[GlobalOpts] mark linkonce_odr unnamed_addr GV as hidden

[steven_wu]

Summary

For the symbols are has linkonce_odr and unnamed_addr, it is safe to be
dropped from symbol table. Mark them as hidden visibility so they are
not exposed the runtime linker as weak externals.

lib/Transforms/IPO/GlobalOpt.cpp

 #include <vector>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "globalopt"
 
 STATISTIC(NumMarked    , "Number of globals marked constant");
 STATISTIC(NumUnnamed   , "Number of globals marked unnamed_addr");
+STATISTIC(NumHidden    , "Number of globals marked hidden visibility");
 STATISTIC(NumSRA       , "Number of aggregate globals broken into scalars");
 STATISTIC(NumHeapSRA   , "Number of heap objects SRA'd");
 STATISTIC(NumSubstitute,"Number of globals with initializers stored into them");
 STATISTIC(NumDeleted   , "Number of globals deleted");
 STATISTIC(NumGlobUses  , "Number of global uses devirtualized");
 STATISTIC(NumLocalized , "Number of globals localized");
 STATISTIC(NumShrunkToBool  , "Number of global vars shrunk to booleans");
 STATISTIC(NumFastCallFns   , "Number of functions converted to fastcc");
auto NewUnnamedAddr = GV.hasLocalLinkage() ? GlobalValue::UnnamedAddr::Global
                                                : GlobalValue::UnnamedAddr::Local;
     if (NewUnnamedAddr != GV.getUnnamedAddr()) {
       GV.setUnnamedAddr(NewUnnamedAddr);
       NumUnnamed++;
       Changed = true;
     }
   }
 
+  // For the linkonce_odr that marked with global unnamed addr, they are safe
+  // to be hidden.
+  if (GV.hasGlobalUnnamedAddr() && GV.hasLinkOnceODRLinkage() &&
+      !GV.hasHiddenVisibility()) {
+    GV.setVisibility(GlobalValue::HiddenVisibility);
+    NumHidden++;
+    Changed = true;
+  }
+
   // Do more involved optimizations if the global is internal.
   if (!GV.hasLocalLinkage())
     return Changed;
 
   auto *GVar = dyn_cast<GlobalVariable>(&GV);
   if (!GVar)
     return Changed;
 

test/Transforms/GlobalOpt/unnamed-addr.ll

 ; RUN: opt -globalopt -S < %s | FileCheck %s
 
 @a = internal global i32 0, align 4
 @b = internal global i32 0, align 4
 @c = internal global i32 0, align 4
 @d = internal constant [4 x i8] c"foo\00", align 1
 @e = linkonce_odr global i32 0
+@f = linkonce_odr unnamed_addr global i32 0
 
 ; CHECK: @a = internal global i32 0, align 4
 ; CHECK: @b = internal global i32 0, align 4
 ; CHECK: @c = internal unnamed_addr global i32 0, align 4
 ; CHECK: @d = internal unnamed_addr constant [4 x i8] c"foo\00", align 1
 ; CHECK: @e = linkonce_odr local_unnamed_addr global i32 0
+; CHECK: @f = linkonce_odr hidden unnamed_addr global i32 0
 
 ; CHECK: define internal fastcc void @used_internal() unnamed_addr {
 define internal void @used_internal() {
   ret void
 }
 
 define i32 @get_e() {
        call void @used_internal()
entry:
   ret i1 %cmp
 }
 
 define void @baz(i32 %x) {
 entry:
   store i32 %x, i32* @a, align 4
   store i32 %x, i32* @b, align 4
   store i32 %x, i32* @c, align 4
+  store i32 %x, i32* @f, align 4
   ret void
 }
 
 define i32 @foo(i32* %x) nounwind readnone optsize ssp {
 entry:
   %cmp = icmp eq i32* %x, @a
   %conv = zext i1 %cmp to i32
   ret i32 %conv