[llvm-dev] RFC: LTO should use -disable-llvm-verifier

Reid Kleckner via llvm-dev llvm-dev at lists.llvm.org
Mon Aug 31 10:42:08 PDT 2015

On Mon, Aug 31, 2015 at 10:12 AM, Rafael EspĂ­ndola <llvm-dev at lists.llvm.org>

> > Not sure I follow? Generally LTO inputs are going to be "user provided"
> (in the sense that they're not produced immediately prior by the same
> process - or you'd have just produced a single Module in the first place, I
> would imagine) so changing the default still seems problematic in the sense
> of allowing 'unbounded' input without verification...
> The common case is for the bitcode to be generated by a paired clang. Even
> when it is an old bitcode compiled module, the Module itself is created by
> the bitcode reader.
Sure, but it is not uncommon to LTO with old bitcode. We all know it's
pretty easy to crash LLVM with bad bitcode or bad IR. These interfaces are
not thoroughly tested.

I think verifying the result of the bitcode reader by default during LTO is
probably the right thing for the foreseeable future. It's the only thing
that has any hope of telling the user something useful when things go wrong.

I'd like it if we spent a little effort understanding why it's slow before
flipping it off. Maybe the verifier is running multiple times, instead of
after deserialization. We shouldn't need that in release builds.
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