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Added instruction combine to transform few more negative values addition to subtraction (Part 1)

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This patch enables transforms for following patterns.
  (x + (~(y & c) + 1)   -->   x - (y & c)
  (x + (~((y >> z) & c) + 1)   -->   x - ((y>>z) & c)

Differential Revision: http://reviews.llvm.org/D3733



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211266 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dinesh Dwivedi
2014-06-19 10:36:52 +00:00
parent cfdf805286
commit 85386a3de9
2 changed files with 108 additions and 0 deletions
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45
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@@ -954,6 +954,48 @@ bool InstCombiner::WillNotOverflowUnsignedAdd(Value *LHS, Value *RHS) {
return true;
return false;
}
// Checks if any operand is negative and we can convert add to sub.
// This function checks for following negative patterns
// ADD(XOR(OR(Z, NOT(C)), C)), 1) == NEG(AND(Z, C))
// TODO: ADD(XOR(AND(Z, ~C), ~C), 1) == NEG(OR(Z, C)) if C is even
// TODO: XOR(AND(Z, ~C), (~C + 1)) == NEG(OR(Z, C)) if C is odd
Value *checkForNegativeOperand(BinaryOperator &I,
InstCombiner::BuilderTy *Builder) {
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
// This function creates 2 instructions to replace ADD, we need at least one
// of LHS or RHS to have one use to ensure benefit in transform.
if (!LHS->hasOneUse() && !RHS->hasOneUse())
return nullptr;
bool IHasNSW = I.hasNoSignedWrap();
bool IHasNUW = I.hasNoUnsignedWrap();
Value *X = nullptr, *Y = nullptr, *Z = nullptr;
const APInt *C1 = nullptr, *C2 = nullptr;
// if ONE is on other side, swap
if (match(RHS, m_Add(m_Value(X), m_One())))
std::swap(LHS, RHS);
if (match(LHS, m_Add(m_Value(X), m_One()))) {
// if XOR on other side, swap
if (match(RHS, m_Xor(m_Value(Y), m_APInt(C1))))
std::swap(X, RHS);
// X = XOR(Y, C1), Y = OR(Z, C2), C2 = NOT(C1) ==> X == NOT(AND(Z, C1))
// ADD(ADD(X, 1), RHS) == ADD(X, ADD(RHS, 1)) == SUB(RHS, AND(Z, C1))
if (match(X, m_Xor(m_Value(Y), m_APInt(C1)))) {
if (match(Y, m_Or(m_Value(Z), m_APInt(C2))) && (*C2 == ~(*C1))) {
Value *NewAnd = Builder->CreateAnd(Z, *C1);
return Builder->CreateSub(RHS, NewAnd, "", IHasNUW, IHasNSW);
}
}
}
return nullptr;
}
Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
@@ -1065,6 +1107,9 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
if (Value *V = dyn_castNegVal(RHS))
return BinaryOperator::CreateSub(LHS, V);
if (Value *V = checkForNegativeOperand(I, Builder))
return ReplaceInstUsesWith(I, V);
// A+B --> A|B iff A and B have no bits set in common.
if (IntegerType *IT = dyn_cast<IntegerType>(I.getType())) {
APInt LHSKnownOne(IT->getBitWidth(), 0);