similar to: MemorySSA question

Displaying 20 results from an estimated 400 matches similar to: "MemorySSA question"

2017 Dec 19
2
MemorySSA question
On Tue, Dec 19, 2017 at 9:10 AM, Siddharth Bhat via llvm-dev < llvm-dev at lists.llvm.org> wrote: > I could be entirely wrong, but from my understanding of memorySSA, each > def defines an "abstract heap state" which has the coarsest possible > definition - any write will be modelled as a "new heap state". > This is true for def-def relationships, but
2017 Feb 17
2
[MemorySSA] inserting or removing memory instructions
In particular, if you want to add support, the right way to know what to rename is (off the top of my head) add a flag or something to have renamepass reset all uses it sees (you only have to change the uses, defs are all linked together and thus already fixed by the updater). Right now it only does that if they have no defining access. Make it skip blocks already in the visited set (the
2018 Aug 09
2
llvm MemorySSA def-use chains
Hi, I have a question about how llvm MemorySSA works, as seems I misunderstand something. Consider following code snippet and corresponding IR with MemorySSA annotations (got with opt -print-memoryssa) void foo(int* b) { int a = 0; int d = 12; if (b) { a = 42; d = 32; } int c = a; int e = d; } ; Function Attrs: noinline nounwind optnone uwtable
2018 Aug 10
2
llvm MemorySSA def-use chains
Hi, try adding some alias analysis to the pipeline: see examples in llvm/test/Analysis/MemorySSA/*.ll for example assume.ll has ; RUN: opt -aa-pipeline=basic-aa -passes='print<memoryssa>,verify<memoryssa>' without basic-aa the memory ssa will safely assume that the stores to %a and %d alias which may be proven disjoint by one of the alias analyses. On Thu, Aug 9, 2018 at 8:37
2017 Feb 17
2
[MemorySSA] inserting or removing memory instructions
Hi guys, a question about updating memory SSA: Is it expected that e.g insertion of MemoryDef doesn't change all dominated uses? For example test case CreateLoadsAndStoreUpdater produces: define void @F(i8*) { ; 1 = MemoryDef(liveOnEntry) store i8 16, i8* %0 ; 4 = MemoryDef(1) store i8 16, i8* %0 br i1 true, label %2, label %3 ; <label>:2: ;
2015 Apr 28
2
[LLVMdev] alias set collapse and LICM
On Mon, Apr 27, 2015 at 4:21 PM, Daniel Berlin <dberlin at dberlin.org> wrote: > You can't win here (believe me, i've tried, and better people than me have > tried, for years :P). > No matter what you do, the partitioning will never be 100% precise. The > only way to solve that in general is to pairwise query over the > partitioning. > > Your basic problem is
2018 Feb 09
1
PHI nodes for atomic variables
Dear Daniel Berlin, I just tried MemorySSA analysis and get the next IR. However, I feel confused by the result. Specifically, why instruction *%3* relates to a *MemoryDef*. According to my understanding, I think *%3* should be related to a *MemoryUse*, right? ; Function Attrs: uwtable define void @_Z2f1v() #3 personality i32 (...)* @__gxx_personality_v0 { entry: ; 1 = MemoryDef(liveOnEntry)
2018 Feb 08
0
PHI nodes for atomic variables
Let me try to help. On Thu, Feb 8, 2018 at 12:13 PM, Qiuping Yi via llvm-dev < llvm-dev at lists.llvm.org> wrote: > Thanks for your explanation. > > Do you mean that LLVM will not maintain the def-use chain for atomic > variables? > It is not a variable at the LLVM level. At the source level, it is a variable. At the LLVM IR level, it is lowered into memory operations. All
2018 Feb 08
3
PHI nodes for atomic variables
Thanks for your explanation. Do you mean that LLVM will not maintain the def-use chain for atomic variables? So it is impossible to directly catch the fact that the load of x at the statement 'data1 = x; ' dependents on data4 (because of the statement x=data4 )? If I want to get such information, may be the only solution is to traverse all the predecessors of the statement 'data1 =
2016 Apr 29
2
[MemorySSA] Potential CachingMemorySSAWalker bug
Hi guys, I think I have run into another CachingMemorySSAWalker cache bug. It's a bit tricky to reproduce, so I'd like to start by trying to show you what is happening when running EarlyCSE with my local changes to use MemorySSA. I've attached a debug log that shows that the value returned by getClobberingMemoryAccess(Inst) after a call to removeMemoryAccess is wrong. The
2016 Jun 27
2
[MemorySSA] Potential bug in MemoryUse defining access calculation
Hey All, I've come across what I believe to be a bug in MemorySSA. George, I wasn't sure if this was a known issue that you'll be addressing in your upcoming walker caching changes or not, so I haven't investigated it very much. The test case is attached. The bug is that the defining access for the second load is set to the loop MemoryPhi node instead of being liveOnEntry as
2016 May 02
2
[MemorySSA] Potential CachingMemorySSAWalker bug
I suspect something is pulling the RHS of the memorydef and caching it for calls it should not be used for. In particular, i suspect we are about to discover we can't cache the results from both versions of getClobberingMemoryAccess together, or that the cache is not always getting consistently written. On Mon, May 2, 2016 at 11:16 AM, George Burgess IV < george.burgess.iv at
2016 May 02
2
[MemorySSA] Potential CachingMemorySSAWalker bug
I've put my changes to EarlyCSE that trigger this case up on phab here: http://reviews.llvm.org/D19821. These changes depend on http://reviews.llvm.org/D19664 so that will need to be applied first. With these changes applied, the original attached .ll file should trigger this bug when compiled with opt -early-cse -early-cse-use-memoryssa On 5/2/2016 2:34 PM, Daniel Berlin wrote: >
2018 Sep 18
1
Generalizing load/store promotion in LICM
On Fri, Sep 14, 2018 at 4:25 PM Philip Reames <listmail at philipreames.com> wrote: > This is going OT from the original thread, but, what the heck... > Sorry, not my intention, I was just giving another reason why getting promotion done in LICM differently would be helpful. > Alina, can you explain the challenge with implementing promotion over > MemorySSA? On the surface, it
2017 Dec 21
4
Hoisting in the presence of volatile loads.
On 12/20/2017 03:49 PM, Alina Sbirlea via llvm-dev wrote: > +Philip to get his input too. > I've talked with George offline, and here's a summary: > > In D16875 <https://reviews.llvm.org/D16875>, the decision made was: > "The LLVM spec is ambiguous about whether we can hoist a non-volatile > load above a volatile load when the loads alias. It's probably
2017 Sep 23
2
Potential infinite loop in MemorySSAUpdater
With regards Bhargav Reddy Godala Software Engineer 2 Bangalore, India E-mail: Bhargav-reddy.Godala at amd.com<mailto:Bhargav-reddy.Godala at amd.com> Ext 30678 On 23-Sep-2017, at 9:27 PM, Daniel Berlin <dberlin at dberlin.org<mailto:dberlin at dberlin.org>> wrote: On Sat, Sep 23, 2017 at 8:38 AM, Godala, Bhargav-reddy via llvm-dev <llvm-dev at
2016 Jun 27
0
[MemorySSA] Potential bug in MemoryUse defining access calculation
This is definitely a caching bug related to this code: 1038 // Don't try to optimize this phi again if we've already tried to do so. 1039 if (!Q.Visited.insert(PHIPair).second) { 1040 ModifyingAccess = CurrAccess; 1041 break; 1042 } We don't differentiate elsewhere between having stopped at a phi because we were path walking and discovered that path
2017 Sep 25
2
Potential infinite loop in MemorySSAUpdater
I understand that changing the starting element to “InsertedPHIs.being() + StartingPHISize” it will be finite but given that InsrtedPHIs is finite. I have a case where one element(same element is appened to InsertedPHIs) is added to InsertedPHIs every time fixupDefs is invoked. I traced the issue why this was happening. template <class RangeType> MemoryAccess
2017 Dec 20
4
Hoisting in the presence of volatile loads.
On 12/20/2017 1:37 PM, Sanjoy Das wrote:> > Fwiw, I was under the impression that regular loads could *not* be > reordered with volatile loads since we could have e.g.: > > int *normal = &global_variable; > volatile int* ptr = 0; > int k = *ptr; // segfaults, and the signal handler writes to *normal > int value = *normal; > > and that we'd have
2017 Sep 23
0
Potential infinite loop in MemorySSAUpdater
On Sat, Sep 23, 2017 at 9:55 AM, Godala, Bhargav-reddy < Bhargav-reddy.Godala at amd.com> wrote: > > With regards > Bhargav Reddy Godala > Software Engineer 2 > Bangalore, India > E-mail: Bhargav-reddy.Godala at amd.com Ext 30678 > > > > On 23-Sep-2017, at 9:27 PM, Daniel Berlin <dberlin at dberlin.org> wrote: > > > > On Sat, Sep 23, 2017 at