]], i32* %ua_sat, align 4
+  // UNSIGNED-NEXT: [[UA_TRUNC:%[a-z0-9]+]] = trunc i32 [[UA]] to i31
+  // UNSIGNED-NEXT: [[USA_EXT:%[a-z0-9]+]] = zext i16 [[USA]] to i31
+  // UNSIGNED-NEXT: [[USA:%[a-z0-9]+]] = shl i31 [[USA_EXT]], 8
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = call i31 @llvm.usub.sat.i31(i31 [[UA_TRUNC]], i31 [[USA]])
+  // UNSIGNED-NEXT: [[SUM_EXT:%[a-z0-9]+]] = zext i31 [[SUM]] to i32
+  // UNSIGNED-NEXT: store i32 [[SUM_EXT]], i32* %ua_sat, align 4
+  ua_sat = ua - usa_sat;
+
+  // CHECK:      [[SA_SAT:%[0-9]+]] = load i16, i16* %sa_sat, align 2
+  // CHECK-NEXT: [[I:%[0-9]+]] = load i32, i32* %i, align 4
+  // CHECK-NEXT: [[SA_SAT_EXT:%[a-z0-9]+]] = sext i16 [[SA_SAT]] to i39
+  // CHECK-NEXT: [[I_EXT:%[a-z0-9]+]] = sext i32 [[I]] to i39
+  // CHECK-NEXT: [[I:%[a-z0-9]+]] = shl i39 [[I_EXT]], 7
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = call i39 @llvm.ssub.sat.i39(i39 [[SA_SAT_EXT]], i39 [[I]])
+  // CHECK-NEXT: [[USE_MAX:%[0-9]+]] = icmp sgt i39 [[SUM]], 32767
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = select i1 [[USE_MAX]], i39 32767, i39 [[SUM]]
+  // CHECK-NEXT: [[USE_MIN:%[0-9]+]] = icmp slt i39 [[RES]], -32768
+  // CHECK-NEXT: [[RES2:%[a-z0-9]+]] = select i1 [[USE_MIN]], i39 -32768, i39 [[RES]]
+  // CHECK-NEXT: [[RES3:%[a-z0-9]+]] = trunc i39 [[RES2]] to i16
+  // CHECK-NEXT: store i16 [[RES3]], i16* %sa_sat, align 2
+  sa_sat = sa_sat - i;
+
+  // CHECK:      [[SA_SAT:%[0-9]+]] = load i16, i16* %sa_sat, align 2
+  // CHECK-NEXT: [[I:%[0-9]+]] = load i32, i32* %ui, align 4
+  // CHECK-NEXT: [[SA_SAT_EXT:%[a-z0-9]+]] = sext i16 [[SA_SAT]] to i40
+  // CHECK-NEXT: [[I_EXT:%[a-z0-9]+]] = zext i32 [[I]] to i40
+  // CHECK-NEXT: [[I:%[a-z0-9]+]] = shl i40 [[I_EXT]], 7
+  // CHECK-NEXT: [[SUM:%[0-9]+]] = call i40 @llvm.ssub.sat.i40(i40 [[SA_SAT_EXT]], i40 [[I]])
+  // CHECK-NEXT: [[USE_MAX:%[0-9]+]] = icmp sgt i40 [[SUM]], 32767
+  // CHECK-NEXT: [[RES:%[a-z0-9]+]] = select i1 [[USE_MAX]], i40 32767, i40 [[SUM]]
+  // CHECK-NEXT: [[USE_MIN:%[0-9]+]] = icmp slt i40 [[RES]], -32768
+  // CHECK-NEXT: [[RES2:%[a-z0-9]+]] = select i1 [[USE_MIN]], i40 -32768, i40 [[RES]]
+  // CHECK-NEXT: [[RES3:%[a-z0-9]+]] = trunc i40 [[RES2]] to i16
+  // CHECK-NEXT: store i16 [[RES3]], i16* %sa_sat, align 2
+  sa_sat = sa_sat - ui;
+
+  // CHECK:      [[UF_SAT:%[0-9]+]] = load i16, i16* %uf_sat, align 2
+  // CHECK-NEXT: [[UF_SAT2:%[0-9]+]] = load i16, i16* %uf_sat, align 2
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = call i16 @llvm.usub.sat.i16(i16 [[UF_SAT]], i16 [[UF_SAT2]])
+  // SIGNED-NEXT: store i16 [[SUM]], i16* %uf_sat, align 2
+  // UNSIGNED-NEXT: [[UF_SAT_TRUNC:%[a-z0-9]+]] = trunc i16 [[UF_SAT]] to i15
+  // UNSIGNED-NEXT: [[UF_SAT_TRUNC2:%[a-z0-9]+]] = trunc i16 [[UF_SAT2]] to i15
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = call i15 @llvm.usub.sat.i15(i15 [[UF_SAT_TRUNC]], i15 [[UF_SAT_TRUNC2]])
+  // UNSIGNED-NEXT: [[SUM_EXT:%[a-z0-9]+]] = zext i15 [[SUM]] to i16
+  // UNSIGNED-NEXT: store i16 [[SUM_EXT]], i16* %uf_sat, align 2
+  uf_sat = uf_sat - uf_sat;
+
+  // CHECK:      [[USA_SAT:%[0-9]+]] = load i16, i16* %usa_sat, align 2
+  // CHECK-NEXT: [[I:%[0-9]+]] = load i32, i32* %i, align 4
+  // SIGNED-NEXT: [[USA_SAT_RESIZE:%[a-z0-9]+]] = zext i16 [[USA_SAT]] to i40
+  // SIGNED-NEXT: [[I_RESIZE:%[a-z0-9]+]] = sext i32 [[I]] to i40
+  // SIGNED-NEXT: [[I_UPSCALE:%[a-z0-9]+]] = shl i40 [[I_RESIZE]], 8
+  // SIGNED-NEXT: [[SUM:%[0-9]+]] = call i40 @llvm.usub.sat.i40(i40 [[USA_SAT_RESIZE]], i40 [[I_UPSCALE]])
+  // SIGNED-NEXT: [[USE_MAX:%[0-9]+]] = icmp sgt i40 [[SUM]], 65535
+  // SIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = select i1 [[USE_MAX]], i40 65535, i40 [[SUM]]
+  // SIGNED-NEXT: [[USE_MIN:%[0-9]+]] = icmp slt i40 [[RESULT]], 0
+  // SIGNED-NEXT: [[RESULT2:%[a-z0-9]+]] = select i1 [[USE_MIN]], i40 0, i40 [[RESULT]]
+  // SIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = trunc i40 [[RESULT2]] to i16
+  // UNSIGNED-NEXT: [[USA_SAT_RESIZE:%[a-z0-9]+]] = zext i16 [[USA_SAT]] to i39
+  // UNSIGNED-NEXT: [[I_RESIZE:%[a-z0-9]+]] = sext i32 [[I]] to i39
+  // UNSIGNED-NEXT: [[I_UPSCALE:%[a-z0-9]+]] = shl i39 [[I_RESIZE]], 7
+  // UNSIGNED-NEXT: [[SUM:%[0-9]+]] = call i39 @llvm.usub.sat.i39(i39 [[USA_SAT_RESIZE]], i39 [[I_UPSCALE]])
+  // UNSIGNED-NEXT: [[USE_MAX:%[0-9]+]] = icmp sgt i39 [[SUM]], 32767
+  // UNSIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = select i1 [[USE_MAX]], i39 32767, i39 [[SUM]]
+  // UNSIGNED-NEXT: [[USE_MIN:%[0-9]+]] = icmp slt i39 [[RESULT]], 0
+  // UNSIGNED-NEXT: [[RESULT2:%[a-z0-9]+]] = select i1 [[USE_MIN]], i39 0, i39 [[RESULT]]
+  // UNSIGNED-NEXT: [[RESULT:%[a-z0-9]+]] = trunc i39 [[RESULT2]] to i16
+  // CHECK-NEXT: store i16 [[RESULT]], i16* %usa_sat, align 2
+  usa_sat = usa_sat - i;
+}