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InstCombine: Simplify (A ^ B) or/and (A ^ B ^ C)
While we can already transform A | (A ^ B) into A | B, things get bad once we have (A ^ B) | (A ^ B ^ Cst) because reassociation will morph this into (A ^ B) | ((A ^ Cst) ^ B). Our existing patterns fail once this happens. To fix this, we add a new pattern which looks through the tree of xor binary operators to see that, in fact, there exists a redundant xor operation. What follows bellow is a correctness proof of the transform using CVC3. $ cat t.cvc A, B, C : BITVECTOR(64); QUERY BVXOR(A, B) | BVXOR(BVXOR(B, C), A) = BVXOR(A, B) | C; QUERY BVXOR(BVXOR(A, C), B) | BVXOR(A, B) = BVXOR(A, B) | C; QUERY BVXOR(A, B) & BVXOR(BVXOR(B, C), A) = BVXOR(A, B) & ~C; QUERY BVXOR(BVXOR(A, C), B) & BVXOR(A, B) = BVXOR(A, B) & ~C; $ cvc3 < t.cvc Valid. Valid. Valid. Valid. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214342 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -1283,6 +1283,18 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
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if (match(Op1, m_Or(m_Not(m_Specific(Op0)), m_Value(A))) ||
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match(Op1, m_Or(m_Value(A), m_Not(m_Specific(Op0)))))
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return BinaryOperator::CreateAnd(A, Op0);
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// (A ^ B) & ((B ^ C) ^ A) -> (A ^ B) & ~C
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if (match(Op0, m_Xor(m_Value(A), m_Value(B))))
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if (match(Op1, m_Xor(m_Xor(m_Specific(B), m_Value(C)), m_Specific(A))))
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if (Op1->hasOneUse() || cast<BinaryOperator>(Op1)->hasOneUse())
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return BinaryOperator::CreateAnd(Op0, Builder->CreateNot(C));
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// ((A ^ C) ^ B) & (B ^ A) -> (B ^ A) & ~C
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if (match(Op0, m_Xor(m_Xor(m_Value(A), m_Value(C)), m_Value(B))))
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if (match(Op1, m_Xor(m_Specific(B), m_Specific(A))))
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if (Op0->hasOneUse() || cast<BinaryOperator>(Op0)->hasOneUse())
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return BinaryOperator::CreateAnd(Op1, Builder->CreateNot(C));
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}
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if (ICmpInst *RHS = dyn_cast<ICmpInst>(Op1))
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@ -2080,6 +2092,18 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
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}
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}
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// (A ^ B) | ((B ^ C) ^ A) -> (A ^ B) | C
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if (match(Op0, m_Xor(m_Value(A), m_Value(B))))
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if (match(Op1, m_Xor(m_Xor(m_Specific(B), m_Value(C)), m_Specific(A))))
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if (Op1->hasOneUse() || cast<BinaryOperator>(Op1)->hasOneUse())
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return BinaryOperator::CreateOr(Op0, C);
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// ((A ^ C) ^ B) | (B ^ A) -> (B ^ A) | C
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if (match(Op0, m_Xor(m_Xor(m_Value(A), m_Value(C)), m_Value(B))))
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if (match(Op1, m_Xor(m_Specific(B), m_Specific(A))))
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if (Op0->hasOneUse() || cast<BinaryOperator>(Op0)->hasOneUse())
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return BinaryOperator::CreateOr(Op1, C);
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// (X >> Z) | (Y >> Z) -> (X|Y) >> Z for all shifts.
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if (BinaryOperator *SI1 = dyn_cast<BinaryOperator>(Op1)) {
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if (BinaryOperator *SI0 = dyn_cast<BinaryOperator>(Op0))
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@ -92,3 +92,23 @@ define i32 @test9(i32 %x, i32 %y) nounwind {
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; CHECK-NEXT: %z = or i32 %y.not, %x
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; CHECK-NEXT: ret i32 %z
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}
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define i32 @test10(i32 %A, i32 %B) {
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%xor1 = xor i32 %B, %A
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%not = xor i32 %A, -1
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%xor2 = xor i32 %not, %B
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%or = or i32 %xor1, %xor2
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ret i32 %or
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; CHECK-LABEL: @test10(
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; CHECK-NEXT: ret i32 -1
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}
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define i32 @test11(i32 %A, i32 %B) {
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%xor1 = xor i32 %B, %A
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%not = xor i32 %A, -1
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%xor2 = xor i32 %not, %B
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%or = or i32 %xor1, %xor2
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ret i32 %or
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; CHECK-LABEL: @test11(
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; CHECK-NEXT: ret i32 -1
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}
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@ -125,3 +125,23 @@ define i32 @test10(i32 %b, i32 %c) {
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; CHECK-LABEL: @test10(
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; CHECK-NEXT: %xor2 = or i32 %b, %c
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}
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define i32 @test11(i32 %A, i32 %B) {
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%xor1 = xor i32 %B, %A
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%not = xor i32 %A, -1
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%xor2 = xor i32 %not, %B
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%and = and i32 %xor1, %xor2
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ret i32 %and
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; CHECK-LABEL: @test11(
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; CHECK-NEXT: ret i32 0
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}
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define i32 @test12(i32 %A, i32 %B) {
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%xor1 = xor i32 %B, %A
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%not = xor i32 %A, -1
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%xor2 = xor i32 %not, %B
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%and = and i32 %xor1, %xor2
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ret i32 %and
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; CHECK-LABEL: @test12(
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; CHECK-NEXT: ret i32 0
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}
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