sorenj added a comment.
So, I ran this check against the cxx directory of llvm, it fired 5 times so
let's look at the context and disucss:
There are two identical spots in locale.cpp, the first is around line 2717
uint16_t t = static_cast<uint16_t>(
0xD800
| ((((wc & 0x1F0000) >> 16) - 1) << 6)
| ((wc & 0x00FC00) >> 10));
the fact that a signed value is being right shifted here surprises me, but
looking earlier there's a branch for wc < 0x010000 so we are safe here against
wc being 0. So this is a false diagnostic. Still, wc is a uint32_t, it's the
0x1f0000 that converts it to signed. Probably should be 0x1f0000u? Will still
false-alarm on this code though unless you use - 1u to make the whole thing
unsigned end to end.
the third is in memory.cc
void*
align(size_t alignment, size_t size, void*& ptr, size_t& space)
{
void* r = nullptr;
if (size <= space)
{
char* p1 = static_cast<char*>(ptr);
char* p2 = reinterpret_cast<char*>(reinterpret_cast<size_t>(p1 +
(alignment - 1)) & -alignment);
here it doesn't make sense for alignment to be zero, and the & -alignment will
be zero anyway, so false alarm although some check for alignment > 0 might be
an improvement
The last two are in valarray.cpp lines 35 and 43, I've copied a large excerpt
here
void
gslice::__init(size_t __start)
{
valarray<size_t> __indices(__size_.size());
size_t __k = __size_.size() != 0;
for (size_t __i = 0; __i < __size_.size(); ++__i)
__k *= __size_[__i];
__1d_.resize(__k);
if (__1d_.size())
{
__k = 0;
__1d_[__k] = __start;
while (true)
{
size_t __i = __indices.size() - 1;
while (true)
{
if (++__indices[__i] < __size_[__i])
{
++__k;
__1d_[__k] = __1d_[__k-1] + __stride_[__i];
for (size_t __j = __i + 1; __j != __indices.size(); ++__j)
__1d_[__k] -= __stride_[__j] * (__size_[__j] - 1);
break;
}
else
with some looking I can see that `__indices.size()` has to be non-zero. It's
less clear to me that `size_[__j]` is strictly positive here and there should
probably be some guard against underflow there.
That's a firing rate of about 5/12K lines of code, but I wonder if I were to
send patches for these 3 files that silence the warning I wonder how many would
be approved.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D71607/new/
https://reviews.llvm.org/D71607
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