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Optimize (x/y)*y into x-(x%y) in general. Div and rem are about the same, and
a subtract is cheaper than a multiply. This generalizes an existing transform. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59800 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -2477,17 +2477,6 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
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Constant *CP1 = Subtract(ConstantInt::get(I.getType(), 1), C2);
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return BinaryOperator::CreateMul(Op0, CP1);
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}
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// X - ((X / Y) * Y) --> X % Y
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if (Op1I->getOpcode() == Instruction::Mul)
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if (Instruction *I = dyn_cast<Instruction>(Op1I->getOperand(0)))
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if (Op0 == I->getOperand(0) &&
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Op1I->getOperand(1) == I->getOperand(1)) {
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if (I->getOpcode() == Instruction::SDiv)
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return BinaryOperator::CreateSRem(Op0, Op1I->getOperand(1));
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if (I->getOpcode() == Instruction::UDiv)
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return BinaryOperator::CreateURem(Op0, Op1I->getOperand(1));
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}
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}
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}
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@ -2622,6 +2611,40 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
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if (Value *Op1v = dyn_castNegVal(I.getOperand(1)))
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return BinaryOperator::CreateMul(Op0v, Op1v);
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// (X / Y) * Y = X - (X % Y)
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// (X / Y) * -Y = (X % Y) - X
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{
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Value *Op1 = I.getOperand(1);
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BinaryOperator *BO = dyn_cast<BinaryOperator>(Op0);
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if (!BO ||
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(BO->getOpcode() != Instruction::UDiv &&
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BO->getOpcode() != Instruction::SDiv)) {
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Op1 = Op0;
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BO = dyn_cast<BinaryOperator>(I.getOperand(1));
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}
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Value *Neg = dyn_castNegVal(Op1);
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if (BO && BO->hasOneUse() &&
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(BO->getOperand(1) == Op1 || BO->getOperand(1) == Neg) &&
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(BO->getOpcode() == Instruction::UDiv ||
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BO->getOpcode() == Instruction::SDiv)) {
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Value *Op0BO = BO->getOperand(0), *Op1BO = BO->getOperand(1);
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Instruction *Rem;
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if (BO->getOpcode() == Instruction::UDiv)
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Rem = BinaryOperator::CreateURem(Op0BO, Op1BO);
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else
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Rem = BinaryOperator::CreateSRem(Op0BO, Op1BO);
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InsertNewInstBefore(Rem, I);
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Rem->takeName(BO);
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if (Op1BO == Op1)
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return BinaryOperator::CreateSub(Op0BO, Rem);
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else
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return BinaryOperator::CreateSub(Rem, Op0BO);
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}
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}
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if (I.getType() == Type::Int1Ty)
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return BinaryOperator::CreateAnd(Op0, I.getOperand(1));
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34
test/Transforms/InstCombine/2008-11-20-DivMulRem.ll
Normal file
34
test/Transforms/InstCombine/2008-11-20-DivMulRem.ll
Normal file
@ -0,0 +1,34 @@
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; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t
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; RUN: grep urem %t | count 3
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; RUN: grep srem %t | count 1
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; RUN: grep sub %t | count 2
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; RUN: grep add %t | count 1
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; PR3103
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define i8 @test1(i8 %x, i8 %y) {
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%A = udiv i8 %x, %y
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%B = mul i8 %A, %y
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%C = sub i8 %x, %B
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ret i8 %C
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}
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define i8 @test2(i8 %x, i8 %y) {
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%A = sdiv i8 %x, %y
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%B = mul i8 %A, %y
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%C = sub i8 %x, %B
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ret i8 %C
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}
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define i8 @test3(i8 %x, i8 %y) {
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%A = udiv i8 %x, %y
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%B = mul i8 %A, %y
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%C = sub i8 %B, %x
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ret i8 %C
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}
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define i8 @test4(i8 %x) {
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%A = udiv i8 %x, 3
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%B = mul i8 %A, -3
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%C = sub i8 %x, %B
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ret i8 %C
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}
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