Add new merge-by-content Merge attribute for use by anonymous

constants and string literals which the linker should coalesce.

llvm-svn: 172495

8 files changed, 88 insertions, 17 deletions

diff --git a/lld/include/lld/Core/DefinedAtom.h b/lld/include/lld/Core/DefinedAtom.h
index 5c5b4acb47f..f3ab5434a1e 100644
--- a/lld/include/lld/Core/DefinedAtom.h
+++ b/lld/include/lld/Core/DefinedAtom.h
@@ -101,8 +101,9 @@ public:
     mergeAsWeak,            // is C++ inline definition that was not inlined,
                             // but address was not taken, so atom can be hidden
                             // by linker
-    mergeAsWeakAndAddressUsed // is C++ definition inline definition whose
+    mergeAsWeakAndAddressUsed,// is C++ definition inline definition whose
                               // address was taken.
+    mergeByContent          // merge with other constants with same content
   };
 
   enum ContentType {
diff --git a/lld/lib/Core/Resolver.cpp b/lld/lib/Core/Resolver.cpp
index 8b426fae87f..7e0d2e2895b 100644
--- a/lld/lib/Core/Resolver.cpp
+++ b/lld/lib/Core/Resolver.cpp
@@ -110,11 +110,8 @@ void Resolver::doDefinedAtom(const DefinedAtom &atom) {
   // add to list of known atoms
   _atoms.push_back(&atom);
 
-  // non-static atoms need extra handling
-  if (atom.scope() != DefinedAtom::scopeTranslationUnit) {
-    // tell symbol table about non-static atoms
-    _symbolTable.add(atom);
-  }
+  // tell symbol table 
+  _symbolTable.add(atom);
 
   if (_options.deadCodeStripping()) {
     // add to set of dead-strip-roots, all symbols that
diff --git a/lld/lib/Core/SymbolTable.cpp b/lld/lib/Core/SymbolTable.cpp
index b3fe8e8a50e..1c7ea99ff05 100644
--- a/lld/lib/Core/SymbolTable.cpp
+++ b/lld/lib/Core/SymbolTable.cpp
@@ -46,11 +46,16 @@ void SymbolTable::add(const AbsoluteAtom &atom) {
 }
 
 void SymbolTable::add(const DefinedAtom &atom) {
-  assert(atom.scope() != DefinedAtom::scopeTranslationUnit);
-  if ( !atom.name().empty() ) {
+  if (!atom.name().empty() && 
+      (atom.scope() != DefinedAtom::scopeTranslationUnit)) {
+    // Named atoms cannot be merged by content.
+    assert(atom.merge() != DefinedAtom::mergeByContent);
+    // Track named atoms that are not scoped to file (static).
     this->addByName(atom);
   }
-  else {
+  else if ( atom.merge() == DefinedAtom::mergeByContent ) {
+    // Named atoms cannot be merged by content.
+    assert(atom.name().empty());
     this->addByContent(atom);
   }
 }
@@ -123,6 +128,7 @@ static MergeResolution mergeSelect(DefinedAtom::Merge first,
 
 void SymbolTable::addByName(const Atom & newAtom) {
   StringRef name = newAtom.name();
+  assert(!name.empty());
   const Atom *existing = this->findByName(name);
   if (existing == nullptr) {
     // Name is not in symbol table yet, add it associate with this atom.
@@ -283,6 +289,8 @@ bool SymbolTable::AtomMappingInfo::isEqual(const DefinedAtom * const l,
 }
 
 void SymbolTable::addByContent(const DefinedAtom & newAtom) {
+  // Currently only read-only constants can be merged.
+  assert(newAtom.permissions() == DefinedAtom::permR__);
   AtomContentSet::iterator pos = _contentTable.find(&newAtom);
   if ( pos == _contentTable.end() ) {
     _contentTable.insert(&newAtom);
diff --git a/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp b/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp
index 0581c2e056a..310e8b41654 100644
--- a/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp
+++ b/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp
@@ -351,6 +351,7 @@ struct ScalarEnumerationTraits<lld::DefinedAtom::Merge> {
     io.enumCase(value, "as-weak",      lld::DefinedAtom::mergeAsWeak);
     io.enumCase(value, "as-addressed-weak", 
                                   lld::DefinedAtom::mergeAsWeakAndAddressUsed);
+    io.enumCase(value, "by-content",   lld::DefinedAtom::mergeByContent);
   }
 };
 
diff --git a/lld/test/constants-coalesce.objtxt b/lld/test/constants-coalesce.objtxt
new file mode 100644
index 00000000000..da388e50fe3
--- /dev/null
+++ b/lld/test/constants-coalesce.objtxt
@@ -0,0 +1,60 @@
+# RUN: lld-core %s | FileCheck %s
+
+#
+# Test that duplicate merge-by-content anonymous constants are coalesced
+# and non-mergable duplicate constants are not coalesced.
+#
+
+---
+defined-atoms:
+    - ref-name:          L4-byte
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03, 04 ]
+      
+    - ref-name:          L8-byte
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 23, 45, 67, 89, AB, CD, EF ]
+
+    - ref-name:          L1
+      type:              constant
+      content:           [ 01, 02 ]
+---
+defined-atoms:
+    - ref-name:          L1
+      type:              constant
+      content:           [ 01, 02 ]
+    - ref-name:          L2
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03, 04 ]
+---
+defined-atoms:
+    - ref-name:          L2
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 23, 45, 67, 89, AB, CD, EF ]
+    - ref-name:          L3
+      type:              constant
+      merge:             by-content
+      content:           [ 01, 02, 03 ]
+...
+
+# CHECK-NOT:   name:
+# CHECK:       type:       constant
+# CHECK:       content:    [ 01, 02, 03, 04 ]
+# CHECK:       merge:      by-content
+# CHECK:       type:       constant
+# CHECK:       content:    [ 01, 23, 45, 67, 89, AB, CD, EF ]
+# CHECK:       merge:      by-content
+# CHECK:       type:       constant
+# CHECK:       content:    [ 01, 02 ]
+# CHECK:       type:       constant
+# CHECK:       content:    [ 01, 02 ]
+# CHECK:       type:       constant
+# CHECK:       content:    [ 01, 02, 03 ]
+# CHECK:       merge:      by-content
+# CHECK:       ...
+
+
diff --git a/lld/test/cstring-coalesce.objtxt b/lld/test/cstring-coalesce.objtxt
index 5b37acca5c7..5723299c110 100644
--- a/lld/test/cstring-coalesce.objtxt
+++ b/lld/test/cstring-coalesce.objtxt
@@ -7,31 +7,35 @@
 ---
 defined-atoms:
     - ref-name:          L0
-      scope:             hidden
       type:              c-string
+      merge:             by-content
       content:           [ 68, 65, 6c, 6c, 6f, 00 ]
       
     - ref-name:          L1
-      scope:             hidden
       type:              c-string
+      merge:             by-content
       content:           [ 74, 68, 65, 72, 65, 00 ]
 ---
 defined-atoms:
     - ref-name:          L2
-      scope:             hidden
       type:              c-string
+      merge:             by-content
       content:           [ 68, 65, 6c, 6c, 6f, 00 ]
 ---
 defined-atoms:
     - ref-name:          L2
-      scope:             hidden
       type:              c-string
+      merge:             by-content
       content:           [ 74, 68, 65, 72, 65, 00 ]
 ...
 
+# CHECK-NOT:   name:
 # CHECK:       type:       c-string
 # CHECK:       content:    [ 68, 65, 6C, 6C, 6F, 00 ]
+# CHECK:       merge:      by-content
 # CHECK:       type:       c-string
 # CHECK:       content:    [ 74, 68, 65, 72, 65, 00 ]
-# CHECK-NOT:   name:
+# CHECK:       merge:      by-content
 # CHECK:       ...
+
+
diff --git a/lld/test/darwin/hello-world.objtxt b/lld/test/darwin/hello-world.objtxt
index 3b99933eb33..0d96c0746b0 100644
--- a/lld/test/darwin/hello-world.objtxt
+++ b/lld/test/darwin/hello-world.objtxt
@@ -21,8 +21,8 @@ defined-atoms:
         target:          _printf
 
     - ref-name:          LC1
-      scope:             hidden
       type:              c-string
+      merge:             by-content
       content:           [ 68, 65, 6C, 6C, 6F, 0A, 00 ]
 
 shared-library-atoms:     
diff --git a/lld/test/fixups-unnamed.objtxt b/lld/test/fixups-unnamed.objtxt
index 20cf373580e..2c3d7aa09d9 100644
--- a/lld/test/fixups-unnamed.objtxt
+++ b/lld/test/fixups-unnamed.objtxt
@@ -20,13 +20,13 @@ defined-atoms:
   
 
     - ref-name:          LC1
-      scope:             hidden
       type:              c-string
+      merge:             by-content
       content:           [ 68, 65, 6c, 6c, 6f, 00 ]
 
     - ref-name:          LC2
-      scope:             hidden
       type:              c-string
+      merge:             by-content
       content:           [ 74, 68, 65, 72, 65, 00 ]