+/// Match a sadd_sat or ssub_sat which is using min/max to clamp the value.
+Instruction *InstCombiner::matchSAddSubSat(SelectInst &MinMax1) {
+ Type *Ty = MinMax1.getType();
+
+ // We are looking for a tree of:
+ // max(INT_MIN, min(INT_MAX, add(sext(A), sext(B))))
+ // Where the min and max could be reversed
+ Instruction *MinMax2;
+ BinaryOperator *AddSub;
+ const APInt *MinValue, *MaxValue;
+ if (match(&MinMax1, m_SMin(m_Instruction(MinMax2), m_APInt(MaxValue)))) {
+ if (!match(MinMax2, m_SMax(m_BinOp(AddSub), m_APInt(MinValue))))
+ return nullptr;
+ } else if (match(&MinMax1,
+ m_SMax(m_Instruction(MinMax2), m_APInt(MinValue)))) {
+ if (!match(MinMax2, m_SMin(m_BinOp(AddSub), m_APInt(MaxValue))))
+ return nullptr;
+ } else
+ return nullptr;
+
+ // Check that the constants clamp a saturate, and that the new type would be
+ // sensible to convert to.
+ if (!(*MaxValue + 1).isPowerOf2() || -*MinValue != *MaxValue + 1)
+ return nullptr;
+ // In what bitwidth can this be treated as saturating arithmetics?
+ unsigned NewBitWidth = (*MaxValue + 1).logBase2() + 1;
+ // FIXME: This isn't quite right for vectors, but using the scalar type is a
+ // good first approximation for what should be done there.
+ if (!shouldChangeType(Ty->getScalarType()->getIntegerBitWidth(), NewBitWidth))
+ return nullptr;
+
+ // Also make sure that the number of uses is as expected. The "3"s are for the
+ // the two items of min/max (the compare and the select).
+ if (MinMax2->hasNUsesOrMore(3) || AddSub->hasNUsesOrMore(3))
+ return nullptr;
+
+ // Create the new type (which can be a vector type)
+ Type *NewTy = Ty->getWithNewBitWidth(NewBitWidth);
+ // Match the two extends from the add/sub
+ Value *A, *B;
+ if(!match(AddSub, m_BinOp(m_SExt(m_Value(A)), m_SExt(m_Value(B)))))
+ return nullptr;
+ // And check the incoming values are of a type smaller than or equal to the
+ // size of the saturation. Otherwise the higher bits can cause different
+ // results.
+ if (A->getType()->getScalarSizeInBits() > NewBitWidth ||
+ B->getType()->getScalarSizeInBits() > NewBitWidth)
+ return nullptr;
+
+ Intrinsic::ID IntrinsicID;
+ if (AddSub->getOpcode() == Instruction::Add)
+ IntrinsicID = Intrinsic::sadd_sat;
+ else if (AddSub->getOpcode() == Instruction::Sub)
+ IntrinsicID = Intrinsic::ssub_sat;
+ else
+ return nullptr;
+
+ // Finally create and return the sat intrinsic, truncated to the new type
+ Function *F = Intrinsic::getDeclaration(MinMax1.getModule(), IntrinsicID, NewTy);
+ Value *AT = Builder.CreateSExt(A, NewTy);
+ Value *BT = Builder.CreateSExt(B, NewTy);
+ Value *Sat = Builder.CreateCall(F, {AT, BT});
+ return CastInst::Create(Instruction::SExt, Sat, Ty);
+}
+
projects / llvm / commitdiff