similar to: Eliminate some two entry PHI nodes - SimplifyCFG

Conditional on the target supporting cmov? Though that's probably not optimal. On Wed, Feb 5, 2020, 7:47 AM Nicolai Hähnle <nhaehnle at gmail.com> wrote: > Hi Ryan, > > On Mon, Feb 3, 2020 at 7:08 PM Ryan Taylor via llvm-dev > <llvm-dev at lists.llvm.org> wrote: > > SimplifyCFG FoldTwoEntryPhiNode looks to simplify all 2 entry phi nodes > in a block, if it

Hey all - me again, So I'm looking at llvm.expect specifically for branch hints. In the following example LLVM will hoist the pow/cos calls into the entry block even though I've used the llvm.expect intrinsic to make it clear that one of the calls is unlikely to occur. target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" target triple =

Hello, in the description of SimplifyCFG, it says that it can "Eliminates PHI nodes for basic blocks with a single predecessor." I tested this pass with a program that has phi nodes with a single predecessor and it did not remove it. I also looked in the code and found nothing to remove it. I'm I missing something, or it does not remove phis with a single predecessor? My

Here's what I've got so far - it seems to work, aside from the fact that DeleteDeadPHIs is not removing at least one dead PHI in my test program. --------------------- static bool mergeBlockIntoSuccessor(BasicBlock *pred, BasicBlock *succ) { if (succ == pred) return false; if (pred->getFirstNonPHI() != pred->getTerminator()) return false; //

On Feb 1, 2011, at 1:34 PM, Andrew Trick wrote: > On Feb 1, 2011, at 1:08 PM, Andrew Clinton wrote: > >> I have a (non-entry) basic block that contains only PHI nodes and an >> unconditional branch (that does not branch to itself). Is it always >> possible to merge this block with it's successor and produce a >> semantically equivalent program? I'm

> On Aug 15, 2018, at 10:57 PM, Hal Finkel via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > > On 08/15/2018 02:38 PM, Philip Reames via llvm-dev wrote: >> I'm concerned that we're focusing on one side of this. Let me point out a few concerns w/changing the canonical form here: >> >> LICM does not know how to hoist or sink regions. It does know

Summary ======= I'm planning on adjusting SimplifyCFG so that it doesn't turn two-entry phi nodes into selects until later in the pass pipeline, to give passes which can understand phis but not selects more opportunity to optimize. The thing I'm trying to do which made me think of doing this is described below, but from the benchmarking I've done it looks like this is overall a

I'm concerned that we're focusing on one side of this.  Let me point out a few concerns w/changing the canonical form here: 1. LICM does not know how to hoist or sink regions.  It does know how to hoist and sink selects. 2. InstCombine has limited support for triangles/diamonds, but fairly extensive support for selects. 3. EarlyCSE and GVN do not know how to eliminate fully

Hello, I’m getting some failures on our internal testing happening after this commit. I dug a little bit into it and it ended up begin caused by the fact that this optimization is sinking some instructions that shouldn’t be sunk In particular we have some loads that need to have a constant address to be selected, because they load from a “special address space”. What the optimization is doing

Probably the issue is solvable in some Codegen prepare pass. That said I still believe some kind of control on if we would like to implement this or not could be useful. Just a question. Why implementing it in SimplifyCFG and not as a separate pass like JumpThreading or something like that? The transformation itself doesn’t seem to fit much in SimplifyCFG. > On 2 Sep 2016, at 13:35, Michael

I guess I thought that once I redirected the branches and created new PHIs that LLVM would correct the variable usage when I return true (changed CFG) from the pass. Is this not the case? On Wed, Mar 7, 2012 at 4:08 PM, Ryan Taylor <ryta1203 at gmail.com> wrote: > Here is the code snippet that I am using to create the PHIs in the loop > according to the PHIs in the new preheader. At

Here is the code snippet that I am using to create the PHIs in the loop according to the PHIs in the new preheader. At this point I have already redirected the loop backedge and removed the preheader from the loop. for (BasicBlock::iterator II = loopHeaderBB->begin(); (PN=dyn_cast<PHINode>(II)); ++II) { // remove loop back PHI and add it to split BB

On 30.8.2011, at 19.19, Eli Friedman wrote: > reg2mem won't do quite this transformation... not sure exactly what you need. I need to get rid of phis. This code is compiled from C++ and for some functions there are no phis, but multiple call instructions. I am targeting hardware in the end, and the next tool reading the IR does not like phis when it's generating VHDL. My questions may

> the next tool reading the IR does not like phis when it's generating VHDL. If you're doing a conversion from LLVM IR to some other non-SSA IR (like the tool's), you can do the phi node removal yourself as you convert. Basically, every predecessor block referenced by a phi node will have an assignment to that variable before branching. There are techniques to make the resultant

Does LLVM have loop multiversioning ? it seems it does not with clang++ -O3 -mllvm -debug-pass=Arguments program.c -c bash-4.1$ clang++ -O3 -mllvm -debug-pass=Arguments fast_algorithms.c -c clang-3.6: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated Pass Arguments: -datalayout -notti -basictti -x86tti -targetlibinfo -no-aa -tbaa -scoped-noalias

Hi Danny, Thanks for that :) However I've just updated the prototype patch to NewGVN and it didn't need any API changes - all I rely on is GVNExpression. Hongbin, I wanted to explain a little about what GVNSink can currently do, what it was designed for and hopefully how to make it handle your testcase. *Background* Common code sinking is more difficult to efficently do than one might

I have attached a case of what I am trying to do, I'm pretty sure I'm just missing some simple API call. In the cfg you can see that although Im setting "lsr.iv441" as "lsr.iv44" from for.body.387.i it's not propagating that through the block or graph. On Wed, Mar 7, 2012 at 12:03 PM, Ryan Taylor <ryta1203 at gmail.com> wrote: > I am splitting a one BB

I am splitting a one BB loop into two BB. Basically, the one loop BB has 3 incoming values, one form back edge two from other edges. I want to extract the PHIs from the other two edges out into it's own BB and delete that from the loop, then redirect the backedge to the loopbody (non extracted portion) and create a new PHI coming from the extracted BB and the backedge. I can do this;

Misha Brukman wrote: > LLVM Machine code is in SSA. This explains quite a lot. I though it's possible to just reduce convert phis into copy instructions in predecessors -- all of which will have the same destination register. > gets you two definitions of r. So we have machine PHI nodes merge the > two possible values into one for result of r. These phis get removed > after

It sounds like Transforms/Utils/SSAUpdater may be what you are looking for. A good example of how to use it -- one that sounds very similar to what you're doing -- can be found in Transforms/Scalar/LoopRotation.cpp On Wed, Mar 7, 2012 at 2:03 PM, Ryan Taylor <ryta1203 at gmail.com> wrote: > I am splitting a one BB loop into two BB. > > Basically, the one loop BB has 3 incoming