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isKnownToBeAPowerOfTwo: Strengthen isKnownToBeAPowerOfTwo's analysis on add instructions

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Call into ComputeMaskedBits to figure out which bits are set on both add
operands and determine if the value is a power-of-two-or-zero or not.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187445 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2013-07-30 21:01:36 +00:00
parent f34dc428fa
commit 36850ad779
2 changed files with 62 additions and 16 deletions
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46
lib/Analysis/ValueTracking.cpp
View File

@ -855,22 +855,36 @@ bool llvm::isKnownToBeAPowerOfTwo(Value *V, bool OrZero, unsigned Depth) {
return false;
}
if (match(V, m_Add(m_Value(X), m_Value(Y))))
if (OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V))
if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
// Adding a power of two to the same power of two is a power of two or
// zero.
if (BinaryOperator *XBO = dyn_cast<BinaryOperator>(X))
if (XBO->getOpcode() == Instruction::And)
if (XBO->getOperand(0) == Y || XBO->getOperand(1) == Y)
if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
return true;
if (BinaryOperator *YBO = dyn_cast<BinaryOperator>(Y))
if (YBO->getOpcode() == Instruction::And)
if (YBO->getOperand(0) == X || YBO->getOperand(1) == X)
if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
return true;
}
// Adding a power-of-two or zero to the same power-of-two or zero yields
// either the original power-of-two, a larger power-of-two or zero.
if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
if (match(X, m_And(m_Specific(Y), m_Value())) ||
match(X, m_And(m_Value(), m_Specific(Y))))
if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth))
return true;
if (match(Y, m_And(m_Specific(X), m_Value())) ||
match(Y, m_And(m_Value(), m_Specific(X))))
if (isKnownToBeAPowerOfTwo(X, OrZero, Depth))
return true;
unsigned BitWidth = V->getType()->getScalarSizeInBits();
APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
ComputeMaskedBits(X, LHSZeroBits, LHSOneBits, 0, Depth);
APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
ComputeMaskedBits(Y, RHSZeroBits, RHSOneBits, 0, Depth);
// If i8 V is a power of two or zero:
// ZeroBits: 1 1 1 0 1 1 1 1
// ~ZeroBits: 0 0 0 1 0 0 0 0
if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
// If OrZero isn't set, we cannot give back a zero result.
// Make sure either the LHS or RHS has a bit set.
if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
return true;
}
}
// 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

32
test/Transforms/InstCombine/rem.ll
View File

@ -172,3 +172,35 @@ define i32 @test17(i32 %X) {
%A = urem i32 1, %X
ret i32 %A
}
define i32 @test18(i16 %x, i32 %y) {
; CHECK: @test18
; 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
}
define i32 @test19(i32 %x, i32 %y) {
; CHECK: @test19
; CHECK-NEXT: [[SHL1:%.*]] = shl i32 1, %x
; CHECK-NEXT: [[SHL2:%.*]] = shl i32 1, %y
; CHECK-NEXT: [[AND:%.*]] = and i32 [[SHL1]], [[SHL2]]
; CHECK-NEXT: [[ADD:%.*]] = add i32 [[AND]], [[SHL1]]
; CHECK-NEXT: [[SUB:%.*]] = add i32 [[ADD]], -1
; CHECK-NEXT: [[REM:%.*]] = and i32 [[SUB]], %y
; CHECK-NEXT: ret i32 [[REM]]
%A = shl i32 1, %x
%B = shl i32 1, %y
%C = and i32 %A, %B
%D = add i32 %C, %A
%E = urem i32 %y, %D
ret i32 %E
}