Teach value tracking to make use of flags in more situations.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126642 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index fac0407..70d51fa 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -696,6 +696,15 @@
return isPowerOfTwo(SI->getTrueValue(), TD, Depth) &&
isPowerOfTwo(SI->getFalseValue(), TD, Depth);
+ // An exact divide or right shift can only shift off zero bits, so the result
+ // is non-zero only if the first operand is non-zero.
+ if (match(V, m_Shr(m_Value(), m_Value())) ||
+ match(V, m_IDiv(m_Value(), m_Value()))) {
+ BinaryOperator *BO = cast<BinaryOperator>(V);
+ if (BO->isExact())
+ return isPowerOfTwo(BO->getOperand(0), TD, Depth);
+ }
+
return false;
}
@@ -732,6 +741,11 @@
// shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
// if the lowest bit is shifted off the end.
if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
+ // shl nuw can't remove any non-zero bits.
+ BinaryOperator *BO = cast<BinaryOperator>(V);
+ if (BO->hasNoUnsignedWrap())
+ return isKnownNonZero(X, TD, Depth);
+
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
ComputeMaskedBits(X, APInt(BitWidth, 1), KnownZero, KnownOne, TD, Depth);
@@ -741,11 +755,22 @@
// shr X, Y != 0 if X is negative. Note that the value of the shift is not
// defined if the sign bit is shifted off the end.
else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
+ // shr exact can only shift out zero bits.
+ BinaryOperator *BO = cast<BinaryOperator>(V);
+ if (BO->isExact())
+ return isKnownNonZero(X, TD, Depth);
+
bool XKnownNonNegative, XKnownNegative;
ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
if (XKnownNegative)
return true;
}
+ // div exact can only produce a zero if the dividend is zero.
+ else if (match(V, m_IDiv(m_Value(X), m_Value()))) {
+ BinaryOperator *BO = cast<BinaryOperator>(V);
+ if (BO->isExact())
+ return isKnownNonZero(X, TD, Depth);
+ }
// X + Y.
else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
bool XKnownNonNegative, XKnownNegative;