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Reduce x - y to -y when we know the 'x' part will get masked off anyways.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53271 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2008-07-09 04:32:37 +00:00
parent 97c2537269
commit b4d1bc989e
2 changed files with 21 additions and 1 deletions
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13
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -3461,6 +3461,17 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
// ((A ^ N) - B) & AndRHS -> (A - B) & AndRHS iff N&AndRHS == 0
if (Value *V = FoldLogicalPlusAnd(Op0LHS, Op0RHS, AndRHS, true, I))
return BinaryOperator::CreateAnd(V, AndRHS);
// (A - N) & AndRHS -> -N & AndRHS where A & AndRHS == 0
if (Op0I->hasOneUse() && MaskedValueIsZero(Op0LHS, AndRHSMask)) {
ConstantInt *A = dyn_cast<ConstantInt>(Op0LHS);
if (!A || !A->isZero()) {
Instruction *NewNeg = BinaryOperator::CreateNeg(Op0RHS);
InsertNewInstBefore(NewNeg, I);
return BinaryOperator::CreateAnd(NewNeg, AndRHS);
}
}
break;
}
@ -3780,7 +3791,7 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
}
}
}
return Changed ? &I : 0;
}

9
test/Transforms/InstCombine/2008-07-08-SubAnd.ll Normal file
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@ -0,0 +1,9 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep -v {i32 8}
; PR2330
define i32 @a(i32 %a) nounwind {
entry:
%tmp2 = sub i32 8, %a ; <i32> [#uses=1]
%tmp3 = and i32 %tmp2, 7 ; <i32> [#uses=1]
ret i32 %tmp3
}