[PATCH] D29367: LTO: Link non-prevailing weak_odr, linkonce_odr or available_externally globals into the combined module with available_externally linkage.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc updated this revision to Diff 86754.
pcc added a dependency: D29435: Linker: Move special casing for available_externally in IRMover to clients. NFCI..
pcc added a comment.

Depends on https://reviews.llvm.org/D29435


https://reviews.llvm.org/D29367

Files:
  llvm/lib/LTO/LTO.cpp
  llvm/test/LTO/Resolution/X86/Inputs/link-availextern.ll
  llvm/test/LTO/Resolution/X86/link-availextern.ll


Index: llvm/test/LTO/Resolution/X86/link-availextern.ll
===================================================================
--- /dev/null
+++ llvm/test/LTO/Resolution/X86/link-availextern.ll
@@ -0,0 +1,30 @@
+; RUN: llvm-as %s -o %t1
+; RUN: llvm-as %S/Inputs/link-availextern.ll -o %t2
+
+; RUN: llvm-lto2 -o %t3 %t1 -r %t1,f, -r %t1,f2,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=NONPREVAILING %s
+
+; RUN: llvm-lto2 -o %t3 %t1 %t2 -r %t1,f, -r %t1,f2,p -r %t2,f, -r %t2,f3,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=NONPREVAILING %s
+
+; RUN: llvm-lto2 -o %t3 %t1 %t2 -r %t1,f, -r %t1,f2,p -r %t2,f,p -r %t2,f3,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=PREVAILING %s
+
+; RUN: llvm-lto2 -o %t3 %t2 %t1 -r %t1,f, -r %t1,f2,p -r %t2,f,p -r %t2,f3,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=PREVAILING %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; NONPREVAILING: define available_externally i32 @f()
+; NONPREVAILING-NEXT: ret i32 1
+; PREVAILING: define weak_odr i32 @f()
+; PREVAILING-NEXT: ret i32 2
+define linkonce_odr i32 @f() {
+  ret i32 1
+}
+
+define void @f2() {
+  %x = call i32 @f()
+  ret void
+}
Index: llvm/test/LTO/Resolution/X86/Inputs/link-availextern.ll
===================================================================
--- /dev/null
+++ llvm/test/LTO/Resolution/X86/Inputs/link-availextern.ll
@@ -0,0 +1,11 @@
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define linkonce_odr i32 @f() {
+  ret i32 2
+}
+
+define void @f3() {
+  %x = call i32 @f()
+  ret void
+}
Index: llvm/lib/LTO/LTO.cpp
===================================================================
--- llvm/lib/LTO/LTO.cpp
+++ llvm/lib/LTO/LTO.cpp
@@ -446,6 +446,11 @@
     if (GV.hasAppendingLinkage())
       Keep.push_back(&GV);
 
+  DenseSet<GlobalObject *> AliasedGlobals;
+  for (auto &GA : M.aliases())
+    if (GlobalObject *GO = GA.getBaseObject())
+      AliasedGlobals.insert(GO);
+
   for (const InputFile::Symbol &Sym :
        make_range(InputFile::symbol_iterator(SymTab.symbols().begin(), SymTab,
                                              nullptr),
@@ -471,13 +476,21 @@
           GV->setLinkage(GlobalValue::WeakODRLinkage);
           break;
         }
-      } else if (GV->hasAvailableExternallyLinkage()) {
-        // We can link available_externally symbols even if they are
-        // non-prevailing.
+      } else if (isa<GlobalObject>(GV) &&
+                 (GV->hasLinkOnceODRLinkage() || GV->hasWeakODRLinkage() ||
+                  GV->hasAvailableExternallyLinkage()) &&
+                 !AliasedGlobals.count(cast<GlobalObject>(GV))) {
+        // Either of the above three types of linkage indicates that the
+        // chosen prevailing symbol will have the same semantics as this copy of
+        // the symbol, so we can link it with available_externally linkage. We
+        // only need to do this if the symbol is undefined.
         GlobalValue *CombinedGV =
             RegularLTO.CombinedModule->getNamedValue(GV->getName());
-        if (!CombinedGV || CombinedGV->isDeclaration())
+        if (!CombinedGV || CombinedGV->isDeclaration()) {
           Keep.push_back(GV);
+          GV->setLinkage(GlobalValue::AvailableExternallyLinkage);
+          cast<GlobalObject>(GV)->setComdat(nullptr);
+        }
       }
     }
     // Common resolution: collect the maximum size/alignment over all commons.


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