search for: underdefin

...t need it in a public > header. Out of curiosity, what are you looking to use the latice values > for? Why not just run SCCP and then look at the transformed code? I was planning to write an analysis pass that checks the expression at every conditional statement to see whether the value is underdefined or not. This would be after SCCP and other optimizations have already been run, so conditional statements with constant expressions would already be eliminated. (Am I being silly? There isn't a pass to eliminate conditionals on underdefined variables is there?) It would be fine for my purpos...

...>> header. Out of curiosity, what are you looking to use the latice values >> for? Why not just run SCCP and then look at the transformed code? > > I was planning to write an analysis pass that checks the expression at > every conditional statement to see whether the value is underdefined or > not. Then just run the SCCP pass, and check to see if any operands satisfy the predicate "isa<UndefValue>(V)". LLVM explicitly represents undefined values. > This would be after SCCP and other optimizations have already been > run, so conditional statements with...

...Out of curiosity, what are you looking to use the latice values >>> for? Why not just run SCCP and then look at the transformed code? >> >> I was planning to write an analysis pass that checks the expression at >> every conditional statement to see whether the value is underdefined or >> not. > > Then just run the SCCP pass, and check to see if any operands satisfy > the predicate "isa<UndefValue>(V)". LLVM explicitly represents > undefined values. I have a case where it doesn't, but perhaps the SCCP pass isn't to blame: exter...

On Tue, 9 May 2006, Nick Lewycky wrote: >>> For an analysis pass, I'm interested in reading the lattice values >>> calculated by SCCP. Should I split the current SCCP optimization into an >>> analysis piece and the optimization that depends on it, so that I can >>> use its analysis results? >> >> SCCP is already split into an SCCPSolver class

Chris Lattner wrote: > On Tue, 9 May 2006, Nick Lewycky wrote: > >> For an analysis pass, I'm interested in reading the lattice values >> calculated by SCCP. Should I split the current SCCP optimization into an >> analysis piece and the optimization that depends on it, so that I can >> use its analysis results? > > SCCP is already split into an SCCPSolver

----- Original Message ----- > From: "Daniel Berlin via llvm-dev" <llvm-dev at lists.llvm.org> > To: "Joerg Sonnenberger" <joerg at britannica.bec.de>, "llvm-dev" > <llvm-dev at lists.llvm.org> > Sent: Thursday, January 14, 2016 10:38:10 AM > Subject: Re: [llvm-dev] High memory use and LVI/Correlated Value > Propagation > On

...into an undef value. If you wanted to tackle this, it should be straight-forward and would be a worthwhile addition to the LLVM optimizer. > I thought this might be because the optimizer is being conservative > about correctness, but that the lattice must still show it as > underdefined -- but obviously as I haven't looked at the lattice > directly, I haven't verified that yet. Yup, if there is a load from a memory location on the stack, SCCP won't touch it: it will assume it is overdefined. > Maybe it becomes overdefined as the constant can't be resolv...

...ion. Someone should be doing a check with indexValid to see if instead it should be marking as undefined. I can try to produce such a patch. >> I thought this might be because the optimizer is being conservative >> about correctness, but that the lattice must still show it as >> underdefined -- but obviously as I haven't looked at the lattice >> directly, I haven't verified that yet. > > > Yup, if there is a load from a memory location on the stack, SCCP won't > touch it: it will assume it is overdefined. > >> Maybe it becomes overdefined as...