Things like the existence of extra artificial entries do seem appropriate for putting under "tuning" control.
I suppose I should ping/refresh the tuning patch… been letting it slide due to a particularly snarky merge and needing to get the depfile thing sorted out for an imminent release. I'll be back on it Real Soon Now. --paulr From: [email protected] [mailto:[email protected]] On Behalf Of Eric Christopher Sent: Wednesday, April 29, 2015 10:04 AM To: Adrian Prantl; David Blaikie Cc: llvm cfe Subject: Re: r236059 - Debug Info: Represent local anonymous unions as anonymous unions On Wed, Apr 29, 2015 at 9:58 AM Eric Christopher <[email protected]<mailto:[email protected]>> wrote: On Wed, Apr 29, 2015 at 8:20 AM Adrian Prantl <[email protected]<mailto:[email protected]>> wrote: > On Apr 28, 2015, at 6:26 PM, David Blaikie > <[email protected]<mailto:[email protected]>> wrote: > > > > On Tue, Apr 28, 2015 at 4:01 PM, Adrian Prantl > <[email protected]<mailto:[email protected]>> wrote: > Author: adrian > Date: Tue Apr 28 18:01:24 2015 > New Revision: 236059 > > URL: http://llvm.org/viewvc/llvm-project?rev=236059&view=rev > Log: > Debug Info: Represent local anonymous unions as anonymous unions > in the debug info. This patch deletes a hack that emits the members > of local anonymous unions as local variables. > > Besides being morally wrong, the existing representation using local > variables breaks internal assumptions about the local variables' storage > size. > > Compiling > > ``` > void fn1() { > union { > int i; > char c; > }; > i = c; > } > > ``` > > with -g -O3 -verify will cause the verifier to fail after SROA splits > the 32-bit storage for the "local variable" c into two pieces because the > second piece is clearly outside the 8-bit range that is expected for a > variable of type char. Given the choice I'd rather fix the debug > representation than weaken the verifier. > > Debuggers generally already know how to deal with anonymous unions when > they are members of C++ record types, but they may have problems finding > the local anonymous struct members in the expression evaluator. > > Seems we're not so lucky: > http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/21650/steps/gdb-75-check/logs/gdb.cp__anon-union.exp > > Could you revert & I'll look into getting you a reduced test > case/demonstration of the issue? (can you run GDB 7.5? Perhaps a simple test > case would demonstrate the issue if you're lucky, otherwise I can reduce one > from the failing test case) I reverted the commit in r236110. I probably won’t need a reduction — my guess from the log is that gdb expects a local variable to be present. My suggestion is to emit local artificial shadow variables and then weaken the Verifier to not verify artificial variables. In a next step, we could use the new debugger tuning target feature to make the artificial local variables and the weakened verifier a gdb-specific behavior, file a bug against gdb, and eventually remove it altogether. FWIW I don't want to use the "tuning" parameters to also affect correctness. OK. Dave and I debated this a little in person, here's a proposal: by default it will have the gdb specific behavior, but if you're tuning for lldb (or any other debugger I guess?) it won't be there. Thoughts? -eric -eric -- adrian > > > rdar://problem/20730771 > > Modified: > cfe/trunk/lib/CodeGen/CGDebugInfo.cpp > cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp > > Modified: cfe/trunk/lib/CodeGen/CGDebugInfo.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.cpp?rev=236059&r1=236058&r2=236059&view=diff > ============================================================================== > --- cfe/trunk/lib/CodeGen/CGDebugInfo.cpp (original) > +++ cfe/trunk/lib/CodeGen/CGDebugInfo.cpp Tue Apr 28 18:01:24 2015 > @@ -2835,31 +2835,6 @@ void CGDebugInfo::EmitDeclare(const VarD > return; > } else if (isa<VariableArrayType>(VD->getType())) > Expr.push_back(llvm::dwarf::DW_OP_deref); > - } else if (const RecordType *RT = dyn_cast<RecordType>(VD->getType())) { > - // If VD is an anonymous union then Storage represents value for > - // all union fields. > - const RecordDecl *RD = cast<RecordDecl>(RT->getDecl()); > - if (RD->isUnion() && RD->isAnonymousStructOrUnion()) { > - for (const auto *Field : RD->fields()) { > - llvm::MDType *FieldTy = getOrCreateType(Field->getType(), Unit); > - StringRef FieldName = Field->getName(); > - > - // Ignore unnamed fields. Do not ignore unnamed records. > - if (FieldName.empty() && !isa<RecordType>(Field->getType())) > - continue; > - > - // Use VarDecl's Tag, Scope and Line number. > - auto *D = DBuilder.createLocalVariable( > - Tag, Scope, FieldName, Unit, Line, FieldTy, > - CGM.getLangOpts().Optimize, Flags, ArgNo); > - > - // Insert an llvm.dbg.declare into the current block. > - DBuilder.insertDeclare(Storage, D, DBuilder.createExpression(Expr), > - llvm::DebugLoc::get(Line, Column, Scope), > - Builder.GetInsertBlock()); > - } > - return; > - } > } > > // Create the descriptor for the variable. > > Modified: cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp?rev=236059&r1=236058&r2=236059&view=diff > ============================================================================== > --- cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp (original) > +++ cfe/trunk/test/CodeGenCXX/debug-info-anon-union-vars.cpp Tue Apr 28 > 18:01:24 2015 > @@ -21,8 +21,26 @@ int test_it() { > return (c == 1); > } > > +// This is not necessary (and actually harmful because it breaks IR > assumptions) > +// for local variables. > +void foo() { > + union { > + int i; > + char c; > + }; > + i = 8; > +} > + > // CHECK: [[FILE:.*]] = !MDFile(filename: > "{{.*}}debug-info-anon-union-vars.cpp", > // CHECK: !MDGlobalVariable(name: "c",{{.*}} file: [[FILE]], line: 6,{{.*}} > isLocal: true, isDefinition: true > // CHECK: !MDGlobalVariable(name: "d",{{.*}} file: [[FILE]], line: 6,{{.*}} > isLocal: true, isDefinition: true > // CHECK: !MDGlobalVariable(name: "a",{{.*}} file: [[FILE]], line: 6,{{.*}} > isLocal: true, isDefinition: true > // CHECK: !MDGlobalVariable(name: "b",{{.*}} file: [[FILE]], line: 6,{{.*}} > isLocal: true, isDefinition: true > +// CHECK: !MDLocalVariable( > +// CHECK-NOT: name: > +// CHECK: type: ![[UNION:[0-9]+]] > +// CHECK: ![[UNION]] = !MDCompositeType(tag: DW_TAG_union_type, > +// CHECK-NOT: name: > +// CHECK: elements > +// CHECK: !MDDerivedType(tag: DW_TAG_member, name: "i", scope: ![[UNION]], > +// CHECK: !MDDerivedType(tag: DW_TAG_member, name: "c", scope: ![[UNION]], > > > _______________________________________________ > cfe-commits mailing list > [email protected]<mailto:[email protected]> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits > _______________________________________________ cfe-commits mailing list [email protected]<mailto:[email protected]> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
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