[llvm] r190421 - Debug Info: create scope children DIEs when the scope DIE is not null.
Eric Christopher
echristo at gmail.com
Tue Sep 10 14:17:19 PDT 2013
>> Testcase? How did you see this?
>
> This should not affect functionality :)
Oh good. I was hoping not. How did you come across this? I'm curious.
> It basically swaps the order of creation of Scope DIE vs. creation of
> children.
>
Yeah. It could use a lot more documentation.
> In the process, we removed an early exit which only captures some cases of
> creating dangling children.
> - // Early return to avoid creating dangling variable|scope DIEs.
> - if (!Scope->getInlinedAt() && DS.isSubprogram() &&
> Scope->isAbstractScope() &&
> - !TheCU->getDIE(DS))
> - return NULL;
>
> Creation of unused children then removing them are not efficient and it may
> cause problems if a member
> of DwarfDebug or CompileUnit holds a reference to the deleted DIE.
>
Makes sense, but I think only if you actually create them :)
>>
>>
>> For some of the patch:
>>
>> +bool DwarfDebug::isLexicalScopeDIENull(LexicalScope *Scope) {
>> + if (Scope->isAbstractScope())
>>
>> Needs a block comment.
>
> I have comments at the header file, I will copy it over to the source file.
Please be more detailed than in the header file.
>>
>>
>> + SmallVectorImpl<InsnRange>::const_iterator RI = Ranges.begin();
>> + MCSymbol *End = getLabelAfterInsn(RI->second);
>> + return !End;
>>
>> Where does this show up?
>
> I write up isLexicalScopeDIENull from constructLexicalScopeDIE.
> constructLexicalScopeDIE returns null
> when End is null. Is that what you are asking?
>
Yep. I'm still wondering where this shows up. :\
-eric
> Thanks,
> Manman
>>
>>
>> -eric
>>
>>
>> On Tue, Sep 10, 2013 at 11:40 AM, Manman Ren <manman.ren at gmail.com> wrote:
>> > Author: mren
>> > Date: Tue Sep 10 13:40:41 2013
>> > New Revision: 190421
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=190421&view=rev
>> > Log:
>> > Debug Info: create scope children DIEs when the scope DIE is not null.
>> >
>> > We try to create the scope children DIEs after we create the scope DIE.
>> > But
>> > to avoid emitting empty lexical block DIE, we first check whether a
>> > scope
>> > DIE is going to be null, then create the scope children if it is not
>> > null.
>> > From the number of children, we decide whether to actually create the
>> > scope DIE.
>> >
>> > This patch also removes an early exit which checks for a special
>> > condition.
>> > It also removes deletion of un-used children DIEs that are generated
>> > because we used to generate children DIEs before the scope DIE.
>> >
>> > Deletion of un-used children DIEs may cause problem because we sometimes
>> > keep
>> > created DIEs in a member variable of a CU.
>> >
>> > Modified:
>> > llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
>> > llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.h
>> >
>> > Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp?rev=190421&r1=190420&r2=190421&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (original)
>> > +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp Tue Sep 10 13:40:41
>> > 2013
>> > @@ -424,18 +424,34 @@ DIE *DwarfDebug::updateSubprogramScopeDI
>> > return SPDie;
>> > }
>> >
>> > +bool DwarfDebug::isLexicalScopeDIENull(LexicalScope *Scope) {
>> > + if (Scope->isAbstractScope())
>> > + return false;
>> > +
>> > + const SmallVectorImpl<InsnRange> &Ranges = Scope->getRanges();
>> > + if (Ranges.empty())
>> > + return true;
>> > +
>> > + if (Ranges.size() > 1)
>> > + return false;
>> > +
>> > + SmallVectorImpl<InsnRange>::const_iterator RI = Ranges.begin();
>> > + MCSymbol *End = getLabelAfterInsn(RI->second);
>> > + return !End;
>> > +}
>> > +
>> > // Construct new DW_TAG_lexical_block for this scope and attach
>> > // DW_AT_low_pc/DW_AT_high_pc labels.
>> > DIE *DwarfDebug::constructLexicalScopeDIE(CompileUnit *TheCU,
>> > LexicalScope *Scope) {
>> > + if (isLexicalScopeDIENull(Scope))
>> > + return 0;
>> > +
>> > DIE *ScopeDIE = new DIE(dwarf::DW_TAG_lexical_block);
>> > if (Scope->isAbstractScope())
>> > return ScopeDIE;
>> >
>> > const SmallVectorImpl<InsnRange> &Ranges = Scope->getRanges();
>> > - if (Ranges.empty())
>> > - return 0;
>> > -
>> > // If we have multiple ranges, emit them into the range section.
>> > if (Ranges.size() > 1) {
>> > // .debug_range section has not been laid out yet. Emit offset in
>> > @@ -460,8 +476,7 @@ DIE *DwarfDebug::constructLexicalScopeDI
>> > SmallVectorImpl<InsnRange>::const_iterator RI = Ranges.begin();
>> > MCSymbol *Start = getLabelBeforeInsn(RI->first);
>> > MCSymbol *End = getLabelAfterInsn(RI->second);
>> > -
>> > - if (End == 0) return 0;
>> > + assert(End && "End label should not be null!");
>> >
>> > assert(Start->isDefined() && "Invalid starting label for an inlined
>> > scope!");
>> > assert(End->isDefined() && "Invalid end label for an inlined
>> > scope!");
>> > @@ -540,19 +555,9 @@ DIE *DwarfDebug::constructInlinedScopeDI
>> > return ScopeDIE;
>> > }
>> >
>> > -// Construct a DIE for this scope.
>> > -DIE *DwarfDebug::constructScopeDIE(CompileUnit *TheCU, LexicalScope
>> > *Scope) {
>> > - if (!Scope || !Scope->getScopeNode())
>> > - return NULL;
>> > -
>> > - DIScope DS(Scope->getScopeNode());
>> > - // Early return to avoid creating dangling variable|scope DIEs.
>> > - if (!Scope->getInlinedAt() && DS.isSubprogram() &&
>> > Scope->isAbstractScope() &&
>> > - !TheCU->getDIE(DS))
>> > - return NULL;
>> > -
>> > - SmallVector<DIE *, 8> Children;
>> > - DIE *ObjectPointer = NULL;
>> > +DIE *DwarfDebug::createScopeChildrenDIE(CompileUnit *TheCU,
>> > LexicalScope *Scope,
>> > + SmallVectorImpl<DIE*>
>> > &Children) {
>> > + DIE *ObjectPointer = NULL;
>> >
>> > // Collect arguments for current function.
>> > if (LScopes.isCurrentFunctionScope(Scope))
>> > @@ -576,6 +581,20 @@ DIE *DwarfDebug::constructScopeDIE(Compi
>> > for (unsigned j = 0, M = Scopes.size(); j < M; ++j)
>> > if (DIE *Nested = constructScopeDIE(TheCU, Scopes[j]))
>> > Children.push_back(Nested);
>> > + return ObjectPointer;
>> > +}
>> > +
>> > +// Construct a DIE for this scope.
>> > +DIE *DwarfDebug::constructScopeDIE(CompileUnit *TheCU, LexicalScope
>> > *Scope) {
>> > + if (!Scope || !Scope->getScopeNode())
>> > + return NULL;
>> > +
>> > + DIScope DS(Scope->getScopeNode());
>> > +
>> > + SmallVector<DIE *, 8> Children;
>> > + DIE *ObjectPointer = NULL;
>> > + bool ChildrenCreated = false;
>> > +
>> > DIE *ScopeDIE = NULL;
>> > if (Scope->getInlinedAt())
>> > ScopeDIE = constructInlinedScopeDIE(TheCU, Scope);
>> > @@ -591,6 +610,12 @@ DIE *DwarfDebug::constructScopeDIE(Compi
>> > ScopeDIE = updateSubprogramScopeDIE(TheCU, DS);
>> > }
>> > else {
>> > + if (isLexicalScopeDIENull(Scope))
>> > + return NULL;
>> > + // We create children only when we know the scope DIE is not going
>> > to be
>> > + // null.
>> > + ObjectPointer = createScopeChildrenDIE(TheCU, Scope, Children);
>> > + ChildrenCreated = true;
>> > // There is no need to emit empty lexical block DIE.
>> > std::pair<ImportedEntityMap::const_iterator,
>> > ImportedEntityMap::const_iterator> Range =
>> > std::equal_range(
>> > @@ -600,15 +625,19 @@ DIE *DwarfDebug::constructScopeDIE(Compi
>> > if (Children.empty() && Range.first == Range.second)
>> > return NULL;
>> > ScopeDIE = constructLexicalScopeDIE(TheCU, Scope);
>> > + assert(ScopeDIE && "Scope DIE should not be null.");
>> > for (ImportedEntityMap::const_iterator i = Range.first; i !=
>> > Range.second;
>> > ++i)
>> > constructImportedEntityDIE(TheCU, i->second, ScopeDIE);
>> > }
>> >
>> > if (!ScopeDIE) {
>> > - std::for_each(Children.begin(), Children.end(), deleter<DIE>);
>> > + assert(Children.empty() &&
>> > + "We create children only when the scope DIE is not null.");
>> > return NULL;
>> > }
>> > + if (!ChildrenCreated)
>> > + ObjectPointer = createScopeChildrenDIE(TheCU, Scope, Children);
>> >
>> > // Add children
>> > for (SmallVectorImpl<DIE *>::iterator I = Children.begin(),
>> >
>> > Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.h
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.h?rev=190421&r1=190420&r2=190421&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.h (original)
>> > +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.h Tue Sep 10 13:40:41
>> > 2013
>> > @@ -469,6 +469,9 @@ private:
>> > /// \brief Construct new DW_TAG_lexical_block for this scope and
>> > /// attach DW_AT_low_pc/DW_AT_high_pc labels.
>> > DIE *constructLexicalScopeDIE(CompileUnit *TheCU, LexicalScope
>> > *Scope);
>> > + /// A helper function to check whether the DIE for a given Scope is
>> > going
>> > + /// to be null.
>> > + bool isLexicalScopeDIENull(LexicalScope *Scope);
>> >
>> > /// \brief This scope represents inlined body of a function.
>> > Construct
>> > /// DIE to represent this concrete inlined copy of the function.
>> > @@ -476,6 +479,9 @@ private:
>> >
>> > /// \brief Construct a DIE for this scope.
>> > DIE *constructScopeDIE(CompileUnit *TheCU, LexicalScope *Scope);
>> > + /// A helper function to create children of a Scope DIE.
>> > + DIE *createScopeChildrenDIE(CompileUnit *TheCU, LexicalScope *Scope,
>> > + SmallVectorImpl<DIE*> &Children);
>> >
>> > /// \brief Emit initial Dwarf sections with a label at the start of
>> > each one.
>> > void emitSectionLabels();
>> >
>> >
>> > _______________________________________________
>> > llvm-commits mailing list
>> > llvm-commits at cs.uiuc.edu
>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
>
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