[LLVMdev] Assertion in PHIElimination.cpp

[Philipp Brüschweiler]

Thanks! Patch has been submitted.

Cheers,
Philipp

On Wed, 4 Jul 2012 11:00:10 -0700
Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote:
> 
> On Jul 4, 2012, at 5:35 AM, Philipp Brüschweiler <blei42 at gmail.com>
> wrote:
> 
> > Hi everyone
> > 
> > I'm hitting an assertion in PHIElimination.cpp:375.
> > 
> > "Terminator instructions cannot use virtual registers unless"
> > "they are the first terminator in a block!"
> > 
> > I was looking at the code around that location a bit and have not
> > found a reason why this assertion has to hold, except for a comment:
> >      // In our final twist, we have to decide which instruction
> > kills the // register.  In most cases this is the copy, however,
> > the first // terminator instruction at the end of the block may
> > also use the value. // In this case, we should mark *it* as being
> > the killing block, not the // copy.
> > 
> > Again, no reason is given why only the first terminator is allowed
> > to use the register.
> 
> It seems nobody has needed it before.
> 
> commit 2adfa7e9320e79859beb556367ea607a329866b3
> Author: Chris Lattner <sabre at nondot.org>
> Date:   Tue Jan 3 23:12:21 2006
> 
>     Add support for targets (like Alpha) that have terminator
> instructions which use virtual registers.  We now allow the first
> instruction in a block of terminators to use virtual registers, and
> update phi elimination to correctly update livevar when eliminating
> phi's.  This fixes a problem on a testcase Andrew sent me.
>     
>     
>     git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25083
> 91177308-0d34-0410-b5e6-96231b3b80d8
> 
> I don't think it is hard to fix, you simply need to find the last
> terminator reading SrcReg instead of insisting there can only be one. 
> 
> Patches welcome!
> 
> /jakob
>