Symbols re-defined with -wrap and -defsym need to be excluded from inter-

procedural optimizations to prevent dropping symbols and allow the linker
to process re-directs.

PR33145: --wrap doesn't work with lto.
Differential Revision: https://reviews.llvm.org/D33621

llvm-svn: 304719

include/llvm/LTO/LTO.h

@@ -366,8 +366,9 @@ private:
 /// each global symbol based on its internal resolution of that symbol.
 struct SymbolResolution {
   SymbolResolution()
-      : Prevailing(0), FinalDefinitionInLinkageUnit(0), VisibleToRegularObj(0) {
-  }
+      : Prevailing(0), FinalDefinitionInLinkageUnit(0), VisibleToRegularObj(0),
+        LinkerRedefined(0) {}
+
   /// The linker has chosen this definition of the symbol.
   unsigned Prevailing : 1;
 
@@ -377,6 +378,10 @@ struct SymbolResolution {
 
   /// The definition of this symbol is visible outside of the LTO unit.
   unsigned VisibleToRegularObj : 1;
+
+  /// Linker redefined version of the symbol which appeared in -wrap or -defsym
+  /// linker option.
+  unsigned LinkerRedefined : 1;
 };
 
 } // namespace lto

lib/LTO/LTO.cpp

@@ -405,10 +405,11 @@ void LTO::addSymbolToGlobalRes(const InputFile::Symbol &Sym,
   if (Res.Prevailing)
     GlobalRes.IRName = Sym.getIRName();
 
-  // Set the partition to external if we know it is used elsewhere, e.g.
-  // it is visible to a regular object, is referenced from llvm.compiler_used,
-  // or was already recorded as being referenced from a different partition.
-  if (Res.VisibleToRegularObj || Sym.isUsed() ||
+  // Set the partition to external if we know it is re-defined by the linker
+  // with -defsym or -wrap options, used elsewhere, e.g. it is visible to a
+  // regular object, is referenced from llvm.compiler_used, or was already
+  // recorded as being referenced from a different partition.
+  if (Res.LinkerRedefined || Res.VisibleToRegularObj || Sym.isUsed() ||
       (GlobalRes.Partition != GlobalResolution::Unknown &&
        GlobalRes.Partition != Partition)) {
     GlobalRes.Partition = GlobalResolution::External;
@@ -439,6 +440,8 @@ static void writeToResolutionFile(raw_ostream &OS, InputFile *Input,
       OS << 'l';
     if (Res.VisibleToRegularObj)
       OS << 'x';
+    if (Res.LinkerRedefined)
+      OS << 'r';
     OS << '\n';
   }
   OS.flush();
@@ -543,6 +546,12 @@ Error LTO::addRegularLTO(BitcodeModule BM,
         if (Sym.isUndefined())
           continue;
         Keep.push_back(GV);
+        // For symbols re-defined with linker -wrap and -defsym options,
+        // set the linkage to weak to inhibit IPO. The linkage will be
+        // restored by the linker.
+        if (Res.LinkerRedefined)
+          GV->setLinkage(GlobalValue::WeakAnyLinkage);
+
         GlobalValue::LinkageTypes OriginalLinkage = GV->getLinkage();
         if (GlobalValue::isLinkOnceLinkage(OriginalLinkage))
           GV->setLinkage(GlobalValue::getWeakLinkage(

test/LTO/Resolution/X86/linker-redef.ll

@@ -0,0 +1,16 @@
+; RUN: llvm-as %s -o %t.o
+; RUN: llvm-lto2 run -o %t1.o %t.o -r %t.o,bar,pr
+; RUN: llvm-readobj -t %t1.o.0 | FileCheck %s
+
+; CHECK: Name: bar
+; CHECK-NEXT: Value:
+; CHECK-NEXT: Size:
+; CHECK-NEXT: Binding: Weak
+; CHECK-NEXT: Type: Function
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @bar() {
+  ret void
+}

tools/llvm-lto2/llvm-lto2.cpp

@@ -162,6 +162,8 @@ static int run(int argc, char **argv) {
         Res.FinalDefinitionInLinkageUnit = true;
       else if (C == 'x')
         Res.VisibleToRegularObj = true;
+      else if (C == 'r')
+        Res.LinkerRedefined = true;
       else {
         llvm::errs() << "invalid character " << C << " in resolution: " << R
                      << '\n';