[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 86568.
pcc added a comment.

- Simplify


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 +1,22 @@
+; 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, -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=SINGLE %s
+
+; RUN: llvm-lto2 -o %t3 %t1 %t2 -r %t1,f, -r %t2,f,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=BOTH %s
+
+; RUN: llvm-lto2 -o %t3 %t2 %t1 -r %t1,f, -r %t2,f,p -save-temps
+; RUN: llvm-dis < %t3.0.0.preopt.bc -o - | FileCheck --check-prefix=BOTH %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; SINGLE: define available_externally i32 @f()
+; SINGLE-NEXT: ret i32 1
+; BOTH: define weak_odr i32 @f()
+; BOTH-NEXT: ret i32 2
+define linkonce_odr i32 @f() {
+  ret i32 1
+}
Index: llvm/test/LTO/Resolution/X86/Inputs/link-availextern.ll
===================================================================
--- /dev/null
+++ llvm/test/LTO/Resolution/X86/Inputs/link-availextern.ll
@@ -0,0 +1,6 @@
+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
+}
Index: llvm/lib/LTO/LTO.cpp
===================================================================
--- llvm/lib/LTO/LTO.cpp
+++ llvm/lib/LTO/LTO.cpp
@@ -455,20 +455,36 @@
     SymbolResolution Res = *ResI++;
     addSymbolToGlobalRes(Used, Sym, Res, 0);
 
-    if (Sym.getFlags() & object::BasicSymbolRef::SF_Undefined)
-      continue;
-    if (Res.Prevailing && Sym.isGV()) {
+    if (Sym.isGV()) {
       GlobalValue *GV = Sym.getGV();
-      Keep.push_back(GV);
-      switch (GV->getLinkage()) {
-      default:
-        break;
-      case GlobalValue::LinkOnceAnyLinkage:
-        GV->setLinkage(GlobalValue::WeakAnyLinkage);
-        break;
-      case GlobalValue::LinkOnceODRLinkage:
-        GV->setLinkage(GlobalValue::WeakODRLinkage);
-        break;
+      if (Res.Prevailing) {
+        if (Sym.getFlags() & object::BasicSymbolRef::SF_Undefined)
+          continue;
+        Keep.push_back(GV);
+        switch (GV->getLinkage()) {
+        default:
+          break;
+        case GlobalValue::LinkOnceAnyLinkage:
+          GV->setLinkage(GlobalValue::WeakAnyLinkage);
+          break;
+        case GlobalValue::LinkOnceODRLinkage:
+          GV->setLinkage(GlobalValue::WeakODRLinkage);
+          break;
+        }
+      } else if (isa<GlobalObject>(GV) &&
+                 (GV->hasLinkOnceODRLinkage() || GV->hasWeakODRLinkage() ||
+                  GV->hasAvailableExternallyLinkage())) {
+        // 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()) {
+          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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