[swift-dev] DebugScope Verification Error

[Adrian Prantl]

> On Jan 16, 2018, at 1:20 PM, Vedant Kumar <vsk at apple.com> wrote:
> 
> + Adrian and Davide, since they work in this area.
> 
> Hi Raj,
> 
>> On Jan 15, 2018, at 4:48 PM, Raj Barik via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> 
>> Thanks Mark. You are right, the following assertion fails
>> 
>> require(!DS || DS->getParentFunction() == I->getFunction(),
>>             "debug scope of instruction belongs to a different function");
>> 
>> I am not sure if we need such a check.
> 
> This check exists to ensure that the debug info generated for a program is helpful. For example, a function with the wrong debug scope attached might make for confusing backtraces.

It's more than just confusing backtraces. If these invariants aren't met the LLVM IR generated from this SIL will not pass the LLVM IR verifier or in older versions even crash LLVM.

The constraint being checked in this assertion is that each instruction must be in a lexical scope whose top-level ancestor is the function itself. I.e., it is not legal to move an instruction from one function to another with updating that instruction's debug information by either reparenting it into the new function or by creating inline information for it. SILClonerWithScope implements this re-parenting of instructions into a new function for you.

-- adrian

> 
> vedant
> 
>>   
>> 
>> On Mon, Jan 15, 2018 at 4:16 PM, Mark Lacey <mark.lacey at apple.com <mailto:mark.lacey at apple.com>> wrote:
>> 
>> 
>>> On Jan 15, 2018, at 12:54 PM, Raj Barik <rkbarik at gmail.com <mailto:rkbarik at gmail.com>> wrote:
>>> 
>>> Mark,
>>> 
>>> Thanks a lot for quick reply.
>>>  
>>> Is there any reason this interface in SILInstruction should be private?
>>> void setDebugScope(SILBuilder &B, const SILDebugScope *DS);
>>> 
>>> In my case, I am splicing the old F into the new function NF. While splicing retains the debug scope, the new instruction (InitRef) that I am adding to NF is being created in some random scope (not F) even though I explicitly make Builder's debug scope point to F's. 
>> 
>> The assert you originally hit appears to indicate that the parentFunction of the debug scope for an instruction should be the same as the function the instruction is in. I am not very familiar with the requirements of our debug information and debug scopes, but this seems like a reasonable expectation.
>> 
>> I suggested looking at SILCloner because it is the primary way by which we clone functions, and clearly has to deal with debug scopes when it does so.
>> 
>> I’m not sure how much more help I can be on this matter, but perhaps someone more knowledgable can chime in.
>> 
>> Mark
>> 
>> 
>> 
>> 
>>> 
>>> Best,
>>> Raj
>>> 
>>> 
>>> 
>>> On Mon, Jan 15, 2018 at 9:52 AM, Mark Lacey <mark.lacey at apple.com <mailto:mark.lacey at apple.com>> wrote:
>>> I’d suggest looking at SILCloner.h as well as ScopeCloner in SILBasicBlock.cpp to see how they are dealing with debug scopes.
>>> 
>>> Mark
>>> 
>>> > On Jan 15, 2018, at 9:24 AM, Raj Barik via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>>> >
>>> > Hi,
>>> >
>>> > I am running into a debug scope SIL Verifier error when creating a new function (NF) from an existing one (F). Can someone point me where I am going wrong?
>>> >
>>> > NF = M.createFunction(...., F->getDebugScope());
>>> > SILBasicBlock *NFBody = NF->createBasicBlock();
>>> > SILBuilder NFBuilder(NFBody);
>>> > SILOpenedArchetypesTracker OpenedArchetypesTrackerNF(NF);
>>> > NFBuilder.setOpenedArchetypesTracker(&OpenedArchetypesTrackerNF);
>>> > NFBuilder.setCurrentDebugScope(NFBody->getParent()->getDebugScope());
>>> > ...
>>> > for (auto &param : params) { /* Assume all are generic types */
>>> >   auto GenericsSILType = ....
>>> >   auto NewArg = NFBody->createFunctionArgument(GenericSILType);
>>> >   auto Conformances = Mod->lookupConformance(...);
>>> >   auto *InitRef = NFBuilder.createInitExistentialRef( Loc, ArgDesc.Arg->getType(), NewArg->getType().getSwiftRValueType()->getCanonicalType(), NewArg, Conformances);
>>> >   ...
>>> > }
>>> >
>>> > The InitRef instruction created above runs into SIL verifier error:
>>> >
>>> > SIL verification failed: debug scope of instruction belongs to a different function: !DS || DS->getParentFunction() == I->getFunction()
>>> > Verifying instruction:
>>> >    %0 = argument of bb0 : $τ_0_0                 // user: %1
>>> > ->   %1 = init_existential_ref %0 : $τ_0_0 : $τ_0_0, $SomeProtocol // user: %2
>>> >
>>> > The SIL looks correct to me though.
>>> >
>>> > --Raj
>>> > _______________________________________________
>>> > swift-dev mailing list
>>> > swift-dev at swift.org <mailto:swift-dev at swift.org>
>>> > https://lists.swift.org/mailman/listinfo/swift-dev <https://lists.swift.org/mailman/listinfo/swift-dev>
>>> 
>>> 
>> 
>> 
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