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InstCombine: Simplify (A ^ B) or/and (A ^ B ^ C)

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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
This commit is contained in:
David Majnemer 2014-07-30 21:26:37 +00:00
parent ee6a05091a
commit 5624046453
3 changed files with 64 additions and 0 deletions
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24
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1283,6 +1283,18 @@ Instruction *InstCombiner::visitAnd(BinaryOperator &I) {
if (match(Op1, m_Or(m_Not(m_Specific(Op0)), m_Value(A))) ||
match(Op1, m_Or(m_Value(A), m_Not(m_Specific(Op0)))))
return BinaryOperator::CreateAnd(A, Op0);
// (A ^ B) & ((B ^ C) ^ A) -> (A ^ B) & ~C
if (match(Op0, m_Xor(m_Value(A), m_Value(B))))
if (match(Op1, m_Xor(m_Xor(m_Specific(B), m_Value(C)), m_Specific(A))))
if (Op1->hasOneUse() || cast<BinaryOperator>(Op1)->hasOneUse())
return BinaryOperator::CreateAnd(Op0, Builder->CreateNot(C));
// ((A ^ C) ^ B) & (B ^ A) -> (B ^ A) & ~C
if (match(Op0, m_Xor(m_Xor(m_Value(A), m_Value(C)), m_Value(B))))
if (match(Op1, m_Xor(m_Specific(B), m_Specific(A))))
if (Op0->hasOneUse() || cast<BinaryOperator>(Op0)->hasOneUse())
return BinaryOperator::CreateAnd(Op1, Builder->CreateNot(C));
}
if (ICmpInst *RHS = dyn_cast<ICmpInst>(Op1))
@ -2080,6 +2092,18 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
}
}
// (A ^ B) | ((B ^ C) ^ A) -> (A ^ B) | C
if (match(Op0, m_Xor(m_Value(A), m_Value(B))))
if (match(Op1, m_Xor(m_Xor(m_Specific(B), m_Value(C)), m_Specific(A))))
if (Op1->hasOneUse() || cast<BinaryOperator>(Op1)->hasOneUse())
return BinaryOperator::CreateOr(Op0, C);
// ((A ^ C) ^ B) | (B ^ A) -> (B ^ A) | C
if (match(Op0, m_Xor(m_Xor(m_Value(A), m_Value(C)), m_Value(B))))
if (match(Op1, m_Xor(m_Specific(B), m_Specific(A))))
if (Op0->hasOneUse() || cast<BinaryOperator>(Op0)->hasOneUse())
return BinaryOperator::CreateOr(Op1, C);
// (X >> Z) | (Y >> Z) -> (X|Y) >> Z for all shifts.
if (BinaryOperator *SI1 = dyn_cast<BinaryOperator>(Op1)) {
if (BinaryOperator *SI0 = dyn_cast<BinaryOperator>(Op0))

20
test/Transforms/InstCombine/or-xor.ll
View File

@ -92,3 +92,23 @@ define i32 @test9(i32 %x, i32 %y) nounwind {
; CHECK-NEXT: %z = or i32 %y.not, %x
; CHECK-NEXT: ret i32 %z
}
define i32 @test10(i32 %A, i32 %B) {
%xor1 = xor i32 %B, %A
%not = xor i32 %A, -1
%xor2 = xor i32 %not, %B
%or = or i32 %xor1, %xor2
ret i32 %or
; CHECK-LABEL: @test10(
; CHECK-NEXT: ret i32 -1
}
define i32 @test11(i32 %A, i32 %B) {
%xor1 = xor i32 %B, %A
%not = xor i32 %A, -1
%xor2 = xor i32 %not, %B
%or = or i32 %xor1, %xor2
ret i32 %or
; CHECK-LABEL: @test11(
; CHECK-NEXT: ret i32 -1
}

20
test/Transforms/InstCombine/xor2.ll
View File

@ -125,3 +125,23 @@ define i32 @test10(i32 %b, i32 %c) {
; CHECK-LABEL: @test10(
; CHECK-NEXT: %xor2 = or i32 %b, %c
}
define i32 @test11(i32 %A, i32 %B) {
%xor1 = xor i32 %B, %A
%not = xor i32 %A, -1
%xor2 = xor i32 %not, %B
%and = and i32 %xor1, %xor2
ret i32 %and
; CHECK-LABEL: @test11(
; CHECK-NEXT: ret i32 0
}
define i32 @test12(i32 %A, i32 %B) {
%xor1 = xor i32 %B, %A
%not = xor i32 %A, -1
%xor2 = xor i32 %not, %B
%and = and i32 %xor1, %xor2
ret i32 %and
; CHECK-LABEL: @test12(
; CHECK-NEXT: ret i32 0
}