[llvm-dev] GVN / Alias Analysis issue with llvm.masked.scatter/gather intrinsics

Hal Finkel via llvm-dev llvm-dev at lists.llvm.org
Tue Aug 30 13:11:57 PDT 2016 

----- Original Message -----

> From: "Daniel Berlin" <dberlin at dberlin.org>
> To: "Philip Reames" <listmail at philipreames.com>, "Davide Italiano"
> <davide at freebsd.org>, "Chandler Carruth" <chandlerc at gmail.com>
> Cc: "Chris Sakalis" <chrissakalis at gmail.com>, "David Majnemer"
> <david.majnemer at gmail.com>, "Hal Finkel" <hfinkel at anl.gov>,
> "llvm-dev" <llvm-dev at lists.llvm.org>
> Sent: Tuesday, August 30, 2016 3:07:01 PM
> Subject: Re: [llvm-dev] GVN / Alias Analysis issue with
> llvm.masked.scatter/gather intrinsics

> This is now committed and a test added to GVN.

Thanks! 

I suspect that, in practice, we'll get little benefit from handling this until our AA passes learn how to deal with (i.e. look back through) pointer vectors. 

-Hal 

> On Mon, Aug 29, 2016 at 1:59 PM, Daniel Berlin < dberlin at dberlin.org
> > wrote:

> > Okay, so then it sounds like, for now, the right fix is to stop
> > marking masked.gather and masked.scatter with intrarg* options.
> 

> > On Mon, Aug 29, 2016, 1:26 PM Philip Reames <
> > listmail at philipreames.com > wrote:
> 

> > > We might have specification bug here, but we appear to implement
> > > what
> > > we specified. argmemonly is specified as only considering pointer
> > > typed arguments. It's behavior on vector-of-pointers is
> > > unspecified,
> > > but would seem to fall into the same case as inttoptr of an
> > > integer
> > > argument (i.e. explicitly undefined). We could consider changing
> > > that.
> > 
> 

> > > On 08/29/2016 11:59 AM, Daniel Berlin wrote:
> > 
> 

> > > > + a few others.
> > > 
> > 
> 

> > > > After following this rabbit hole a bit, there are a lot of
> > > > mutually
> > > > recursive calls, etc, that may or may not do the right thing
> > > > with
> > > > vectors of pointers.
> > > 
> > 
> 
> > > > I can fix *this* particular bug with the attached patch.
> > > 
> > 
> 

> > > > However, it's mostly papering over stuff. Nothing seems to know
> > > > what
> > > > to do with a memorylocation that is a vector of pointers. They
> > > > all
> > > > expect memorylocation to be a single pointer location.
> > > 
> > 
> 

> > > > I would chalk it up to "luck" that this patch fixes the bug.
> > > 
> > 
> 

> > > > It's pretty clear that MemoryLocation doesn't fit the needs of
> > > > a
> > > > lot
> > > > of stuff anymore (we hacked AA nodes into it, and lots of stuff
> > > > now
> > > > tries to figure out the invariantess of the locations, blah
> > > > blah
> > > > blah), but it seems like a big job to figure out what to
> > > > replace
> > > > it
> > > > with that will work for these cases.
> > > 
> > 
> 

> > > > (I'm pretty positive if we just make it MemoryLocations, and
> > > > have
> > > > everything loop over the locations, the compiler will get a lot
> > > > larger and a lot slower)
> > > 
> > 
> 

> > > > On Mon, Aug 29, 2016 at 9:10 AM, Daniel Berlin <
> > > > dberlin at dberlin.org
> > > > > wrote:
> > > 
> > 
> 

> > > > > it would also, for that matter, say the same about an array
> > > > > of
> > > > > pointers.
> > > > 
> > > 
> > 
> 

> > > > > It's not clear to me what will break if you change this to
> > > > > isPtrOrPtrVectorTy.
> > > > 
> > > 
> > 
> 

> > > > > In fact, i know it doesn't fix this bug.
> > > > 
> > > 
> > 
> 
> > > > > It's a pretty deep rabbit hole of things not quite prepared
> > > > > to
> > > > > understand vectors of pointers.
> > > > 
> > > 
> > 
> 

> > > > > (we prepare memorylocations of them, but memory locations
> > > > > expect
> > > > > to
> > > > > be one thing, not a group of things, etc).
> > > > 
> > > 
> > 
> 

> > > > > On Mon, Aug 29, 2016 at 8:58 AM, Daniel Berlin <
> > > > > dberlin at dberlin.org
> > > > > > wrote:
> > > > 
> > > 
> > 
> 

> > > > > > this is definitely a bug in AA.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > 225 for (auto I = CS2.arg_begin(), E = CS2.arg_end(); I !=
> > > > > > E;
> > > > > > ++I)
> > > > > > {
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > 226 const Value *Arg = *I;
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > 227 if (!Arg->getType()->isPointerTy())
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > -> 228 continue;
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > 229 unsigned CS2ArgIdx = std::distance(CS2.arg_begin(), I);
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > 230 auto CS2ArgLoc = MemoryLocation::getForArgument(CS2,
> > > > > > CS2ArgIdx,
> > > > > > TLI);
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > AliasAnalysis.cpp:228
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > It ignores every argument because they are vectors of
> > > > > > pointers,
> > > > > > not
> > > > > > pointers.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > I'm surprised this has not broken anything before. It will
> > > > > > never
> > > > > > say
> > > > > > two intrinsics with vectors of pointers mod/ref each other.
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > On Mon, Aug 29, 2016 at 7:36 AM, Davide Italiano <
> > > > > > davide at freebsd.org
> > > > > > > wrote:
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > + Daniel Berlin
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > On Mon, Aug 29, 2016 at 3:42 PM, Chris Sakalis via
> > > > > > > llvm-dev
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > < llvm-dev at lists.llvm.org > wrote:
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > Hello everyone,
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > I think I have found an gvn / alias analysis related
> > > > > > > > bug,
> > > > > > > > but
> > > > > > > > before opening
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > an issue on the tracker I wanted to see if I am missing
> > > > > > > > something.
> > > > > > > > I have
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > the following testcase:
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> define spir_kernel void @test(<2 x i32*> %in1, <2 x
> > > > > > > >> i32*>
> > > > > > > >> %in2,
> > > > > > > >> i32* %out)
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> {
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> entry:
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; Just some temporary storage
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.0 = alloca i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.1 = alloca i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.i = insertelement <2 x i32*> undef, i32* %tmp.0,
> > > > > > > >> i32
> > > > > > > >> 0
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp = insertelement <2 x i32*> %tmp.i, i32* %tmp.1,
> > > > > > > >> i32
> > > > > > > >> 1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; Read from in1 and in2
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %in1.v = call <2 x i32> @llvm.masked.gather.v2i32(<2 x
> > > > > > > >> i32*>
> > > > > > > >> %in1,
> > > > > > > >> i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> 1, <2 x i1> <i1 true, i1 true>, <2 x i32> undef) #1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %in2.v = call <2 x i32> @llvm.masked.gather.v2i32(<2 x
> > > > > > > >> i32*>
> > > > > > > >> %in2,
> > > > > > > >> i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> 1, <2 x i1> <i1 true, i1 true>, <2 x i32> undef) #1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; Store in1 to the allocas
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> call void @llvm.masked.scatter.v2i32(<2 x i32> %in1.v,
> > > > > > > >> <2
> > > > > > > >> x
> > > > > > > >> i32*>
> > > > > > > >> %tmp,
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> i32 1, <2 x i1> <i1 true, i1 true>);
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; Read in1 from the allocas
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.v.0 = call <2 x i32> @llvm.masked.gather.v2i32(<2
> > > > > > > >> x
> > > > > > > >> i32*>
> > > > > > > >> %tmp, i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> 1, <2 x i1> <i1 true, i1 true>, <2 x i32> undef) #1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; Store in2 to the allocas
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> call void @llvm.masked.scatter.v2i32(<2 x i32> %in2.v,
> > > > > > > >> <2
> > > > > > > >> x
> > > > > > > >> i32*>
> > > > > > > >> %tmp,
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> i32 1, <2 x i1> <i1 true, i1 true>);
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; Read in2 from the allocas
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.v.1 = call <2 x i32> @llvm.masked.gather.v2i32(<2
> > > > > > > >> x
> > > > > > > >> i32*>
> > > > > > > >> %tmp, i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> 1, <2 x i1> <i1 true, i1 true>, <2 x i32> undef) #1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; Store in2 to out for good measure
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.v.1.0 = extractelement <2 x i32> %tmp.v.1, i32 0
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.v.1.1 = extractelement <2 x i32> %tmp.v.1, i32 1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> store i32 %tmp.v.1.0, i32* %out
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %out.1 = getelementptr i32, i32* %out, i32 1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> store i32 %tmp.v.1.1, i32* %out.1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ret void
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> }
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > It uses a masked scatter operation to store a value to
> > > > > > > > the
> > > > > > > > two
> > > > > > > > allocas and
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > then uses a masked gather operation to read that same
> > > > > > > > value.
> > > > > > > > This
> > > > > > > > is done
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > twice in a row, with two different values. If I run
> > > > > > > > this
> > > > > > > > code
> > > > > > > > through the
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > GVN pass, the second gather (%tmp.v.1) will be deemed
> > > > > > > > to
> > > > > > > > be
> > > > > > > > the
> > > > > > > > same as the
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > first gather (%tmp.v.0) and it will be removed. After
> > > > > > > > some
> > > > > > > > debugging, I
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > realized that this is happening because the Memory
> > > > > > > > Dependence
> > > > > > > > Analysis
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > returns %tmp.v.0 as the Def dependency for %tmp.v.1,
> > > > > > > > even
> > > > > > > > though
> > > > > > > > the scatter
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > call in between changes the value stored at %tmp. This,
> > > > > > > > in
> > > > > > > > turn,
> > > > > > > > is
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > happening because the alias analysis is returning
> > > > > > > > NoModRef
> > > > > > > > for
> > > > > > > > the
> > > > > > > > %tmp.v.1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > and second scatter callsites. The resulting IR produces
> > > > > > > > the
> > > > > > > > wrong
> > > > > > > > result:
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> define spir_kernel void @test(<2 x i32*> %in1, <2 x
> > > > > > > >> i32*>
> > > > > > > >> %in2,
> > > > > > > >> i32* %out)
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> {
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> entry:
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.0 = alloca i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.1 = alloca i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.i = insertelement <2 x i32*> undef, i32* %tmp.0,
> > > > > > > >> i32
> > > > > > > >> 0
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp = insertelement <2 x i32*> %tmp.i, i32* %tmp.1,
> > > > > > > >> i32
> > > > > > > >> 1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %in1.v = call <2 x i32> @llvm.masked.gather.v2i32(<2 x
> > > > > > > >> i32*>
> > > > > > > >> %in1,
> > > > > > > >> i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> 1, <2 x i1> <i1 true, i1 true>, <2 x i32> undef) #1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %in2.v = call <2 x i32> @llvm.masked.gather.v2i32(<2 x
> > > > > > > >> i32*>
> > > > > > > >> %in2,
> > > > > > > >> i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> 1, <2 x i1> <i1 true, i1 true>, <2 x i32> undef) #1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> call void @llvm.masked.scatter.v2i32(<2 x i32> %in1.v,
> > > > > > > >> <2
> > > > > > > >> x
> > > > > > > >> i32*>
> > > > > > > >> %tmp,
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> i32 1, <2 x i1> <i1 true, i1 true>)
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.v.0 = call <2 x i32> @llvm.masked.gather.v2i32(<2
> > > > > > > >> x
> > > > > > > >> i32*>
> > > > > > > >> %tmp, i32
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> 1, <2 x i1> <i1 true, i1 true>, <2 x i32> undef) #1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> call void @llvm.masked.scatter.v2i32(<2 x i32> %in2.v,
> > > > > > > >> <2
> > > > > > > >> x
> > > > > > > >> i32*>
> > > > > > > >> %tmp,
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> i32 1, <2 x i1> <i1 true, i1 true>)
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ; The call to masked.gather is gone and now we are
> > > > > > > >> using
> > > > > > > >> the
> > > > > > > >> old
> > > > > > > >> value
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> (%tmp.v.0)
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.v.1.0 = extractelement <2 x i32> %tmp.v.0, i32 0
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %tmp.v.1.1 = extractelement <2 x i32> %tmp.v.0, i32 1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> store i32 %tmp.v.1.0, i32* %out
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> %out.1 = getelementptr i32, i32* %out, i32 1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> store i32 %tmp.v.1.1, i32* %out.1
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> ret void
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >> }
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > The old value read from %tmp is used, instead of the
> > > > > > > > new
> > > > > > > > one.
> > > > > > > > I
> > > > > > > > tested this
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > code using `opt -gvn`, with LLVM 3.8.1. I also tried
> > > > > > > > tip
> > > > > > > > (84cb7f4)
> > > > > > > > with the
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > same result.
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > I should mention that if I replace the second scatter
> > > > > > > > with
> > > > > > > > stores,
> > > > > > > > the issue
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > persists. The only way to avoid it is to replace all
> > > > > > > > scatter/gather
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > intrinsics with equivalent sets of store/load, in which
> > > > > > > > case
> > > > > > > > the
> > > > > > > > MemDep
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > returns the correct dependencies and the GVN pass will
> > > > > > > > not
> > > > > > > > remove
> > > > > > > > the second
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > set of loads.
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > So, my question is, is this a bug or am I doing
> > > > > > > > something
> > > > > > > > that
> > > > > > > > I
> > > > > > > > shouldn't
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > be in the IR? And if it is a bug, is it the AA analyses
> > > > > > > > that
> > > > > > > > return
> > > > > > > > the
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > wrong result (I presume so) or should GVN handle such
> > > > > > > > cases
> > > > > > > > differently?
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > Best regards,
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > Chris
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > _______________________________________________
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > LLVM Developers mailing list
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > llvm-dev at lists.llvm.org
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > >
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > --
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > Davide
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > > > "There are no solved problems; there are only problems
> > > > > > > that
> > > > > > > are
> > > > > > > more
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > > or less solved" -- Henri Poincare
> > > > > > 
> > > > > 
> > > > 
> > > 
> > 
> 

-- 

Hal Finkel 
Assistant Computational Scientist 
Leadership Computing Facility 
Argonne National Laboratory 
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