[LTO] Add function alias as function instead of data (#112599)

On AIX, for undefined functions, only the dotnamed symbols (the address
of the function) are generated after linking (i.e., no named function
symbol is generated).
 
Currently, all alias symbols are added as defined data symbols when
parsing symbols in LTOModule (the Link Time Optimization library used by
linker to optimization code at link time). On AIX, if the function alias
is used in the native object, and only its dotnamed symbol is generated,
the linker will have problem to match the dotnamed symbol from the
native object and the defined symbol marked as data from the bitcode at
LTO linktime.
 
This patch is to add function alias as function instead of data.

Author: scui-ibm

llvm/include/llvm/LTO/legacy/LTOModule.h

@@ -195,7 +195,7 @@ struct LTOModule {
 
   /// Add a function symbol as defined to the list.
   void addDefinedFunctionSymbol(ModuleSymbolTable::Symbol Sym);
-  void addDefinedFunctionSymbol(StringRef Name, const Function *F);
+  void addDefinedFunctionSymbol(StringRef Name, const GlobalValue *F);
 
   /// Add a global symbol from module-level ASM to the defined list.
   void addAsmGlobalSymbol(StringRef, lto_symbol_attributes scope);

llvm/lib/LTO/LTOModule.cpp

@@ -406,11 +406,16 @@ void LTOModule::addDefinedFunctionSymbol(ModuleSymbolTable::Symbol Sym) {
     Buffer.c_str();
   }
 
-  const Function *F = cast<Function>(cast<GlobalValue *>(Sym));
-  addDefinedFunctionSymbol(Buffer, F);
+  auto *GV = cast<GlobalValue *>(Sym);
+  assert((isa<Function>(GV) ||
+          (isa<GlobalAlias>(GV) &&
+           isa<Function>(cast<GlobalAlias>(GV)->getAliasee()))) &&
+         "Not function or function alias");
+
+  addDefinedFunctionSymbol(Buffer, GV);
 }
 
-void LTOModule::addDefinedFunctionSymbol(StringRef Name, const Function *F) {
+void LTOModule::addDefinedFunctionSymbol(StringRef Name, const GlobalValue *F) {
   // add to list of defined symbols
   addDefinedSymbol(Name, F, true);
 }
@@ -611,7 +616,11 @@ void LTOModule::parseSymbols() {
     }
 
     assert(isa<GlobalAlias>(GV));
-    addDefinedDataSymbol(Sym);
+
+    if (isa<Function>(cast<GlobalAlias>(GV)->getAliasee()))
+      addDefinedFunctionSymbol(Sym);
+    else
+      addDefinedDataSymbol(Sym);
   }
 
   // make symbols for all undefines

llvm/test/LTO/PowerPC/list-symbol.ll

@@ -0,0 +1,16 @@
+; RUN: llvm-as < %s > %t
+; RUN: llvm-lto -list-symbols-only %t | FileCheck %s
+; REQUIRES: default_triple
+
+; CHECK-DAG: v    { data defined default }
+; CHECK-DAG: va    { data defined default alias }
+; CHECK-DAG: f    { function defined default }
+; CHECK-DAG: fa    { function defined default alias }
+
+@v = global i32 0
+@va = alias i32, ptr @v
+@fa = alias void (ptr), ptr @f
+
+define void @f() {
+  ret void
+}

llvm/tools/llvm-lto/llvm-lto.cpp

@@ -407,6 +407,64 @@ static void printIndexStats() {
   }
 }
 
+/// Print the lto symbol attributes.
+static void printLTOSymbolAttributes(lto_symbol_attributes Attrs) {
+  outs() << "{ ";
+  unsigned Permission = Attrs & LTO_SYMBOL_PERMISSIONS_MASK;
+  switch (Permission) {
+  case LTO_SYMBOL_PERMISSIONS_CODE:
+    outs() << "function ";
+    break;
+  case LTO_SYMBOL_PERMISSIONS_DATA:
+    outs() << "data ";
+    break;
+  case LTO_SYMBOL_PERMISSIONS_RODATA:
+    outs() << "constant ";
+    break;
+  }
+  unsigned Definition = Attrs & LTO_SYMBOL_DEFINITION_MASK;
+  switch (Definition) {
+  case LTO_SYMBOL_DEFINITION_REGULAR:
+    outs() << "defined ";
+    break;
+  case LTO_SYMBOL_DEFINITION_TENTATIVE:
+    outs() << "common ";
+    break;
+  case LTO_SYMBOL_DEFINITION_WEAK:
+    outs() << "weak ";
+    break;
+  case LTO_SYMBOL_DEFINITION_UNDEFINED:
+    outs() << "extern ";
+    break;
+  case LTO_SYMBOL_DEFINITION_WEAKUNDEF:
+    outs() << "extern-weak ";
+    break;
+  }
+  unsigned Scope = Attrs & LTO_SYMBOL_SCOPE_MASK;
+  switch (Scope) {
+  case LTO_SYMBOL_SCOPE_INTERNAL:
+    outs() << "internal ";
+    break;
+  case LTO_SYMBOL_SCOPE_HIDDEN:
+    outs() << "hidden ";
+    break;
+  case LTO_SYMBOL_SCOPE_PROTECTED:
+    outs() << "protected ";
+    break;
+  case LTO_SYMBOL_SCOPE_DEFAULT:
+    outs() << "default ";
+    break;
+  case LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN:
+    outs() << "omitted ";
+    break;
+  }
+  if (Attrs & LTO_SYMBOL_COMDAT)
+    outs() << "comdat ";
+  if (Attrs & LTO_SYMBOL_ALIAS)
+    outs() << "alias ";
+  outs() << "}";
+}
+
 /// Load each IR file and dump certain information based on active flags.
 ///
 /// The main point here is to provide lit-testable coverage for the LTOModule
@@ -421,8 +479,11 @@ static void testLTOModule(const TargetOptions &Options) {
     if (ListSymbolsOnly) {
       // List the symbols.
       outs() << Filename << ":\n";
-      for (int I = 0, E = Module->getSymbolCount(); I != E; ++I)
-        outs() << Module->getSymbolName(I) << "\n";
+      for (int I = 0, E = Module->getSymbolCount(); I != E; ++I) {
+        outs() << Module->getSymbolName(I) << "    ";
+        printLTOSymbolAttributes(Module->getSymbolAttributes(I));
+        outs() << "\n";
+      }
     }
     if (QueryHasCtorDtor)
       outs() << Filename