[ThinLTO] - Stop internalizing and drop non-prevailing symbols.

Implementation marks non-prevailing symbols as not live in the summary.
Then them are dropped in backends.

Fixes https://bugs.llvm.org/show_bug.cgi?id=35938

Differential revision: https://reviews.llvm.org/D42107

llvm-svn: 323633

1 files changed, 30 insertions, 20 deletions

diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index ed85c20051e..8dbee83bc3e 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -163,6 +163,9 @@ selectCallee(const ModuleSummaryIndex &Index,
       CalleeSummaryList,
       [&](const std::unique_ptr<GlobalValueSummary> &SummaryPtr) {
         auto *GVSummary = SummaryPtr.get();
+        if (!Index.isGlobalValueLive(GVSummary))
+          return false;
+
         // For SamplePGO, in computeImportForFunction the OriginalId
         // may have been used to locate the callee summary list (See
         // comment there).
@@ -495,7 +498,8 @@ void llvm::ComputeCrossModuleImportForModuleFromIndex(
 
 void llvm::computeDeadSymbols(
     ModuleSummaryIndex &Index,
-    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
+    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols,
+    function_ref<PrevailingType(GlobalValue::GUID)> isPrevailing) {
   assert(!Index.withGlobalValueDeadStripping());
   if (!ComputeDead)
     return;
@@ -524,7 +528,6 @@ void llvm::computeDeadSymbols(
       }
 
   // Make value live and add it to the worklist if it was not live before.
-  // FIXME: we should only make the prevailing copy live here
   auto visit = [&](ValueInfo VI) {
     // FIXME: If we knew which edges were created for indirect call profiles,
     // we could skip them here. Any that are live should be reached via
@@ -540,6 +543,11 @@ void llvm::computeDeadSymbols(
     for (auto &S : VI.getSummaryList())
       if (S->isLive())
         return;
+
+    // We do not keep live symbols that are known to be non-prevailing.
+    if (isPrevailing(VI.getGUID()) == PrevailingType::No)
+      return;
+
     for (auto &S : VI.getSummaryList())
       S->setLive(true);
     ++LiveSymbols;
@@ -550,6 +558,8 @@ void llvm::computeDeadSymbols(
     auto VI = Worklist.pop_back_val();
     for (auto &Summary : VI.getSummaryList()) {
       GlobalValueSummary *Base = Summary->getBaseObject();
+      // Set base value live in case it is an alias.
+      Base->setLive(true);
       for (auto Ref : Base->refs())
         visit(Ref);
       if (auto *FS = dyn_cast<FunctionSummary>(Base))
@@ -603,26 +613,26 @@ llvm::EmitImportsFiles(StringRef ModulePath, StringRef OutputFilename,
   return std::error_code();
 }
 
+void llvm::convertToDeclaration(GlobalValue &GV) {
+  DEBUG(dbgs() << "Converting to a declaration: `" << GV.getName() << "\n");
+  if (Function *F = dyn_cast<Function>(&GV)) {
+    F->deleteBody();
+    F->clearMetadata();
+  } else if (GlobalVariable *V = dyn_cast<GlobalVariable>(&GV)) {
+    V->setInitializer(nullptr);
+    V->setLinkage(GlobalValue::ExternalLinkage);
+    V->clearMetadata();
+  } else
+    // For now we don't resolve or drop aliases. Once we do we'll
+    // need to add support here for creating either a function or
+    // variable declaration, and return the new GlobalValue* for
+    // the caller to use.
+    llvm_unreachable("Expected function or variable");
+}
+
 /// Fixup WeakForLinker linkages in \p TheModule based on summary analysis.
 void llvm::thinLTOResolveWeakForLinkerModule(
     Module &TheModule, const GVSummaryMapTy &DefinedGlobals) {
-  auto ConvertToDeclaration = [](GlobalValue &GV) {
-    DEBUG(dbgs() << "Converting to a declaration: `" << GV.getName() << "\n");
-    if (Function *F = dyn_cast<Function>(&GV)) {
-      F->deleteBody();
-      F->clearMetadata();
-    } else if (GlobalVariable *V = dyn_cast<GlobalVariable>(&GV)) {
-      V->setInitializer(nullptr);
-      V->setLinkage(GlobalValue::ExternalLinkage);
-      V->clearMetadata();
-    } else
-      // For now we don't resolve or drop aliases. Once we do we'll
-      // need to add support here for creating either a function or
-      // variable declaration, and return the new GlobalValue* for
-      // the caller to use.
-      llvm_unreachable("Expected function or variable");
-  };
-
   auto updateLinkage = [&](GlobalValue &GV) {
     // See if the global summary analysis computed a new resolved linkage.
     const auto &GS = DefinedGlobals.find(GV.getGUID());
@@ -653,7 +663,7 @@ void llvm::thinLTOResolveWeakForLinkerModule(
     // the definition in that case.
     if (GlobalValue::isAvailableExternallyLinkage(NewLinkage) &&
         GlobalValue::isInterposableLinkage(GV.getLinkage()))
-      ConvertToDeclaration(GV);
+      convertToDeclaration(GV);
     else {
       DEBUG(dbgs() << "ODR fixing up linkage for `" << GV.getName() << "` from "
                    << GV.getLinkage() << " to " << NewLinkage << "\n");