ThinLTO: do not import function whose linkage prevents inlining.

There is not point in importing a "weak" or a "linkonce" function
since we won't be able to inline it anyway.
We already had a targeted check for WeakAny, this is using the
same check on GlobalValue as the inline, i.e.
isMayBeOverriddenLinkage()

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 268315

llvm/include/llvm/IR/GlobalValue.h

@@ -124,26 +124,7 @@ private:
   /// non-equivalent at link time. For example, if a function has weak linkage
   /// then the code defining it may be replaced by different code.
   bool mayBeOverridden() const {
-    switch (getLinkage()) {
-    case WeakAnyLinkage:
-    case LinkOnceAnyLinkage:
-    case CommonLinkage:
-    case ExternalWeakLinkage:
-      return true;
-
-    case AvailableExternallyLinkage:
-    case LinkOnceODRLinkage:
-    case WeakODRLinkage:
-      // The above three cannot be overridden but can be de-refined.
-
-    case ExternalLinkage:
-    case AppendingLinkage:
-    case InternalLinkage:
-    case PrivateLinkage:
-      return false;
-    }
-
-    llvm_unreachable("Fully covered switch above!");
+    return isMayBeOverriddenLinkage(getLinkage());
   }
 
 protected:
@@ -285,6 +266,31 @@ public:
     return Linkage == CommonLinkage;
   }
 
+  /// Whether the definition of this global may be replaced by something
+  /// non-equivalent at link time. For example, if a function has weak linkage
+  /// then the code defining it may be replaced by different code.
+  static bool isMayBeOverriddenLinkage(LinkageTypes Linkage) {
+    switch (Linkage) {
+    case WeakAnyLinkage:
+    case LinkOnceAnyLinkage:
+    case CommonLinkage:
+    case ExternalWeakLinkage:
+      return true;
+
+    case AvailableExternallyLinkage:
+    case LinkOnceODRLinkage:
+    case WeakODRLinkage:
+    // The above three cannot be overridden but can be de-refined.
+
+    case ExternalLinkage:
+    case AppendingLinkage:
+    case InternalLinkage:
+    case PrivateLinkage:
+      return false;
+    }
+    llvm_unreachable("Fully covered switch above!");
+  }
+
   /// Whether the definition of this global may be discarded if it is not used
   /// in its compilation unit.
   static bool isDiscardableIfUnused(LinkageTypes Linkage) {

llvm/lib/Transforms/IPO/FunctionImport.cpp

@@ -156,8 +156,8 @@ selectCallee(const ModuleSummaryIndex &Index,
       CalleeSummaryList,
       [&](const std::unique_ptr<GlobalValueSummary> &SummaryPtr) {
         auto *GVSummary = SummaryPtr.get();
-        if (GlobalValue::isWeakAnyLinkage(GVSummary->linkage()))
-          // There is no point in importing weak symbols, we can't inline them
+        if (GlobalValue::isMayBeOverriddenLinkage(GVSummary->linkage()))
+          // There is no point in importing these, we can't inline them
           return false;
         if (auto *AS = dyn_cast<AliasSummary>(GVSummary)) {
           GVSummary = &AS->getAliasee();

llvm/test/Transforms/FunctionImport/Inputs/funcimport.ll

@@ -75,6 +75,11 @@ entry:
   ret void
 }
 
+define linkonce void @linkoncefunc2() #0 {
+entry:
+  ret void
+}
+
 define internal i32 @staticfunc() #0 {
 entry:
   ret i32 1

llvm/test/Transforms/FunctionImport/funcimport.ll

@@ -28,6 +28,7 @@ entry:
   call void (...) @setfuncptr()
   call void (...) @callfuncptr()
   call void (...) @weakfunc()
+  call void (...) @linkoncefunc2()
   call void (...) @referencelargelinkonce()
   ret i32 0
 }
@@ -94,6 +95,10 @@ declare void @referencelargelinkonce(...)
 ; CHECK-DAG: declare void @weakfunc(...)
 declare void @weakfunc(...) #1
 
+; Won't import linkonce func
+; CHECK-DAG: declare void @linkoncefunc2(...)
+declare void @linkoncefunc2(...) #1
+
 ; INSTLIMDEF-DAG: Import funcwithpersonality
 ; INSTLIMDEF-DAG: define available_externally hidden void @funcwithpersonality.llvm.{{.*}}() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
 ; INSTLIM5-DAG: declare hidden void @funcwithpersonality.llvm.{{.*}}()