[llvm] r334118 - [Debugify] Move debug value intrinsics closer to their operand defs

[Davide Italiano via llvm-commits]

On Wed, Jun 6, 2018 at 12:05 PM, Vedant Kumar via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
> Author: vedantk
> Date: Wed Jun  6 12:05:42 2018
> New Revision: 334118
>
> URL: http://llvm.org/viewvc/llvm-project?rev=334118&view=rev
> Log:
> [Debugify] Move debug value intrinsics closer to their operand defs
>
> Before this patch, debugify would insert debug value intrinsics before the
> terminating instruction in a block. This had the advantage of being simple,
> but was a bit too simple/unrealistic.
>
> This patch teaches debugify to insert debug values immediately after their
> operand defs. This enables better testing of the compiler.
>
> For example, with this patch, `opt -debugify-each` is able to identify a
> vectorizer DI-invariance bug fixed in llvm.org/PR32761. In this bug, the
> vectorizer produced different output with/without debug info present.
>
> Reverting Davide's bugfix locally, I see:
>

Another idea that came to my mind and I wanted to discuss
with you in person yesterday (although we didn't get a chance) is that
we could randomize the insertion of the debug value intrinsic (using
`OrderedBasicBlock`or the dominator directly to make sure the
dominance relation is enforced).
I'm not entirely sure if it's going to find new bugs, but maybe it's
worth a shot.

--
Davide