[llvm] r190421 - Debug Info: create scope children DIEs when the scope DIE is not null.
David Blaikie
dblaikie at gmail.com
Tue Sep 10 14:30:49 PDT 2013
On Tue, Sep 10, 2013 at 2:17 PM, Eric Christopher <echristo at gmail.com>wrote:
> >> 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. :\
>
Yeah, I'm rather curious about this. Given that we don't have a list of
lexical scope children in their parent scope, the only reason a lexical
scope even stays alive is by virtue of its children (instructions,
variables, etc) staying alive within it - if all the children go away, the
lexical scope should be dropped or otherwise never be seen/reached.
>
> -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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