// code.
if (!V->hasOneUse()) return 0;
+ bool MadeChange = false;
+
// ((1 << A) >>u B) --> (1 << (A-B))
// Because V cannot be zero, we know that B is less than A.
- Value *A = 0, *B = 0; ConstantInt *One = 0;
- if (match(V, m_LShr(m_OneUse(m_Shl(m_ConstantInt(One), m_Value(A))),
+ Value *A = 0, *B = 0, *PowerOf2 = 0;
+ if (match(V, m_LShr(m_OneUse(m_Shl(m_Value(PowerOf2), m_Value(A))),
m_Value(B))) &&
// The "1" can be any value known to be a power of 2.
- One->getValue().isPowerOf2()) {
+ isPowerOfTwo(PowerOf2, IC.getTargetData())) {
A = IC.Builder->CreateSub(A, B, "tmp");
- return IC.Builder->CreateShl(One, A);
+ return IC.Builder->CreateShl(PowerOf2, A);
}
+ // (PowerOfTwo >>u B) --> isExact since shifting out the result would make it
+ // inexact. Similarly for <<.
+ if (BinaryOperator *I = dyn_cast<BinaryOperator>(V))
+ if (I->isLogicalShift() &&
+ isPowerOfTwo(I->getOperand(0), IC.getTargetData())) {
+ // We know that this is an exact/nuw shift and that the input is a
+ // non-zero context as well.
+ if (Value *V2 = simplifyValueKnownNonZero(I->getOperand(0), IC)) {
+ I->setOperand(0, V2);
+ MadeChange = true;
+ }
+
+ if (I->getOpcode() == Instruction::LShr && !I->isExact()) {
+ I->setIsExact();
+ MadeChange = true;
+ }
+
+ if (I->getOpcode() == Instruction::Shl && !I->hasNoUnsignedWrap()) {
+ I->setHasNoUnsignedWrap();
+ MadeChange = true;
+ }
+ }
+
// TODO: Lots more we could do here:
- // "1 >> X" could get an "isexact" bit.
// If V is a phi node, we can call this on each of its operands.
// "select cond, X, 0" can simplify to "X".
- return 0;
+ return MadeChange ? V : 0;
}
return BinaryOperator::CreateAdd(Add, Builder->CreateMul(C1, CI));
}
}
+
+ // (Y - X) * (-(2**n)) -> (X - Y) * (2**n), for positive nonzero n
+ // (Y + const) * (-(2**n)) -> (-constY) * (2**n), for positive nonzero n
+ // The "* (2**n)" thus becomes a potential shifting opportunity.
+ {
+ const APInt & Val = CI->getValue();
+ const APInt &PosVal = Val.abs();
+ if (Val.isNegative() && PosVal.isPowerOf2()) {
+ Value *X = 0, *Y = 0;
+ if (Op0->hasOneUse()) {
+ ConstantInt *C1;
+ Value *Sub = 0;
+ if (match(Op0, m_Sub(m_Value(Y), m_Value(X))))
+ Sub = Builder->CreateSub(X, Y, "suba");
+ else if (match(Op0, m_Add(m_Value(Y), m_ConstantInt(C1))))
+ Sub = Builder->CreateSub(Builder->CreateNeg(C1), Y, "subc");
+ if (Sub)
+ return
+ BinaryOperator::CreateMul(Sub,
+ ConstantInt::get(Y->getType(), PosVal));
+ }
+ }
+ }
}
// Simplify mul instructions with a constant RHS.