[PATCH] Select new undefined atom rather than old one if other conditions are the same.

[Rui Ueyama]

> __lseek. When the linker tries to resolve _read, it supposed to read the
> file
>

There's a typo in this line: s/_read/_lseek/


> from OLDNAMES.LIB and use the new fallback from the file. Currently LLD
> cannot
> handle such case because duplicate undefined atoms with the same
> attributes are
> ignored.
>
> http://llvm-reviews.chandlerc.com/D2161
>
> Files:
>   lib/Core/SymbolTable.cpp
>   test/core/undef-weak-coalesce.objtxt
>
> Index: lib/Core/SymbolTable.cpp
> ===================================================================
> --- lib/Core/SymbolTable.cpp
> +++ lib/Core/SymbolTable.cpp
> @@ -178,20 +178,34 @@
>              dyn_cast<UndefinedAtom>(&newAtom);
>            assert(existingUndef != nullptr);
>            assert(newUndef != nullptr);
> -          if ( existingUndef->canBeNull() == newUndef->canBeNull() ) {
> -            useNew = false;
> +          if (existingUndef->canBeNull() != newUndef->canBeNull() &&
> +              _context.warnIfCoalesableAtomsHaveDifferentCanBeNull()) {
> +            // FIXME: need diagonstics interface for writing warning
> messages
> +            llvm::errs() << "lld warning: undefined symbol "
> +                         << existingUndef->name()
> +                         << " has different weakness in "
> +                         << existingUndef->file().path()
> +                         << " and in "
> +                         << newUndef->file().path();
>            }
> -          else {
> -            if (_context.warnIfCoalesableAtomsHaveDifferentCanBeNull()) {
> -              // FIXME: need diagonstics interface for writing warning
> messages
> -              llvm::errs() << "lld warning: undefined symbol "
> -                           << existingUndef->name()
> -                           << " has different weakness in "
> -                           << existingUndef->file().path()
> -                           << " and in "
> -                           << newUndef->file().path();
> -            }
> -            useNew = (newUndef->canBeNull() < existingUndef->canBeNull());
> +          useNew = (newUndef->canBeNull() <= existingUndef->canBeNull());
> +
> +          // Warn if the fallback atom is being overriden.
> +          const UndefinedAtom *existingFallback =
> existingUndef->fallback();
> +          if (useNew && existingFallback) {
> +            const UndefinedAtom *newFallback = newUndef->fallback();
> +            if (!newFallback) {
> +              llvm::errs() << "lld warning: new undefined atom removes
> the "
> +                           << "existing fallback atom "
> +                           << existingUndef->name() << " ("
> +                           << existingFallback->name() << ")";
> +            } else if (existingFallback->name() != newFallback->name())
> +              llvm::errs() << "lld warning: new undefined atom "
> +                           << newUndef->name() << " ("
> +                           << newFallback->name() << ")"
> +                           << " shadows the existing fallback atom "
> +                           << existingUndef->name() << " ("
> +                           << existingFallback->name() << ")";
>            }
>          }
>          break;
> Index: test/core/undef-weak-coalesce.objtxt
> ===================================================================
> --- test/core/undef-weak-coalesce.objtxt
> +++ test/core/undef-weak-coalesce.objtxt
> @@ -8,86 +8,66 @@
>  undefined-atoms:
>      - name:              regular_func
>        can-be-null:       never
> -
>      - name:              weak_import_func
>        can-be-null:       at-runtime
> -
>      - name:              weak_func
>        can-be-null:       at-buildtime
> -
>      - name:              bar1
>        can-be-null:       never
> -
>      - name:              bar2
>        can-be-null:       at-runtime
> -
>      - name:              bar3
>        can-be-null:       at-buildtime
> -
>      - name:              bar4
>        can-be-null:       never
> -
>      - name:              bar5
>        can-be-null:       at-runtime
> -
>      - name:              bar6
>        can-be-null:       at-buildtime
> -
>      - name:              bar7
>        can-be-null:       never
> -
>      - name:              bar8
>        can-be-null:       at-runtime
> -
>      - name:              bar9
>        can-be-null:       at-buildtime
> -
>  ---
>  undefined-atoms:
>      - name:              bar1
>        can-be-null:       never
> -
>      - name:              bar2
>        can-be-null:       at-runtime
> -
>      - name:              bar3
>        can-be-null:       at-buildtime
> -
>      - name:              bar4
>        can-be-null:       at-runtime
> -
>      - name:              bar5
>        can-be-null:       at-buildtime
> -
>      - name:              bar6
>        can-be-null:       never
> -
>      - name:              bar7
>        can-be-null:       at-buildtime
> -
>      - name:              bar8
>        can-be-null:       never
> -
>      - name:              bar9
>        can-be-null:       at-runtime
>  ...
>
> -# CHECK:   - name:       regular_func
> -# CHECK:   - name:       weak_import_func
> -# CHECK:     can-be-null:  at-runtime
> -# CHECK:   - name:       weak_func
> -# CHECK:     can-be-null:  at-buildtime
> -# CHECK:   - name:       bar1
> -# CHECK:   - name:       bar2
> -# CHECK:     can-be-null:  at-runtime
> -# CHECK:   - name:       bar3
> -# CHECK:     can-be-null:  at-buildtime
> -# CHECK:   - name:       bar4
> -# CHECK:   - name:       bar5
> -# CHECK:     can-be-null:  at-runtime
> -# CHECK:   - name:       bar7
> -# CHECK:   - name:       bar6
> -# CHECK:   - name:       bar8
> -# CHECK:   - name:       bar9
> -# CHECK:     can-be-null:  at-runtime
> -# CHECK:       ...
> +# CHECK:        - name:       regular_func
> +# CHECK-NEXT:   - name:       weak_import_func
> +# CHECK-NEXT:     can-be-null:  at-runtime
> +# CHECK-NEXT:   - name:       weak_func
> +# CHECK-NEXT:     can-be-null:  at-buildtime
> +# CHECK-NEXT:   - name:       bar4
> +# CHECK-NEXT:   - name:       bar5
> +# CHECK-NEXT:     can-be-null:  at-runtime
> +# CHECK-NEXT:   - name:       bar7
> +# CHECK-NEXT:   - name:       bar1
> +# CHECK-NEXT:   - name:       bar2
> +# CHECK-NEXT:     can-be-null:  at-runtime
> +# CHECK-NEXT:   - name:       bar3
> +# CHECK-NEXT:     can-be-null:  at-buildtime
> +# CHECK-NEXT:   - name:       bar6
> +# CHECK-NEXT:   - name:       bar8
> +# CHECK-NEXT:   - name:       bar9
> +# CHECK-NEXT:     can-be-null:  at-runtime
> +# CHECK-NEXT:       ...
>
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