[llvm-dev] Hash of a module
Philip Reames via llvm-dev
llvm-dev at lists.llvm.org
Tue Dec 22 10:45:57 PST 2015
On 12/21/2015 09:29 AM, Robinson, Paul via llvm-dev wrote:
> | (canonicalizeOperands swaps arguments of an and and then
> ReassociateExpression swaps them back).
> That feels like its own bug, canonicalize and reassociate having
> different opinions of canonical order. Just saying.
It definitely is. However, we seem to have a good number of these types
of bugs. Nothing in our current test infrastructure reveals them, so
they seem to be relatively widespread.
Might be worthing adding an assertion to the pass manager that the hash
of a changed module differs from the hash of the original?
> *From:*llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
> *Artur Pilipenko via llvm-dev
> *Sent:* Monday, December 21, 2015 9:11 AM
> *To:* Russell Wallace
> *Cc:* llvm-dev
> *Subject:* Re: [llvm-dev] Hash of a module
> There is a caveat here. I was experimenting with something similar and
> found that this status is not always trustworthy. I fixed one bug in
> prune-eh. These is also a bug in reassociate pass. It returns true
> with no change made on the following instruction:
> %0 = and i64 %b, %a
> It happens because it performs two distinct transformations which
> nullify each other (canonicalizeOperands swaps arguments of an and and
> then ReassociateExpression swaps them back).
> This approach might work for your set of passes, but beware of the
> On 21 Dec 2015, at 19:59, Russell Wallace
> <russell.wallace at gmail.com <mailto:russell.wallace at gmail.com>> wrote:
> Yes, I'm running all the existing passes that I know how to run. I
> didn't know they returned change-made. Thanks!
> On Mon, Dec 21, 2015 at 12:36 PM, Artur Pilipenko
> <apilipenko at azulsystems.com <mailto:apilipenko at azulsystems.com>>
> Are you going to run some of the existing passes? Why can’t you
> just use the returned change-made value from the passes?
> > On 20 Dec 2015, at 15:43, Russell Wallace via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
> > I want to run a bunch of optimizations, iteratively, that is
> keep running until things stop changing (to make sure all
> optimization opportunities are taken). As far as I know, there is
> no way to copy a module or compare modules by value, so it occurs
> to me that a practical solution might be to take the hash code of
> the module and see if that changes.
> > A problem is that hash algorithms are designed to work on
> streams of bytes, not compound objects.
> > First attempt at a solution: iterate through all instructions in
> all functions and hash the instruction kinds. I can think of some
> possible changes that would fail to be captured by that.
> > Is there any already known solution?
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