ahatanak added a subscriber: aeubanks.
ahatanak added inline comments.
================
Comment at: clang/lib/CodeGen/Address.h:67
return;
- // Currently the max supported alignment is much less than 1 << 63 and is
+ // Currently the max supported alignment is much less than 1 << 32 and is
// guaranteed to be a power of 2, so we can store the log of the alignment
----------------
efriedma wrote:
> ahatanak wrote:
> > efriedma wrote:
> > > ahatanak wrote:
> > > > efriedma wrote:
> > > > > This comment isn't right. The max alignment is, as far as I can
> > > > > tell, 1<<32 exactly. (But there's something weird going on with very
> > > > > large values... somehow `int a[1LL<<32]
> > > > > __attribute((aligned(1ULL<<32))) = {};` ignores the alignment.)
> > > > The following function generated by tablegen (and a few others directly
> > > > or indirectly calling the function) returns a 32-bit int, but it should
> > > > be returning a 64-bit int.
> > > >
> > > > https://github.com/llvm/llvm-project/blob/main/clang/utils/TableGen/ClangAttrEmitter.cpp#L532
> > > Filed https://github.com/llvm/llvm-project/issues/60752 so we don't lose
> > > track of this.
> > I just realized we can't reduce the number of bits used for alignment here
> > as we need 6 bits for alignment of `1 << 32`.
> >
> > Should we allocate additional memory when `AlignLog` is either 31 or 32? If
> > the 5-bit alignment is equal to `0b11111`, it would mean that there is an
> > out-of-line storage large enough to hold the alignment and any other extra
> > information that is needed. I think
> > https://reviews.llvm.org/D117262#3267899 proposes a similar idea.
> How much does `sizeof(Address)` actually matter, anyway? If it's going to
> get that nasty to implement the packing, I'm not sure it's worth the effort
> to optimize.
I'm not sure, but apparently https://reviews.llvm.org/D117262 was needed to
reduce the memory usage.
I don't see a significant increase in stack usage (a little over 1%) in the
files in `clang/lib/CodeGen` when I build clang with `-fstack-usage`.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D142584/new/
https://reviews.llvm.org/D142584
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