[PATCH] Reload undefined atoms to use possibly new undefines.

[Rui Ueyama]

  Reworked to implement the correct semantics of Weak Externals. Updated the commit message. Also added tests.

http://llvm-reviews.chandlerc.com/D2162

CHANGE SINCE LAST DIFF
  http://llvm-reviews.chandlerc.com/D2162?vs=5585&id=5645#toc

Files:
  lib/Core/Resolver.cpp
  test/core/undef-fallback.objtxt
  test/core/undef-weak-coalesce.objtxt
  test/pecoff/weak-external.test

Index: lib/Core/Resolver.cpp
===================================================================
--- lib/Core/Resolver.cpp
+++ lib/Core/Resolver.cpp
@@ -83,6 +83,16 @@
   for (const UndefinedAtom *undefAtom : file.undefined()) {
     doUndefinedAtom(*undefAtom);
     resolverState |= StateNewUndefinedAtoms;
+
+    // If the undefined symbol has an alternative name, try to resolve the
+    // symbol with the name to give it a second chance. This feature is used for
+    // COFF "weak external" symbol.
+    if (!_symbolTable.isDefined(undefAtom->name())) {
+      if (const UndefinedAtom *fallbackAtom = undefAtom->fallback()) {
+        doUndefinedAtom(*fallbackAtom);
+        _symbolTable.addReplacement(undefAtom, fallbackAtom);
+      }
+    }
   }
   for (const SharedLibraryAtom *shlibAtom : file.sharedLibrary()) {
     doSharedLibraryAtom(*shlibAtom);
@@ -108,15 +118,6 @@
       // load for previous undefine may also have loaded this undefine
       if (!_symbolTable.isDefined(undefName))
         callback(undefName, false);
-      // If the undefined symbol has an alternative name, try to resolve the
-      // symbol with the name to give it a second chance. This feature is used
-      // for COFF "weak external" symbol.
-      if (!_symbolTable.isDefined(undefName)) {
-        if (const UndefinedAtom *fallbackUndefAtom = undefAtom->fallback()) {
-          _symbolTable.addReplacement(undefAtom, fallbackUndefAtom);
-          _symbolTable.add(*fallbackUndefAtom);
-        }
-      }
     }
     // search libraries for overrides of common symbols
     if (searchForOverrides) {
Index: test/core/undef-fallback.objtxt
===================================================================
--- test/core/undef-fallback.objtxt
+++ test/core/undef-fallback.objtxt
@@ -5,14 +5,33 @@
 
 ---
 defined-atoms:
-  - name: bar
-    type: code
+  - name: def1
+    scope: global
 
 undefined-atoms:
-  - name: foo
+  - name: undef1
     fallback:
-      name: bar
+      name: fallback1
+  - name: undef2
+    fallback:
+      name: fallback2
+---
+defined-atoms:
+  - name: fallback1
+
+undefined-atoms:
+  - name: def1
+    fallback:
+      name: fallback3
 ...
 
 # CHECK:      defined-atoms:
-# CHECK-NEXT:   - name: bar
+# CHECK-NEXT:   - name:            def1
+# CHECK-NEXT:     scope:           global
+# CHECK-NEXT:   - name:            fallback1
+# CHECK-NEXT:     ref-name:        fallback1
+# CHECK-NEXT: undefined-atoms:
+# CHECK-NEXT:   - name:            fallback1
+# CHECK-NEXT:   - name:            fallback2
+
+# CHECK-NOT:    - name:            fallback3
\ No newline at end of file
Index: test/core/undef-weak-coalesce.objtxt
===================================================================
--- test/core/undef-weak-coalesce.objtxt
+++ test/core/undef-weak-coalesce.objtxt
@@ -1,5 +1,4 @@
-# RUN: lld -core %s 2> %t.err | FileCheck %s
-# RUN: FileCheck -check-prefix=ERROR %s < %t.err
+# RUN: lld -core %s | FileCheck %s
 
 #
 # Test that undefined symbols preserve their attributes and merge properly
@@ -29,12 +28,8 @@
       can-be-null:       never
     - name:              bar8
       can-be-null:       at-runtime
-      fallback:
-        name: baz1
     - name:              bar9
       can-be-null:       at-buildtime
-      fallback:
-        name: baz2
 ---
 undefined-atoms:
     - name:              bar1
@@ -55,8 +50,6 @@
       can-be-null:       never
     - name:              bar9
       can-be-null:       at-runtime
-      fallback:
-        name: baz3
 ...
 
 # CHECK:       - name:            regular_func
@@ -77,7 +70,3 @@
 # CHECK-NEXT:  - name:            bar8
 # CHECK-NEXT:  - name:            bar9
 # CHECK-NEXT:    can-be-null:     at-runtime
-# CHECK-NEXT:    fallback:
-# CHECK-NEXT:      name:            baz3
-
-# ERROR: undefined symbol bar9 has different fallback: baz2 in and baz3 in
Index: test/pecoff/weak-external.test
===================================================================
--- test/pecoff/weak-external.test
+++ test/pecoff/weak-external.test
@@ -4,6 +4,6 @@
 # RUN:    /entry:fn -- %t.obj %p/Inputs/static.lib 2> %t2.out
 # RUN: FileCheck %s < %t2.out
 
-CHECK-NOT: _no_such_symbol1
+CHECK: _no_such_symbol1
 CHECK-NOT: _no_such_symbol2
 CHECK: _no_such_symbol3
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