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ValueTracking: Teach isKnownToBeAPowerOfTwo about (ADD X, (XOR X, Y)) where X is a power of two

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This allows us to simplify urem instructions involving the add+xor to
turn into simpler math.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185272 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2013-06-29 23:44:53 +00:00
parent bebf6222f6
commit 58b6dc032a
2 changed files with 33 additions and 10 deletions
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28
lib/Analysis/ValueTracking.cpp
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@ -855,16 +855,24 @@ bool llvm::isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth) {
return false; return false;
} }
// Adding a power of two to the same power of two is a power of two or zero. if (match(V, m_Add(m_Value(X), m_Value(Y))))
if (OrZero && match(V, m_Add(m_Value(X), m_Value(Y)))) { if (OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V))
if (match(X, m_And(m_Value(), m_Specific(Y)))) { if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
if (isKnownToBeAPowerOfTwo(Y, /*OrZero*/true, Depth)) // Adding a power of two to the same power of two is a power of two or
return true; // zero.
} else if (match(Y, m_And(m_Value(), m_Specific(X)))) { if (BinaryOperator *XBO = dyn_cast<BinaryOperator>(X))
if (isKnownToBeAPowerOfTwo(X, /*OrZero*/true, Depth)) if (XBO->getOpcode() == Instruction::And ||
return true; XBO->getOpcode() == Instruction::Xor)
} if (XBO->getOperand(0) == Y || XBO->getOperand(1) == Y)
} if (isKnownToBeAPowerOfTwo(Y, /*OrZero*/true, Depth))
return true;
if (BinaryOperator *YBO = dyn_cast<BinaryOperator>(Y))
if (YBO->getOpcode() == Instruction::And ||
YBO->getOpcode() == Instruction::Xor)
if (YBO->getOperand(0) == X || YBO->getOperand(1) == X)
if (isKnownToBeAPowerOfTwo(X, /*OrYero*/true, Depth))
return true;
}
// An exact divide or right shift can only shift off zero bits, so the result // An exact divide or right shift can only shift off zero bits, so the result
// is a power of two only if the first operand is a power of two and not // is a power of two only if the first operand is a power of two and not

15
test/Transforms/InstCombine/rem.ll
View File

@ -163,3 +163,18 @@ define i32 @test16(i32 %x, i32 %y) {
%rem = urem i32 %x, %add %rem = urem i32 %x, %add
ret i32 %rem ret i32 %rem
} }
define i32 @test17(i16 %x, i32 %y) {
; CHECK: @test17
; CHECK-NEXT: [[AND:%.*]] = and i16 %x, 4
; CHECK-NEXT: [[EXT:%.*]] = zext i16 [[AND]] to i32
; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i32 [[EXT]], 3
; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[SHL]], 63
; CHECK-NEXT: [[REM:%.*]] = and i32 [[XOR]], %y
; CHECK-NEXT: ret i32 [[REM]]
%1 = and i16 %x, 4
%2 = icmp ne i16 %1, 0
%3 = select i1 %2, i32 32, i32 64
%4 = urem i32 %y, %3
ret i32 %4
}