[LLVMdev] choice between SSAPRE and bitvector aporach
isanbard at gmail.com
Fri Apr 4 17:29:20 PDT 2008
On Fri, Apr 4, 2008 at 2:58 PM, Vikram S. Adve <vadve at cs.uiuc.edu> wrote:
> On Apr 4, 2008, at 4:51 PM, Daniel Berlin wrote:
> > On Fri, Apr 4, 2008 at 2:38 AM, Bill Wendling <isanbard at gmail.com>
> > wrote:
> >> On Apr 2, 2008, at 10:11 PM, Xuehai Qian wrote:
> >>> Hi LLVMers,
> >>> I am a PHD student in CS dept in UIUC, I am doing a project for
> >>> Vikram's course, it is about PRE. I would like to know why you
> >>> didn't
> >>> choose SSAPRE in LLVM, since it seems to be more suitable for LLVM
> >>> (it
> >>> can operate directly on SSA form and avoid the conversion between
> >>> SSA
> >>> and bit-vector). Can anyone tell me the reason?
> >> Hi Xuehai,
> >> If I remember correctly, there were several details that the paper
> >> assumed that made adapting it to work in LLVM very difficult.
> > It would at least require side-data structures to store the
> > occurrences and expression phis.
> Doesn't the paper also assume the invariant that phi operands are
> effectively dead after the Phi, which is true right after SSA is
> constructed, but potentially not after transformations?
Yes, I think that that was the major problem with it.
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