[LLVMdev] weird issue with mem2reg, should have guessed

[Patrick Meredith]

----- Original Message ----- 
From: "Chris Lattner" <sabre at nondot.org>
To: <llvmdev at cs.uiuc.edu>
Sent: Wednesday, June 23, 2004 4:24 PM
Subject: Re: [LLVMdev] weird issue with mem2reg, should have guessed


> On Wed, 23 Jun 2004, Patrick Meredith wrote:
>
> > What's different about code that's been mem2reg'd from straight front
end
> > code, or anything that mem2reg hasn't been run on?  PHINODES!
>
> Yup, front-ends generally don't produce SSA form. :)
>
> > It appears to be crashing when I try to cast a Value* that's really a
> > BB* (from the PHInode operands) to a User*, insteresting since I am
> > dyn_casting.  I just caught this on cerr though (printing out what the
> > Value* was each time).
>
> Yeah, you shouldn't do that. :)  Also, you should use the 'cast' template
> instead of the dyn_cast template unless you are prepared to handle the
> null return value.  Use 'cast' when you _know_ that something is a
> particular type.  This will give you a nice assertion failure instead of a
> segfault when you deref the null pointer :)

I am handling null, I'm using the if( something* s =
dyn_cast<something>(something_else){ } construct.  It's the fact that I was
using getOperand(1) on a call instruction that should always have an
operand.... (the 0th operand is the function, the 1st should be the
paramter).  For some reason this error only pops up after mem2reg.  But I
need to change this so that I am not adding whole basic blocks to my program
value set anyway.



> > Let me check bugpoint.
>
> Cool, post the testcase it produces.  Hopefully it will be small :)
>
> -Chris
>
> > ----- Original Message -----
> > From: "Misha Brukman" <brukman at uiuc.edu>
> > To: <llvmdev at cs.uiuc.edu>
> > Sent: Wednesday, June 23, 2004 3:56 PM
> > Subject: Re: [LLVMdev] weird issue with mem2reg
> >
> >
> > > On Wed, Jun 23, 2004 at 03:50:09PM -0500, Patrick Meredith wrote:
> > > > MetaSplit is an anlysis I just finished writing.  It doesn't alter
> > > > anything, all it does is build a set of "program instructions".  For
> > > > some reason even though if I run it with any other combination of
> > > > passes I've found, anytime I run it with mem2reg I get a seg fault
in
> > > > dyn_cast!  Here's output:
> > >
> > > Since the crash is after your code is entered, the problem is probably
> > > not in mem2reg, but in your pass.  To see if that's the case, you can
do
> > > this:
> > >
> > > % opt -mem2reg < orig.bc > m2r.bc
> > > % opt -load=... -metasplit < m2r.bc > output.bc
> > >
> > > And see if it crashes in mem2reg or in your pass.  To narrow your
> > > testcase down further, we recommend the use of bugpoint, the automatic
> > > test case reducer:
> > >
> > >   http://llvm.cs.uiuc.edu/docs/HowToSubmitABug.html
> > >
> > > In this case, this should work:
> > >
> > > % bugpoint -load=... -mem2reg -metasplit orig.bc
> > >
> > > --
> > > Misha Brukman :: http://misha.brukman.net :: http://llvm.cs.uiuc.edu
> > >
> > > _______________________________________________
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> >
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> >
>
> -Chris
>
> -- 
> http://llvm.cs.uiuc.edu/
> http://www.nondot.org/~sabre/Projects/
>
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