efriedma added inline comments.
================
Comment at: lib/Basic/TargetInfo.cpp:229
switch (BitWidth) {
- case 96:
+ case 80:
if (&getLongDoubleFormat() == &llvm::APFloat::x87DoubleExtended)
----------------
ddcc wrote:
> bruno wrote:
> > The change makes sense but I believe there's some historical reason why
> > this is 96 instead of 80? What problem have you found in practice? Do you
> > have a testcase or unittest that exercise the issue (and that could be
> > added to the patch)?
> I'd be curious why it was historically set to 96; I dug up rL190044 as the
> original commit, but it doesn't mention 80 vs 96 for this at all.
>
> I've been implementing an alternative symbolic constraint solver backend for
> the static analyzer, including floating-point support, which performs some
> type conversion and needs to reason about bitwidth. I'm still working on
> those patches, since they touch a lot of code and currently break some tests.
> I can write up a testcase for this issue, though I've only written IR
> testcases before and I'm not sure how I'd directly call a clang internal
> function?
It was set to 96 because that's what the only caller (handleModeAttr) expects;
see https://reviews.llvm.org/rL65935 and https://reviews.llvm.org/rL190926.
It's arbitrary as far as I know.
https://reviews.llvm.org/D26955
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