Make APInt::countLeadingZerosSlowCase() treat the contents of padding bits
as undefined. Fixes an assertion in APFloat::toString noticed by Dale.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95196 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/APInt.cpp b/lib/Support/APInt.cpp
index 9d14684..f41b31a 100644
--- a/lib/Support/APInt.cpp
+++ b/lib/Support/APInt.cpp
@@ -767,8 +767,23 @@
}
unsigned APInt::countLeadingZerosSlowCase() const {
- unsigned Count = 0;
- for (unsigned i = getNumWords(); i > 0u; --i) {
+ // Treat the most significand word differently because it might have
+ // meaningless bits set beyond the precision.
+ unsigned BitsInMSW = BitWidth % APINT_BITS_PER_WORD;
+ integerPart MSWMask;
+ if (BitsInMSW) MSWMask = (integerPart(1) << BitsInMSW) - 1;
+ else {
+ MSWMask = ~integerPart(0);
+ BitsInMSW = APINT_BITS_PER_WORD;
+ }
+
+ unsigned i = getNumWords();
+ integerPart MSW = pVal[i-1] & MSWMask;
+ if (MSW)
+ return CountLeadingZeros_64(MSW) - (APINT_BITS_PER_WORD - BitsInMSW);
+
+ unsigned Count = BitsInMSW;
+ for (--i; i > 0u; --i) {
if (pVal[i-1] == 0)
Count += APINT_BITS_PER_WORD;
else {
@@ -776,10 +791,7 @@
break;
}
}
- unsigned remainder = BitWidth % APINT_BITS_PER_WORD;
- if (remainder)
- Count -= APINT_BITS_PER_WORD - remainder;
- return std::min(Count, BitWidth);
+ return Count;
}
static unsigned countLeadingOnes_64(uint64_t V, unsigned skip) {