Even if we don't have any known bits, we can assume that there is
at least 1 sign bit. This is consistent with ComputeNumSignBits
which always returns at least 1.
Add KnownBits::countMaxSignedBits() which computes the number of
bits needed to represent all signed values with those known bits.
This is the signed equivalent of countMaxActiveBits().
Split from D116469.
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D116500
return countMinLeadingZeros();
if (isNegative())
return countMinLeadingOnes();
- return 0;
+ // Every value has at least 1 sign bit.
+ return 1;
+ }
+
+ /// Returns the maximum number of bits needed to represent all possible
+ /// signed values with these known bits.
+ unsigned countMaxSignedBits() const {
+ return getBitWidth() - countMinSignBits() + 1;
}
/// Returns the maximum number of trailing zero bits possible.
});
}
+TEST(KnownBitsTest, CountMaxSignedBits) {
+ unsigned Bits = 4;
+ ForeachKnownBits(Bits, [&](const KnownBits &Known) {
+ unsigned Expected = 0;
+ ForeachNumInKnownBits(Known, [&](const APInt &N) {
+ Expected = std::max(Expected, N.getMinSignedBits());
+ });
+ EXPECT_EQ(Expected, Known.countMaxSignedBits());
+ });
+}
+
TEST(KnownBitsTest, SExtOrTrunc) {
const unsigned NarrowerSize = 4;
const unsigned BaseSize = 6;