[PATCH] D105169: [Clang/Test]: Rename enable_noundef_analysis to disable-noundef-analysis and turn it off by default

Florian Hahn via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Thu Jan 20 02:17:42 PST 2022

fhahn added inline comments.

Comment at: clang/lib/CodeGen/CGCall.cpp:2535
         ArgAttrs[FirstIRArg + i] =
             llvm::AttributeSet::get(getLLVMContext(), Attrs);
nlopes wrote:
> fhahn wrote:
> > nlopes wrote:
> > > ab wrote:
> > > > Hmm, if I'm reading this right, this overwrites the `nonnull dereferenceable align` attributes separately computed for `this` around l2335, right? (or `inalloca` and `sret` before that)
> > > > 
> > > > It sounds like an ancient bug, that's only exposed because `noundef` ends up triggering this logic much more often?
> > > > 
> > > > Many of our downstream tests hit this. The hacked up patch seems to do the job; ideally we'd feed the previously-computed attrs when constructing the AttrBuilder (which would also fix the padding argument), but we'd need to match up the IR args first.  Maybe that's fine as a special-case for arg 0 though
> > > nice catch! It's an ancient bug where arg 0 is overwritten.
> > Is anybody looking into a fix or should we revert the patch until this can be properly addressed?
> I would recommend against reverting this patch because of all the followup patches. There were quite a few commits afterwards plus fixes to buildbot configurations, so it's a non-trivial overhead to revert everything.
> I was assuming @ab would fix it as he already root-caused the bug..
FWIW it seems a bit unfortunate that there are some clear regressions when the tests got update, e.g. https://github.com/llvm/llvm-project/commit/1b1c8d83d3567a60280291c0adb95d1d60335509#diff-7e80d593f26f6f6fb24765c6a169884d7350685d565ee970b0a7b9abaf0fb205L355

I'll work with @ab to fix this though rather than reverting, because another revert would cause even more conflicts for us downstream.

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