[LTO] Fix the interaction between linker redefined symbols and ThinLTO

This is the same as r304719 but for ThinLTO.
The substantial difference is that in this case we don't have
whole visibility, just the summary.
In the LTO case, when we got the resolution for the input file we
could just see if the linker told us whether a symbol was linker
redefined (using --wrap or --defsym) and switch the linkage directly
for the GV.

Here, we have the summary. So, we record that the linkage changed
from <whatever it was> to $weakany to prevent IPOs across this symbol
boundaries and actually just switch the linkage at FunctionImport time.

This patch should also fixes the lld bits (as all the scaffolding for
communicating if a symbol is linker redefined should be there & should
be the same), but I'll make sure to add some tests there as well.

Fixes PR33192.

Differential Revision:  https://reviews.llvm.org/D35064

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307303 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/LTO/LTO.cpp b/lib/LTO/LTO.cpp
index 68b8c9fcb939f324657dcbaab2678f6de7999901..8be5312b9208d8c7d57223a4b8fb56b08e533589 100644 (file)
--- a/lib/LTO/LTO.cpp
+++ b/lib/LTO/LTO.cpp
@@ -665,6 +665,15 @@ Error LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
         auto GUID = GlobalValue::getGUID(GlobalValue::getGlobalIdentifier(
             Sym.getIRName(), GlobalValue::ExternalLinkage, ""));
         ThinLTO.PrevailingModuleForGUID[GUID] = BM.getModuleIdentifier();
+
+        // For linker redefined symbols (via --wrap or --defsym) we want to
+        // switch the linkage to `weak` to prevent IPOs from happening.
+        // Find the summary in the module for this very GV and record the new
+        // linkage so that we can switch it when we import the GV.
+        if (Res.LinkerRedefined)
+          if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(
+                  GUID, BM.getModuleIdentifier()))
+            S->setLinkage(GlobalValue::WeakAnyLinkage);
       }
     }
   }

diff --git a/lib/Transforms/IPO/FunctionImport.cpp b/lib/Transforms/IPO/FunctionImport.cpp
index 6d34ab8b0d9608153ae43c54c48ea344096824fc..5e7cf436e2e3fabc8e4446737bce369899f56f6d 100644 (file)
--- a/lib/Transforms/IPO/FunctionImport.cpp
+++ b/lib/Transforms/IPO/FunctionImport.cpp
@@ -537,8 +537,6 @@ void llvm::thinLTOResolveWeakForLinkerModule(
   };
 
   auto updateLinkage = [&](GlobalValue &GV) {
-    if (!GlobalValue::isWeakForLinker(GV.getLinkage()))
-      return;
     // See if the global summary analysis computed a new resolved linkage.
     const auto &GS = DefinedGlobals.find(GV.getGUID());
     if (GS == DefinedGlobals.end())
@@ -546,6 +544,16 @@ void llvm::thinLTOResolveWeakForLinkerModule(
     auto NewLinkage = GS->second->linkage();
     if (NewLinkage == GV.getLinkage())
       return;
+
+    // Switch the linkage to weakany if asked for, e.g. we do this for
+    // linker redefined symbols (via --wrap or --defsym).
+    if (NewLinkage == GlobalValue::WeakAnyLinkage) {
+      GV.setLinkage(NewLinkage);
+      return;
+    }
+
+    if (!GlobalValue::isWeakForLinker(GV.getLinkage()))
+      return;
     // Check for a non-prevailing def that has interposable linkage
     // (e.g. non-odr weak or linkonce). In that case we can't simply
     // convert to available_externally, since it would lose the

diff --git a/test/LTO/Resolution/X86/linker-redef-thin.ll b/test/LTO/Resolution/X86/linker-redef-thin.ll
new file mode 100644 (file)
index 0000000..ebaac80
--- /dev/null
+++ b/test/LTO/Resolution/X86/linker-redef-thin.ll
@@ -0,0 +1,16 @@
+; RUN: opt -module-summary %s -o %t.o
+; RUN: llvm-lto2 run -o %t1.o %t.o -r %t.o,patatino,pr
+; RUN: llvm-readobj -t %t1.o.0 | FileCheck %s
+
+; CHECK: Name: patatino
+; 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 @patatino() {
+  ret void
+}