LTO: Check local linkage first

Since visibility is meaningless for symbols with local linkage, check
local linkage before visibility when setting symbol attributes.

When linkage is `internal` and the visibility is `hidden`, the exposed
attribute is now `LTO_SYMBOL_SCOPE_INTERNAL` instead of
`LTO_SYMBOL_SCOPE_HIDDEN`.  Although the bitfield allows *both* to be
specified, the combination is nonsense anyway.

Given changes (in progress) to drop visibility when a symbol has local
linkage, this almost has no functionality change: it's mostly a cleanup
to clarify the logic.

The exception is when something has `appending` linkage.  Before this
change, such symbols would be advertised as `LTO_SYMBOL_SCOPE_INTERNAL`;
now, they'll be given `LTO_SYMBOL_SCOPE_COMMON`.

Unfortunately this is really awkward to test.  This only changes what we
advertise to linkers (before running LTO), not what the final object
looks like.  In theory I could add `DEBUG` output to `llvm-lto` (and
test with "REQUIRES: asserts"), but follow-up commits to disallow
`internal hidden` simplify this anyway.

<rdar://problem/16141113>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208261 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/LTO/LTOModule.cpp b/lib/LTO/LTOModule.cpp
index b687f29c6598ae161687ce3a3548c587e8b14a42..93730ddb4510a1fa272c7377ea909925697b6b01 100644 (file)
--- a/lib/LTO/LTOModule.cpp
+++ b/lib/LTO/LTOModule.cpp
@@ -418,17 +418,17 @@ void LTOModule::addDefinedSymbol(const GlobalValue *def, bool isFunction) {
     attr |= LTO_SYMBOL_DEFINITION_REGULAR;
 
   // set scope part
-  if (def->hasHiddenVisibility())
+  if (def->hasLocalLinkage())
+    // Ignore visibility if linkage is local.
+    attr |= LTO_SYMBOL_SCOPE_INTERNAL;
+  else if (def->hasHiddenVisibility())
     attr |= LTO_SYMBOL_SCOPE_HIDDEN;
   else if (def->hasProtectedVisibility())
     attr |= LTO_SYMBOL_SCOPE_PROTECTED;
   else if (canBeHidden(def))
     attr |= LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN;
-  else if (def->hasExternalLinkage() || def->hasWeakLinkage() ||
-           def->hasLinkOnceLinkage() || def->hasCommonLinkage())
-    attr |= LTO_SYMBOL_SCOPE_DEFAULT;
   else
-    attr |= LTO_SYMBOL_SCOPE_INTERNAL;
+    attr |= LTO_SYMBOL_SCOPE_DEFAULT;
 
   StringSet::value_type &entry = _defines.GetOrCreateValue(Buffer);
   entry.setValue(1);