[PATCH] D95943: [ThinLTO] Fix import of multiply defined global variables

[Kristina Bessonova via Phabricator via llvm-commits]

krisb updated this revision to Diff 323971.
krisb marked 6 inline comments as done.
krisb retitled this revision from "[ThinLTO] Fix import of a global variable to modules contain its weak def" to "[ThinLTO] Fix import of multiply defined global variables".
krisb added a comment.

Applied review comments, reduced the test.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D95943/new/

https://reviews.llvm.org/D95943

Files:
  llvm/lib/Transforms/IPO/FunctionImport.cpp
  llvm/test/ThinLTO/X86/weak_globals_import.ll


Index: llvm/test/ThinLTO/X86/weak_globals_import.ll
===================================================================
--- /dev/null
+++ llvm/test/ThinLTO/X86/weak_globals_import.ll
@@ -0,0 +1,33 @@
+; RUN: split-file %s %t.dir
+
+; RUN: opt -module-summary %t.dir/1.ll -o %t1.bc
+; RUN: opt -module-summary %t.dir/2.ll -o %t2.bc
+
+; RUN: llvm-lto2 run -save-temps %t1.bc %t2.bc -o %t.out \
+; RUN:               -r=%t1.bc,main,plx \
+; RUN:               -r=%t1.bc,G \
+; RUN:               -r=%t2.bc,G,pl
+; RUN: llvm-dis %t.out.1.3.import.bc -o -  | FileCheck %s
+; RUN: llvm-dis %t.out.2.3.import.bc -o -  | FileCheck %s
+
+; Test that a non-prevailing def with interposable linkage doesn't prevent
+; importing a suitable definition from a prevailing module.
+
+; CHECK: @G = internal local_unnamed_addr global i32 42
+
+;--- 1.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at G = weak dso_local local_unnamed_addr global i32 0, align 4
+
+define dso_local i32 @main() local_unnamed_addr {
+  %1 = load i32, i32* @G, align 4
+  ret i32 %1
+}
+
+;--- 2.ll
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+ at G = dso_local local_unnamed_addr global i32 42, align 4
Index: llvm/lib/Transforms/IPO/FunctionImport.cpp
===================================================================
--- llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -275,6 +275,29 @@
   return Index.getValueInfo(GUID);
 }
 
+static bool shouldImportGlobal(const ValueInfo &VI,
+                               const GVSummaryMapTy &DefinedGVSummaries) {
+  const auto &GVS = DefinedGVSummaries.find(VI.getGUID());
+  if (GVS == DefinedGVSummaries.end())
+    return true;
+  // We should not skip import if the module contains a definition with
+  // interposable linkage type. This is required for correctness in
+  // the situation with two following conditions:
+  // * the def with interposable linkage is non-prevailing,
+  // * there is a prevailing def available for import and marked read-only.
+  // In this case, the non-prevailing def will be converted to a declaration,
+  // while the prevailing one becomes internal, thus no definitions will be
+  // available for linking. In order to prevent undefined symbol link error,
+  // the prevailing definition must be imported.
+  // FIXME: Consider adding a check that the suitable prevailing definition
+  // exists and marked read-only.
+  if (VI.getSummaryList().size() > 1 &&
+      GlobalValue::isInterposableLinkage(GVS->second->linkage()))
+    return true;
+
+  return false;
+}
+
 static void computeImportForReferencedGlobals(
     const GlobalValueSummary &Summary, const ModuleSummaryIndex &Index,
     const GVSummaryMapTy &DefinedGVSummaries,
@@ -282,7 +305,7 @@
     FunctionImporter::ImportMapTy &ImportList,
     StringMap<FunctionImporter::ExportSetTy> *ExportLists) {
   for (auto &VI : Summary.refs()) {
-    if (DefinedGVSummaries.count(VI.getGUID())) {
+    if (!shouldImportGlobal(VI, DefinedGVSummaries)) {
       LLVM_DEBUG(
           dbgs() << "Ref ignored! Target already in destination module.\n");
       continue;
@@ -378,6 +401,9 @@
       continue;
 
     if (DefinedGVSummaries.count(VI.getGUID())) {
+      // FIXME: Consider not skipping import if the module contains
+      // a non-prevailing def with interposable linkage. The prevailing copy
+      // can safely be imported (see shouldImportGlobal()).
       LLVM_DEBUG(dbgs() << "ignored! Target already in destination module.\n");
       continue;
     }


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