[ThinLTO] Auto-hide prevailing linkonce_odr only when all copies eligible

[tejohnson]

Summary

We hit undefined references building with ThinLTO when one source file
contained explicit instantiations of a template method (weak_odr) but
there were also implicit instantiations in another file (linkonce_odr),
and the latter was the prevailing copy. In this case the symbol was
marked hidden when the prevailing linkonce_odr copy was promoted to
weak_odr. It led to unsats when the resulting shared library was linked
with other code that contained a reference (expecting to be resolved due
to the explicit instantiation).

Add a CanAutoHide flag to the GV summary to allow the thin link to
identify when all copies are eligible for auto-hiding (because they were
all originally linkonce_odr global unnamed addr), and only do the
auto-hide in that case.

Most of the changes here are due to plumbing the new flag through the
bitcode and llvm assembly, and resulting test changes. I augmented the
existing auto-hide test to check for this situation.

[steven_wu]

I am not quite sure what is the semantics for ELF linker. When thinLTO picks the linkonce_odr version and promote it to weak, it is not changing the visibility. It is a later linker optimization that auto hide the linkonce_odr symbol, correct?

If that is the case, would it be a problem for non-LTO link as well? ld64 always prefers the symbol that is not autohide so I don't think it will run into this situation.

[tejohnson]

In D59709#1440017, @steven_wu wrote:

I am not quite sure what is the semantics for ELF linker. When thinLTO picks the linkonce_odr version and promote it to weak, it is not changing the visibility. It is a later linker optimization that auto hide the linkonce_odr symbol, correct?

It is in fact ThinLTO that is changing the visibility (D43130). See the change I made to FunctionImport.cpp.

If that is the case, would it be a problem for non-LTO link as well? ld64 always prefers the symbol that is not autohide so I don't think it will run into this situation.

pcc@ looked at this and found that ELF semantics picks the most hidden visibility. However, without ThinLTO we aren't marking any of these as hidden, so it isn't an issue.

[steven_wu]

In D59709#1440033, @tejohnson wrote:

In D59709#1440017, @steven_wu wrote:

I am not quite sure what is the semantics for ELF linker. When thinLTO picks the linkonce_odr version and promote it to weak, it is not changing the visibility. It is a later linker optimization that auto hide the linkonce_odr symbol, correct?

It is in fact ThinLTO that is changing the visibility (D43130). See the change I made to FunctionImport.cpp.

Interesting, I made that change! But I somehow remembered I got pushed back because of ELF semantics and end up implementing that in ld64 instead. Let me dig up some context and get back to you.

If that is the case, would it be a problem for non-LTO link as well? ld64 always prefers the symbol that is not autohide so I don't think it will run into this situation.

pcc@ looked at this and found that ELF semantics picks the most hidden visibility. However, without ThinLTO we aren't marking any of these as hidden, so it isn't an issue.

I see, so if ELF linker doesn't have this autohide optimization, it should be fine in this specific case (but I thought there are some ELF linker actually does this).

[tejohnson]

In D59709#1440081, @steven_wu wrote:

In D59709#1440033, @tejohnson wrote:

In D59709#1440017, @steven_wu wrote:

I am not quite sure what is the semantics for ELF linker. When thinLTO picks the linkonce_odr version and promote it to weak, it is not changing the visibility. It is a later linker optimization that auto hide the linkonce_odr symbol, correct?

It is in fact ThinLTO that is changing the visibility (D43130). See the change I made to FunctionImport.cpp.

Interesting, I made that change! But I somehow remembered I got pushed back because of ELF semantics and end up implementing that in ld64 instead. Let me dig up some context and get back to you.

Are you thinking of https://reviews.llvm.org/D43361?

If that is the case, would it be a problem for non-LTO link as well? ld64 always prefers the symbol that is not autohide so I don't think it will run into this situation.

pcc@ looked at this and found that ELF semantics picks the most hidden visibility. However, without ThinLTO we aren't marking any of these as hidden, so it isn't an issue.

I see, so if ELF linker doesn't have this autohide optimization, it should be fine in this specific case (but I thought there are some ELF linker actually does this).

@pcc might have some info here. But I don't think so. We just can't mark hidden without the global visibility of all symbols, as we have here with ThinLTO (because of ELF picking the most hidden one).

[steven_wu]

In D59709#1440113, @tejohnson wrote:

In D59709#1440081, @steven_wu wrote:

In D59709#1440033, @tejohnson wrote:

In D59709#1440017, @steven_wu wrote:

I am not quite sure what is the semantics for ELF linker. When thinLTO picks the linkonce_odr version and promote it to weak, it is not changing the visibility. It is a later linker optimization that auto hide the linkonce_odr symbol, correct?

It is in fact ThinLTO that is changing the visibility (D43130). See the change I made to FunctionImport.cpp.

Interesting, I made that change! But I somehow remembered I got pushed back because of ELF semantics and end up implementing that in ld64 instead. Let me dig up some context and get back to you.

Are you thinking of https://reviews.llvm.org/D43361?

That is exactly what I was thinking.

If that is the case, would it be a problem for non-LTO link as well? ld64 always prefers the symbol that is not autohide so I don't think it will run into this situation.

pcc@ looked at this and found that ELF semantics picks the most hidden visibility. However, without ThinLTO we aren't marking any of these as hidden, so it isn't an issue.

I see, so if ELF linker doesn't have this autohide optimization, it should be fine in this specific case (but I thought there are some ELF linker actually does this).

@pcc might have some info here. But I don't think so. We just can't mark hidden without the global visibility of all symbols, as we have here with ThinLTO (because of ELF picking the most hidden one).

If this is really linker semantics difference, would it be easier if just make the visibility hidden change in D43130 be target specific?

[pcc]

Does this has the correct behaviour in the case where the explicit instantiation is in a regular object file and the implicit instantiation is in bitcode?

In D59709#1440173, @steven_wu wrote:

In D59709#1440113, @tejohnson wrote:

@pcc might have some info here. But I don't think so. We just can't mark hidden without the global visibility of all symbols, as we have here with ThinLTO (because of ELF picking the most hidden one).

ELF linkers don't do auto-hide because it would require extending ELF to store the auto-hide bit (or information from which it can be recovered) somewhere. We have extended ELF with an address-significance table which tells us whether symbols are (local_)unnamed_addr, but we aren't keeping track of whether symbols are linkonce_odr.

If this is really linker semantics difference, would it be easier if just make the visibility hidden change in D43130 be target specific?

That would mean losing the auto hide optimization on ELF. I don't think we should do that.

include/llvm/IR/ModuleSummaryIndex.h

202

canAutoHide? (same elsewhere)

lib/Transforms/IPO/FunctionImport.cpp

984

Can't it also be local_unnamed_addr?

[steven_wu]

Thanks for explanation. Then the current approach in this patch LGTM. Thanks!

[tejohnson]

In D59709#1440303, @pcc wrote:

Does this has the correct behaviour in the case where the explicit instantiation is in a regular object file and the implicit instantiation is in bitcode?

Hmm, no. Nor will it work when the explicit instantiation is in a bitcode file without a summary. I can fix these cases by utilizing the VisibleOutsideSummary flag on the GlobalResolution to conservatively set CanAutoHide=false when that is set.

In D59709#1440173, @steven_wu wrote:

In D59709#1440113, @tejohnson wrote:

@pcc might have some info here. But I don't think so. We just can't mark hidden without the global visibility of all symbols, as we have here with ThinLTO (because of ELF picking the most hidden one).

ELF linkers don't do auto-hide because it would require extending ELF to store the auto-hide bit (or information from which it can be recovered) somewhere. We have extended ELF with an address-significance table which tells us whether symbols are (local_)unnamed_addr, but we aren't keeping track of whether symbols are linkonce_odr.

If this is really linker semantics difference, would it be easier if just make the visibility hidden change in D43130 be target specific?

That would mean losing the auto hide optimization on ELF. I don't think we should do that.

include/llvm/IR/ModuleSummaryIndex.h

202

Will do.

lib/Transforms/IPO/FunctionImport.cpp

984

I don't know but I wanted to maintain the status quo on that - we only did this in the global unnamed addr case before. If it can be changed to local_unnamed_addr that should probably be done as a follow up.

[tejohnson]

In D59709#1440441, @tejohnson wrote:

In D59709#1440303, @pcc wrote:

Does this has the correct behaviour in the case where the explicit instantiation is in a regular object file and the implicit instantiation is in bitcode?

Hmm, no. Nor will it work when the explicit instantiation is in a bitcode file without a summary. I can fix these cases by utilizing the VisibleOutsideSummary flag on the GlobalResolution to conservatively set CanAutoHide=false when that is set.

The GUIDPreservedSymbols set already has the set of GUIDs that are visible outside the summary, so I just made a change to pass that down and check it as well. Added a case to the test that checks for this situation (one module without summary).

[tejohnson]

Address comments

[tejohnson]

Added a gold test so that we can test the native object case too.

[tejohnson]

ping

[tejohnson]

ping

[tejohnson]

ping - @pcc any more comments or can this fix go in now?

[tejohnson]

Ping - ok if I submit this bugfix?

[pcc]

I think there might still be a problem where we're dropping the distinction between visible to other translation units and visible outside the linkage unit. This is related to the distinction between LDPR_PREVAILING_DEF_IRONLY and LDPR_PREVAILING_DEF_IRONLY_EXP in the gold plugin interface. Let me look into it a bit more and get back to you.

[pcc]

LGTM

Sorry for the long delay in reviewing this.

In D59709#1498204, @pcc wrote:

I think there might still be a problem where we're dropping the distinction between visible to other translation units and visible outside the linkage unit. This is related to the distinction between LDPR_PREVAILING_DEF_IRONLY and LDPR_PREVAILING_DEF_IRONLY_EXP in the gold plugin interface. Let me look into it a bit more and get back to you.

I don't think this is a problem. After having reminded myself about how things work, I realise that the linkers already keep track of this distinction and reflect it in the VisibleToRegularObj field.

lib/Transforms/IPO/FunctionImport.cpp

984

Okay, I missed that you were checking for global unnamed_addr when setting the flag to begin with.

[steven_wu]

Hi Teresa, I am seeing some regressions because of this commit. ThinLTO is now producing more weak symbols than before and I am looking for a good fix. See inline comments for details.

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

The regression I saw is exactly the situation mentioned in the comments but I am not so sure about the conclusion here. For ld64, it can see whether a symbol can be auto hide or not, and it prefers the one that is not auto hide. This means if there are other copies of the symbol that is not autohide outside the summary and not autohide, the one can be autohide should never be prevailing.

Is that the case for other linker?

[tejohnson]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

The regression I saw is exactly the situation mentioned in the comments but I am not so sure about the conclusion here.

By the situation mentioned in the comments I assume you mean the part about symbols in the GUIDPreservedSymbols set because they are visible outside the summary? In your situation, why are there so many symbols in the preserved symbols set? Are there a lot of symbols in native code being linked in?

I guess it is different in lld since in the case I encountered (in an internal application), the linkonce_odr copy was prevailing, not the weak_odr copy. If ld64 guarantees that the autohide (linkonce_odr) copy will never be prevailing if there is an autohide (weak_odr) copy available somewhere, then we may need to figure out a way to communicate that.

[tejohnson]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

If ld64 guarantees that the autohide (linkonce_odr) copy will never be prevailing if there is an autohide (weak_odr) copy available somewhere

I meant if there is a *non*-autohide (weak_odr) copy available of course...

[steven_wu]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

By the situation mentioned in the comments I assume you mean the part about symbols in the GUIDPreservedSymbols set because they are visible outside the summary? In your situation, why are there so many symbols in the preserved symbols set? Are there a lot of symbols in native code being linked in?

Yes. The situation is the code is linking a static c++ library (native code) with linkonce autohide libcxx symbols. Since ld64 decides to coalesce away the copy in the native code and use the version inside the LTO, it has to add it to mustPreserve symbols. Now even both copies can be autohide, it is not autohide because it is in the preserve list.

I guess it is different in lld since in the case I encountered (in an internal application), the linkonce_odr copy was prevailing, not the weak_odr copy. If ld64 guarantees that the autohide (linkonce_odr) copy will never be prevailing if there is an autohide (weak_odr) copy available somewhere, then we may need to figure out a way to communicate that.

This sounds like a linker bug but I am not familiar with lld LTO pipeline to be sure. Should lld mark weak_odr copy as prevailing? I also would like to understand how lld is using mustPreserve symbols because I thought lld doesn't need it.
For ld64, it uses mustPreserve symbol to communicate if the weak/linkonce symbols are prevailing in this case.

[tejohnson]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

In the new LTO API, symbols are added to the GUIDPreservedSymbols set if they are visible outside the summary (either in a bitcode file without a summary or a native object).

We could do better if the linker indicated whether these symbols in objects without summaries were eligible for auto hide, which in the compiler is based both on the linkage type and on it having the global unnamed addr flag - does the linker know both of these for native objects?

I'm not an lld expert, but looking back at my original internal discussion with @pcc on this issue, it appears to be a difference in ld64 (Mach-O) semantics and ELF semantics. Here is an excerpt:

pcc wrote:

tejohnson wrote:

Is there some other criteria that should be used to prevent the symbol from being marked Hidden in this case?

It seems that the rule should be: if we see at least one weak_odr definition (i.e. explicit instantiation) that should prevent the relaxation from default to hidden. The reason is that the weak_odr makes it possible to have another translation unit that does not implicitly instantiate the function, including a translation unit in another DSO. Similar logic is implemented in ld64: if one symbol is weak_odr unnamed_addr (i.e. non-auto-hide) and the other is linkonce_odr unnamed_addr (i.e. auto-hide), the linker selects the non-auto-hide one.
https://github.com/apple-opensource/ld64/blob/master/src/ld/SymbolTable.cpp#L228

Unfortunately, this is at odds with ELF semantics where the "most hidden" visibility wins, so I think this means that we would not be able to mark linkonce_odr unnamed_addr symbols as hidden in the non-LTO case, as was suggested at one point on llvm-dev I believe.

So perhaps the best thing to do in this case is have an interface for the linker to indicate the correct semantics with regard to whether most or least hidden wins?

[steven_wu]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

When you say visible outside the summary, what exactly is the definition of visible? I failed the find the relevant in lld that interacts with GUIDPreservedSymbols. For ld64, weak symbols are only in the GUIDPreservedSymbols when it is in the final image, so I am not sure if we share the same definition. If the weak symbols are visible outside the summary just to get coalesced away later, it doesn't have to be preserved.

I remember there were few other semantics difference in symbol resolution rules. IRLinker follows ELF visibility rules as well. It might be a good idea to clean that up sometimes.

If the ELF is choosing the most hidden version, why is the case described in the commit message a problem? Is it because weak_odr beats linkonce_odr before visibility comes into consideration?

[tejohnson]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

When you say visible outside the summary, what exactly is the definition of visible? I failed the find the relevant in lld that interacts with GUIDPreservedSymbols. For ld64, weak symbols are only in the GUIDPreservedSymbols when it is in the final image, so I am not sure if we share the same definition. If the weak symbols are visible outside the summary just to get coalesced away later, it doesn't have to be preserved.

lld doesn't create this set directly, it is done in the new LTO API here:
http://llvm-cs.pcc.me.uk/lib/LTO/LTO.cpp#910

And VisibleOutsideSummary is set here:
http://llvm-cs.pcc.me.uk/lib/LTO/LTO.cpp#539

VisibleToRegularObj is set by lld if the symbol is used in a regular (native) object
InSummary is true of the bitcode object had a summary

If the ELF is choosing the most hidden version, why is the case described in the commit message a problem? Is it because weak_odr beats linkonce_odr before visibility comes into consideration?

ELF is picking the linkonce_odr symbol (most hidden) as prevailing. If you look at the change in FunctionImport.cpp, before this patch we were unconditionally marking the prevailing linkonce_odr copy as hidden when "promoting" to weak_odr.

In the case that was failing we were first linking into a (native) shared library. The translation units in the shared library link contained both some implicit instantiations (linkonce_odr) and an explicit instantiation (weak_odr). Without LTO, the weak_odr would have resulted in a non-hidden weak definition in the shared library. Then this shared library was linked with code that contained references to this symbol that were expecting to be resolved by the explicit instantiation. If we instead mark that symbol as hidden in the shared library, those references are no longer satisfied.

[steven_wu]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

ELF is picking the linkonce_odr symbol (most hidden) as prevailing. If you look at the change in FunctionImport.cpp, before this patch we were unconditionally marking the prevailing linkonce_odr copy as hidden when "promoting" to weak_odr.

In the case that was failing we were first linking into a (native) shared library. The translation units in the shared library link contained both some implicit instantiations (linkonce_odr) and an explicit instantiation (weak_odr). Without LTO, the weak_odr would have resulted in a non-hidden weak definition in the shared library. Then this shared library was linked with code that contained references to this symbol that were expecting to be resolved by the explicit instantiation. If we instead mark that symbol as hidden in the shared library, those references are no longer satisfied.

I guess I was missing something here for how ELF handles weak links during static link time. It sounds it is correct the the linkonce_odr version is prevailing under ELF rule but I don't understand the reason why the weak_odr version is expected to be exported?

Here is my understanding for ELF linking and let me know if it is correct or not.

For linking without LTO:

• There is no bits in ELF object file to indicate auto hide. linkonce_odr and weak_odr are both weak external symbols so you get a weak copy in the dylib.

For linking with fullLTO:

• IRLinker will pick weak_odr linkage, remove unamed_addr, resulting the same output as native

For linking with thinLTO (no native or fullLTO):

• autohide disabled because weak_odr is cannot autohide, weak external symbol produced.

Since every situation produces weak external symbol, would it be easier just make lld mark weak_odr as prevailing (can you tell linkonce_odr from weak_odr in ELF object)?

Because native object for ELF doesn't have autohide optimization, missing autohide during thinLTO is not a regression.

[tejohnson]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

Sorry I forgot I hadn't responded here. @pcc should be better able to answer some of your specific questions about ELF and lld.

For linking with thinLTO (no native or fullLTO):

• autohide disabled because weak_odr is cannot autohide, weak external symbol produced.

This should also be the same as a non-LTO after the link completes - there is a non-hidden weak symbol in the library (the prevailing linkonce_odr that was "promoted" to weak_odr and now no longer marked hidden).

Since every situation produces weak external symbol, would it be easier just make lld mark weak_odr as prevailing (can you tell linkonce_odr from weak_odr in ELF object)?

I am not an expert on ELF semantics, deferring to @pcc here.

[steven_wu]

llvm/trunk/lib/LTO/LTO.cpp

334 ↗

(On Diff #199067)

I also forgot to mention here. I figure out later even for ld64, it should behave correctly even when the libLTO are not sure if the symbol can be autohide or not. It should just treat them the same as local_unname_addr.

I don't think we need to touch the logic here.

[int3]

Sorry to necro an old diff, but I'm trying to implement this behavior in LLD's Mach-O backend right now, and I'm running into some issues with ThinLTO not hiding the symbols that I expect it to. D119767: [lld-macho] Improve hiding of unnamed_addr symbols and https://discourse.llvm.org/t/mach-o-lto-handling-of-linkonce-odr-unnamed-addr/60015 have a bit more context

llvm/trunk/lib/Analysis/ModuleSummaryAnalysis.cpp

423 ↗

(On Diff #199067)

@tejohnson should we account for local_unnamed_addr constants here too? canBeOmittedFromSymbolTable() checks for both: https://github.com/llvm/llvm-project/blob/main/llvm/lib/IR/Globals.cpp#L354

[tejohnson]

llvm/trunk/lib/Analysis/ModuleSummaryAnalysis.cpp

423 ↗

(On Diff #199067)

Yes it looks like it, at least for const variables (as well as for all functions since they are const, and aliases that meet the same criteria). In fact, reading through the old comments, I see pcc asked about this and I wanted to do that as a follow up (since the previous version already only handled that case - see the change in FunctionImport.cpp), which apparently never happened. Can you send a patch to change this? Note that you will need to adjust the assert in FunctionImport.cpp. I would just change all of these places that check for LinkOnceODR && GlobalUnnamedAddr to simply call canBeOmittedFromSymbolTable().

include/llvm/IR/ModuleSummaryIndex.h

struct ValueInfo {
   bool isReadOnly() const { return RefAndFlags.getInt() & 0x2; }
   void setReadOnly() { RefAndFlags.setInt(RefAndFlags.getInt() | 0x2); }
 
   const GlobalValueSummaryMapTy::value_type *getRef() const {
     return RefAndFlags.getPointer();
   }
 
   bool isDSOLocal() const;
+
+  /// Checks if all copies are eligible for auto-hiding (have flag set).
+  bool canAutoHide() const;
 };
 
 inline raw_ostream &operator<<(raw_ostream &OS, const ValueInfo &VI) {
   OS << VI.getGUID();
   if (!VI.name().empty())
     OS << " (" << VI.name() << ")";
   return OS;
 }
struct GVFlags {
     ///
     /// In combined summary, indicate that the global value is live.
     unsigned Live : 1;
 
     /// Indicates that the linker resolved the symbol to a definition from
     /// within the same linkage unit.
     unsigned DSOLocal : 1;
 
+    /// In the per-module summary, indicates that the global value is
+    /// linkonce_odr and global unnamed addr (so eligible for auto-hiding
+    /// via hidden visibility). In the combined summary, indicates that the
+    /// prevailing linkonce_odr copy can be auto-hidden via hidden visibility
+    /// when it is upgraded to weak_odr in the backend. This is legal when
+    /// all copies are eligible for auto-hiding (i.e. all copies were
+    /// linkonce_odr global unnamed addr. If any copy is not (e.g. it was
+    /// originally weak_odr, we cannot auto-hide the prevailing copy as it
+    /// means the symbol was externally visible.
+    unsigned CanAutoHide : 1;
+
     /// Convenience Constructors
     explicit GVFlags(GlobalValue::LinkageTypes Linkage,
-                     bool NotEligibleToImport, bool Live, bool IsLocal)
+                     bool NotEligibleToImport, bool Live, bool IsLocal,
+                     bool CanAutoHide)
         : Linkage(Linkage), NotEligibleToImport(NotEligibleToImport),
-          Live(Live), DSOLocal(IsLocal) {}
+          Live(Live), DSOLocal(IsLocal), CanAutoHide(CanAutoHide) {}
   };
 
 private:
   /// Kind of summary for use in dyn_cast<> et al.
   SummaryKind Kind;
 
   GVFlags Flags;
 
public:
   bool isLive() const { return Flags.Live; }
 
   void setLive(bool Live) { Flags.Live = Live; }
 
   void setDSOLocal(bool Local) { Flags.DSOLocal = Local; }
 
   bool isDSOLocal() const { return Flags.DSOLocal; }
 
+  void setCanAutoHide(bool CanAutoHide) { Flags.CanAutoHide = CanAutoHide; }
+
+  bool canAutoHide() const { return Flags.CanAutoHide; }
+
   /// Flag that this global value cannot be imported.
   void setNotEligibleToImport() { Flags.NotEligibleToImport = true; }
 
   /// Return the list of values referenced by this global value definition.
   ArrayRef<ValueInfo> refs() const { return RefEdgeList; }
 
   /// If this is an alias summary, returns the summary of the aliased object (a
   /// global variable or function), otherwise returns itself.
public:
 
   /// Create an empty FunctionSummary (with specified call edges).
   /// Used to represent external nodes and the dummy root node.
   static FunctionSummary
   makeDummyFunctionSummary(std::vector<FunctionSummary::EdgeTy> Edges) {
     return FunctionSummary(
         FunctionSummary::GVFlags(
             GlobalValue::LinkageTypes::AvailableExternallyLinkage,
-            /*NotEligibleToImport=*/true, /*Live=*/true, /*IsLocal=*/false),
+            /*NotEligibleToImport=*/true, /*Live=*/true, /*IsLocal=*/false,
+            /*CanAutoHide=*/false),
         /*InsCount=*/0, FunctionSummary::FFlags{}, /*EntryCount=*/0,
         std::vector<ValueInfo>(), std::move(Edges),
         std::vector<GlobalValue::GUID>(),
         std::vector<FunctionSummary::VFuncId>(),
         std::vector<FunctionSummary::VFuncId>(),
         std::vector<FunctionSummary::ConstVCall>(),
         std::vector<FunctionSummary::ConstVCall>());
   }

include/llvm/IR/ModuleSummaryIndexYAML.h

template <> struct MappingTraits<TypeIdSummary> {
   static void mapping(IO &io, TypeIdSummary& summary) {
     io.mapOptional("TTRes", summary.TTRes);
     io.mapOptional("WPDRes", summary.WPDRes);
   }
 };
 
 struct FunctionSummaryYaml {
   unsigned Linkage;
-  bool NotEligibleToImport, Live, IsLocal;
+  bool NotEligibleToImport, Live, IsLocal, CanAutoHide;
   std::vector<uint64_t> Refs;
   std::vector<uint64_t> TypeTests;
   std::vector<FunctionSummary::VFuncId> TypeTestAssumeVCalls,
       TypeCheckedLoadVCalls;
   std::vector<FunctionSummary::ConstVCall> TypeTestAssumeConstVCalls,
       TypeCheckedLoadConstVCalls;
 };
 

 namespace yaml {
 
 template <> struct MappingTraits<FunctionSummaryYaml> {
   static void mapping(IO &io, FunctionSummaryYaml& summary) {
     io.mapOptional("Linkage", summary.Linkage);
     io.mapOptional("NotEligibleToImport", summary.NotEligibleToImport);
     io.mapOptional("Live", summary.Live);
     io.mapOptional("Local", summary.IsLocal);
+    io.mapOptional("CanAutoHide", summary.CanAutoHide);
     io.mapOptional("Refs", summary.Refs);
     io.mapOptional("TypeTests", summary.TypeTests);
     io.mapOptional("TypeTestAssumeVCalls", summary.TypeTestAssumeVCalls);
     io.mapOptional("TypeCheckedLoadVCalls", summary.TypeCheckedLoadVCalls);
     io.mapOptional("TypeTestAssumeConstVCalls",
                    summary.TypeTestAssumeConstVCalls);
     io.mapOptional("TypeCheckedLoadConstVCalls",
                    summary.TypeCheckedLoadConstVCalls);
for (auto &FSum : FSums) {
       for (auto &RefGUID : FSum.Refs) {
         if (!V.count(RefGUID))
           V.emplace(RefGUID, /*IsAnalysis=*/false);
         Refs.push_back(ValueInfo(/*IsAnalysis=*/false, &*V.find(RefGUID)));
       }
       Elem.SummaryList.push_back(llvm::make_unique<FunctionSummary>(
           GlobalValueSummary::GVFlags(
               static_cast<GlobalValue::LinkageTypes>(FSum.Linkage),
-              FSum.NotEligibleToImport, FSum.Live, FSum.IsLocal),
+              FSum.NotEligibleToImport, FSum.Live, FSum.IsLocal, FSum.CanAutoHide),
           /*NumInsts=*/0, FunctionSummary::FFlags{}, /*EntryCount=*/0, Refs,
           ArrayRef<FunctionSummary::EdgeTy>{}, std::move(FSum.TypeTests),
           std::move(FSum.TypeTestAssumeVCalls),
           std::move(FSum.TypeCheckedLoadVCalls),
           std::move(FSum.TypeTestAssumeConstVCalls),
           std::move(FSum.TypeCheckedLoadConstVCalls)));
     }
   }
   static void output(IO &io, GlobalValueSummaryMapTy &V) {
     for (auto &P : V) {
       std::vector<FunctionSummaryYaml> FSums;
       for (auto &Sum : P.second.SummaryList) {
         if (auto *FSum = dyn_cast<FunctionSummary>(Sum.get())) {
           std::vector<uint64_t> Refs;
           for (auto &VI : FSum->refs())
             Refs.push_back(VI.getGUID());
           FSums.push_back(FunctionSummaryYaml{
               FSum->flags().Linkage,
               static_cast<bool>(FSum->flags().NotEligibleToImport),
               static_cast<bool>(FSum->flags().Live),
-              static_cast<bool>(FSum->flags().DSOLocal), Refs,
+              static_cast<bool>(FSum->flags().DSOLocal),
+              static_cast<bool>(FSum->flags().CanAutoHide), Refs,
               FSum->type_tests(), FSum->type_test_assume_vcalls(),
               FSum->type_checked_load_vcalls(),
               FSum->type_test_assume_const_vcalls(),
               FSum->type_checked_load_const_vcalls()});
           }
       }
       if (!FSums.empty())
         io.mapRequired(llvm::utostr(P.first).c_str(), FSums);

include/llvm/LTO/LTO.h

 ///
 /// This is done for correctness (if value exported, ensure we always
 /// emit a copy), and compile-time optimization (allow drop of duplicates).
 void thinLTOResolvePrevailingInIndex(
     ModuleSummaryIndex &Index,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing,
     function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
-        recordNewLinkage);
+        recordNewLinkage,
+    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols);
 
 /// Update the linkages in the given \p Index to mark exported values
 /// as external and non-exported values as internal. The ThinLTO backends
 /// must apply the changes to the Module via thinLTOInternalizeModule.
 void thinLTOInternalizeAndPromoteInIndex(
     ModuleSummaryIndex &Index,
     function_ref<bool(StringRef, GlobalValue::GUID)> isExported);
 
addRegularLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
                 const SymbolResolution *&ResI, const SymbolResolution *ResE);
   Error linkRegularLTO(RegularLTOState::AddedModule Mod,
                        bool LivenessFromIndex);
 
   Error addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
                    const SymbolResolution *&ResI, const SymbolResolution *ResE);
 
   Error runRegularLTO(AddStreamFn AddStream);
-  Error runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache);
+  Error runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
+                   const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols);
 
   Error checkPartiallySplit();
 
   mutable bool CalledGetMaxTasks = false;
 
   // Use Optional to distinguish false from not yet initialized.
   Optional<bool> EnableSplitLTOUnit;
 };

lib/Analysis/ModuleSummaryAnalysis.cpp

CallGraphEdges[Index.getOrInsertValueInfo(I)].updateHotness(
         ForceSummaryEdgesCold == FunctionSummary::FSHT_All
             ? CalleeInfo::HotnessType::Cold
             : CalleeInfo::HotnessType::Critical);
 
   bool NonRenamableLocal = isNonRenamableLocal(F);
   bool NotEligibleForImport =
       NonRenamableLocal || HasInlineAsmMaybeReferencingInternal;
   GlobalValueSummary::GVFlags Flags(F.getLinkage(), NotEligibleForImport,
-                                    /* Live = */ false, F.isDSOLocal());
+                                    /* Live = */ false, F.isDSOLocal(),
+                                    F.hasLinkOnceODRLinkage() && F.hasGlobalUnnamedAddr());
   FunctionSummary::FFlags FunFlags{
       F.hasFnAttribute(Attribute::ReadNone),
       F.hasFnAttribute(Attribute::ReadOnly),
       F.hasFnAttribute(Attribute::NoRecurse), F.returnDoesNotAlias(),
       // FIXME: refactor this to use the same code that inliner is using.
       // Don't try to import functions with noinline attribute.
       F.getAttributes().hasFnAttribute(Attribute::NoInline)};
   auto FuncSummary = llvm::make_unique<FunctionSummary>(

 static void
 computeVariableSummary(ModuleSummaryIndex &Index, const GlobalVariable &V,
                        DenseSet<GlobalValue::GUID> &CantBePromoted) {
   SetVector<ValueInfo> RefEdges;
   SmallPtrSet<const User *, 8> Visited;
   bool HasBlockAddress = findRefEdges(Index, &V, RefEdges, Visited);
   bool NonRenamableLocal = isNonRenamableLocal(V);
   GlobalValueSummary::GVFlags Flags(V.getLinkage(), NonRenamableLocal,
-                                    /* Live = */ false, V.isDSOLocal());
+                                    /* Live = */ false, V.isDSOLocal(),
+                                    V.hasLinkOnceODRLinkage() && V.hasGlobalUnnamedAddr());
 
   // Don't mark variables we won't be able to internalize as read-only.
   GlobalVarSummary::GVarFlags VarFlags(
       !V.hasComdat() && !V.hasAppendingLinkage() && !V.isInterposable() &&
       !V.hasAvailableExternallyLinkage() && !V.hasDLLExportStorageClass());
   auto GVarSummary = llvm::make_unique<GlobalVarSummary>(Flags, VarFlags,
                                                          RefEdges.takeVector());
   if (NonRenamableLocal)
     CantBePromoted.insert(V.getGUID());
   if (HasBlockAddress)
     GVarSummary->setNotEligibleToImport();
   Index.addGlobalValueSummary(V, std::move(GVarSummary));
 }
 
 static void
 computeAliasSummary(ModuleSummaryIndex &Index, const GlobalAlias &A,
                     DenseSet<GlobalValue::GUID> &CantBePromoted) {
   bool NonRenamableLocal = isNonRenamableLocal(A);
   GlobalValueSummary::GVFlags Flags(A.getLinkage(), NonRenamableLocal,
-                                    /* Live = */ false, A.isDSOLocal());
+                                    /* Live = */ false, A.isDSOLocal(),
+                                    A.hasLinkOnceODRLinkage() && A.hasGlobalUnnamedAddr());
   auto AS = llvm::make_unique<AliasSummary>(Flags);
   auto *Aliasee = A.getBaseObject();
   auto AliaseeVI = Index.getValueInfo(Aliasee->getGUID());
   assert(AliaseeVI && "Alias expects aliasee summary to be available");
   assert(AliaseeVI.getSummaryList().size() == 1 &&
          "Expected a single entry per aliasee in per-module index");
   AS->setAliasee(AliaseeVI, AliaseeVI.getSummaryList()[0].get());
   if (NonRenamableLocal)
ModuleSymbolTable::CollectAsmSymbols(
           HasLocalInlineAsmSymbol = true;
           GlobalValue *GV = M.getNamedValue(Name);
           if (!GV)
             return;
           assert(GV->isDeclaration() && "Def in module asm already has definition");
           GlobalValueSummary::GVFlags GVFlags(GlobalValue::InternalLinkage,
                                               /* NotEligibleToImport = */ true,
                                               /* Live = */ true,
-                                              /* Local */ GV->isDSOLocal());
+                                              /* Local */ GV->isDSOLocal(),
+                                              GV->hasLinkOnceODRLinkage() && GV->hasGlobalUnnamedAddr());
           CantBePromoted.insert(GV->getGUID());
           // Create the appropriate summary type.
           if (Function *F = dyn_cast<Function>(GV)) {
             std::unique_ptr<FunctionSummary> Summary =
                 llvm::make_unique<FunctionSummary>(
                     GVFlags, /*InstCount=*/0,
                     FunctionSummary::FFlags{
                         F->hasFnAttribute(Attribute::ReadNone),

lib/AsmParser/LLLexer.cpp

#define KEYWORD(STR)                                                           \
   KEYWORD(guid);
   KEYWORD(name);
   KEYWORD(summaries);
   KEYWORD(flags);
   KEYWORD(linkage);
   KEYWORD(notEligibleToImport);
   KEYWORD(live);
   KEYWORD(dsoLocal);
+  KEYWORD(canAutoHide);
   KEYWORD(function);
   KEYWORD(insts);
   KEYWORD(funcFlags);
   KEYWORD(readNone);
   KEYWORD(readOnly);
   KEYWORD(noRecurse);
   KEYWORD(returnDoesNotAlias);
   KEYWORD(noInline);

lib/AsmParser/LLParser.cpp

 bool LLParser::ParseFunctionSummary(std::string Name, GlobalValue::GUID GUID,
                                     unsigned ID) {
   assert(Lex.getKind() == lltok::kw_function);
   Lex.Lex();
 
   StringRef ModulePath;
   GlobalValueSummary::GVFlags GVFlags = GlobalValueSummary::GVFlags(
       /*Linkage=*/GlobalValue::ExternalLinkage, /*NotEligibleToImport=*/false,
-      /*Live=*/false, /*IsLocal=*/false);
+      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false);
   unsigned InstCount;
   std::vector<FunctionSummary::EdgeTy> Calls;
   FunctionSummary::TypeIdInfo TypeIdInfo;
   std::vector<ValueInfo> Refs;
   // Default is all-zeros (conservative values).
   FunctionSummary::FFlags FFlags = {};
   if (ParseToken(lltok::colon, "expected ':' here") ||
       ParseToken(lltok::lparen, "expected '(' here") ||

 bool LLParser::ParseVariableSummary(std::string Name, GlobalValue::GUID GUID,
                                     unsigned ID) {
   assert(Lex.getKind() == lltok::kw_variable);
   Lex.Lex();
 
   StringRef ModulePath;
   GlobalValueSummary::GVFlags GVFlags = GlobalValueSummary::GVFlags(
       /*Linkage=*/GlobalValue::ExternalLinkage, /*NotEligibleToImport=*/false,
-      /*Live=*/false, /*IsLocal=*/false);
+      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false);
   GlobalVarSummary::GVarFlags GVarFlags(/*ReadOnly*/ false);
   std::vector<ValueInfo> Refs;
   if (ParseToken(lltok::colon, "expected ':' here") ||
       ParseToken(lltok::lparen, "expected '(' here") ||
       ParseModuleReference(ModulePath) ||
       ParseToken(lltok::comma, "expected ',' here") || ParseGVFlags(GVFlags) ||
       ParseToken(lltok::comma, "expected ',' here") ||
       ParseGVarFlags(GVarFlags))
bool LLParser::ParseAliasSummary(std::string Name, GlobalValue::GUID GUID,
                                  unsigned ID) {
   assert(Lex.getKind() == lltok::kw_alias);
   LocTy Loc = Lex.getLoc();
   Lex.Lex();
 
   StringRef ModulePath;
   GlobalValueSummary::GVFlags GVFlags = GlobalValueSummary::GVFlags(
       /*Linkage=*/GlobalValue::ExternalLinkage, /*NotEligibleToImport=*/false,
-      /*Live=*/false, /*IsLocal=*/false);
+      /*Live=*/false, /*IsLocal=*/false, /*CanAutoHide=*/false);
   if (ParseToken(lltok::colon, "expected ':' here") ||
       ParseToken(lltok::lparen, "expected '(' here") ||
       ParseModuleReference(ModulePath) ||
       ParseToken(lltok::comma, "expected ',' here") || ParseGVFlags(GVFlags) ||
       ParseToken(lltok::comma, "expected ',' here") ||
       ParseToken(lltok::kw_aliasee, "expected 'aliasee' here") ||
       ParseToken(lltok::colon, "expected ':' here"))
     return true;
if (ParseToken(lltok::comma, "expected ',' here") ||
     return true;
 
   return false;
 }
 
 /// GVFlags
 ///   ::= 'flags' ':' '(' 'linkage' ':' OptionalLinkageAux ','
 ///         'notEligibleToImport' ':' Flag ',' 'live' ':' Flag ','
-///         'dsoLocal' ':' Flag ')'
+///         'dsoLocal' ':' Flag ',' 'canAutoHide' ':' Flag ')'
 bool LLParser::ParseGVFlags(GlobalValueSummary::GVFlags &GVFlags) {
   assert(Lex.getKind() == lltok::kw_flags);
   Lex.Lex();
 
-  bool HasLinkage;
   if (ParseToken(lltok::colon, "expected ':' here") ||
-      ParseToken(lltok::lparen, "expected '(' here") ||
-      ParseToken(lltok::kw_linkage, "expected 'linkage' here") ||
-      ParseToken(lltok::colon, "expected ':' here"))
+      ParseToken(lltok::lparen, "expected '(' here"))
     return true;
 
+  do {
+    unsigned Flag;
+    switch (Lex.getKind()) {
+    case lltok::kw_linkage:
+      Lex.Lex();
+      if (ParseToken(lltok::colon, "expected ':'"))
+        return true;
+      bool HasLinkage;
       GVFlags.Linkage = parseOptionalLinkageAux(Lex.getKind(), HasLinkage);
       assert(HasLinkage && "Linkage not optional in summary entry");
       Lex.Lex();
-
-  unsigned Flag;
-  if (ParseToken(lltok::comma, "expected ',' here") ||
-      ParseToken(lltok::kw_notEligibleToImport,
-                 "expected 'notEligibleToImport' here") ||
-      ParseToken(lltok::colon, "expected ':' here") || ParseFlag(Flag))
+      break;
+    case lltok::kw_notEligibleToImport:
+      Lex.Lex();
+      if (ParseToken(lltok::colon, "expected ':'") || ParseFlag(Flag))
         return true;
       GVFlags.NotEligibleToImport = Flag;
-
-  if (ParseToken(lltok::comma, "expected ',' here") ||
-      ParseToken(lltok::kw_live, "expected 'live' here") ||
-      ParseToken(lltok::colon, "expected ':' here") || ParseFlag(Flag))
+      break;
+    case lltok::kw_live:
+      Lex.Lex();
+      if (ParseToken(lltok::colon, "expected ':'") || ParseFlag(Flag))
         return true;
       GVFlags.Live = Flag;
-
-  if (ParseToken(lltok::comma, "expected ',' here") ||
-      ParseToken(lltok::kw_dsoLocal, "expected 'dsoLocal' here") ||
-      ParseToken(lltok::colon, "expected ':' here") || ParseFlag(Flag))
+      break;
+    case lltok::kw_dsoLocal:
+      Lex.Lex();
+      if (ParseToken(lltok::colon, "expected ':'") || ParseFlag(Flag))
         return true;
       GVFlags.DSOLocal = Flag;
+      break;
+    case lltok::kw_canAutoHide:
+      Lex.Lex();
+      if (ParseToken(lltok::colon, "expected ':'") || ParseFlag(Flag))
+        return true;
+      GVFlags.CanAutoHide = Flag;
+      break;
+    default:
+      return Error(Lex.getLoc(), "expected gv flag type");
+    }
+  } while (EatIfPresent(lltok::comma));
 
   if (ParseToken(lltok::rparen, "expected ')' here"))
     return true;
 
   return false;
 }
 
 /// GVarFlags

lib/AsmParser/LLToken.h

enum Kind {
   kw_guid,
   kw_name,
   kw_summaries,
   kw_flags,
   kw_linkage,
   kw_notEligibleToImport,
   kw_live,
   kw_dsoLocal,
+  kw_canAutoHide,
   kw_function,
   kw_insts,
   kw_funcFlags,
   kw_readNone,
   kw_readOnly,
   kw_noRecurse,
   kw_returnDoesNotAlias,
   kw_noInline,

lib/Bitcode/Reader/BitcodeReader.cpp

static GlobalValueSummary::GVFlags getDecodedGVSummaryFlags(uint64_t RawFlags,
   auto Linkage = GlobalValue::LinkageTypes(RawFlags & 0xF); // 4 bits
   RawFlags = RawFlags >> 4;
   bool NotEligibleToImport = (RawFlags & 0x1) || Version < 3;
   // The Live flag wasn't introduced until version 3. For dead stripping
   // to work correctly on earlier versions, we must conservatively treat all
   // values as live.
   bool Live = (RawFlags & 0x2) || Version < 3;
   bool Local = (RawFlags & 0x4);
+  bool AutoHide = (RawFlags & 0x8);
 
-  return GlobalValueSummary::GVFlags(Linkage, NotEligibleToImport, Live, Local);
+  return GlobalValueSummary::GVFlags(Linkage, NotEligibleToImport, Live, Local, AutoHide);
 }
 
 // Decode the flags for GlobalVariable in the summary
 static GlobalVarSummary::GVarFlags getDecodedGVarFlags(uint64_t RawFlags) {
   return GlobalVarSummary::GVarFlags((RawFlags & 0x1) ? true : false);
 }
 
 static GlobalValue::VisibilityTypes getDecodedVisibility(unsigned Val) {

lib/Bitcode/Writer/BitcodeWriter.cpp

 
 // Decode the flags for GlobalValue in the summary
 static uint64_t getEncodedGVSummaryFlags(GlobalValueSummary::GVFlags Flags) {
   uint64_t RawFlags = 0;
 
   RawFlags |= Flags.NotEligibleToImport; // bool
   RawFlags |= (Flags.Live << 1);
   RawFlags |= (Flags.DSOLocal << 2);
+  RawFlags |= (Flags.CanAutoHide << 3);
 
   // Linkage don't need to be remapped at that time for the summary. Any future
   // change to the getEncodedLinkage() function will need to be taken into
   // account here as well.
   RawFlags = (RawFlags << 4) | Flags.Linkage; // 4 bits
 
   return RawFlags;
 }

lib/IR/AsmWriter.cpp

void AssemblyWriter::printSummary(const GlobalValueSummary &Summary) {
   GlobalValue::LinkageTypes LT = (GlobalValue::LinkageTypes)GVFlags.Linkage;
   Out << getSummaryKindName(Summary.getSummaryKind()) << ": ";
   Out << "(module: ^" << Machine.getModulePathSlot(Summary.modulePath())
       << ", flags: (";
   Out << "linkage: " << getLinkageName(LT);
   Out << ", notEligibleToImport: " << GVFlags.NotEligibleToImport;
   Out << ", live: " << GVFlags.Live;
   Out << ", dsoLocal: " << GVFlags.DSOLocal;
+  Out << ", canAutoHide: " << GVFlags.CanAutoHide;
   Out << ")";
 
   if (Summary.getSummaryKind() == GlobalValueSummary::AliasKind)
     printAliasSummary(cast<AliasSummary>(&Summary));
   else if (Summary.getSummaryKind() == GlobalValueSummary::FunctionKind)
     printFunctionSummary(cast<FunctionSummary>(&Summary));
   else
     printGlobalVarSummary(cast<GlobalVarSummary>(&Summary));

lib/IR/ModuleSummaryIndex.cpp

 
 #define DEBUG_TYPE "module-summary-index"
 
 STATISTIC(ReadOnlyLiveGVars,
           "Number of live global variables marked read only");
 
 FunctionSummary FunctionSummary::ExternalNode =
     FunctionSummary::makeDummyFunctionSummary({});
+
 bool ValueInfo::isDSOLocal() const {
   // Need to check all summaries are local in case of hash collisions.
   return getSummaryList().size() &&
          llvm::all_of(getSummaryList(),
                       [](const std::unique_ptr<GlobalValueSummary> &Summary) {
                         return Summary->isDSOLocal();
                       });
 }
 
+bool ValueInfo::canAutoHide() const {
+  // Can only auto hide if all copies are eligible to auto hide.
+  return getSummaryList().size() &&
+         llvm::all_of(getSummaryList(),
+                      [](const std::unique_ptr<GlobalValueSummary> &Summary) {
+                        return Summary->canAutoHide();
+                      });
+}
+
 // Gets the number of immutable refs in RefEdgeList
 unsigned FunctionSummary::immutableRefCount() const {
   // Here we take advantage of having all readonly references
   // located in the end of the RefEdgeList.
   auto Refs = refs();
   unsigned ImmutableRefCnt = 0;
   for (int I = Refs.size() - 1; I >= 0 && Refs[I].isReadOnly(); --I)
     ImmutableRefCnt++;
for (auto &SummaryIt : GVSMap) {
       } else if (isa<AliasSummary>(SummaryIt.second)) {
         A.add("style", "dotted,filled", "alias");
         A.add("shape", "box");
       } else {
         A.add("shape", "Mrecord", "variable");
         if (Flags.Live && hasReadOnlyFlag(SummaryIt.second))
           A.addComment("immutable");
       }
+      if (Flags.DSOLocal)
+        A.addComment("dsoLocal");
+      if (Flags.CanAutoHide)
+        A.addComment("canAutoHide");
 
       auto VI = getValueInfo(SummaryIt.first);
       A.add("label", getNodeLabel(VI, SummaryIt.second));
       if (!Flags.Live)
         A.add("fillcolor", "red", "dead");
       else if (Flags.NotEligibleToImport)
         A.add("fillcolor", "yellow", "not eligible to import");
 

lib/LTO/LTO.cpp

if (CfiFunctionDefs.count(ValueGUID))
       UsedCfiDefs.insert(ValueGUID);
     if (CfiFunctionDecls.count(ValueGUID))
       UsedCfiDecls.insert(ValueGUID);
   };
 
   auto AddUsedThings = [&](GlobalValueSummary *GS) {
     if (!GS) return;
     AddUnsigned(GS->isLive());
+    AddUnsigned(GS->canAutoHide());
     for (const ValueInfo &VI : GS->refs()) {
       AddUnsigned(VI.isDSOLocal());
       AddUsedCfiGlobal(VI.getGUID());
     }
     if (auto *GVS = dyn_cast<GlobalVarSummary>(GS))
       AddUnsigned(GVS->isReadOnly());
     if (auto *FS = dyn_cast<FunctionSummary>(GS)) {
       for (auto &TT : FS->type_tests())
if (FileOrErr) {
       }
     }
   }
 
   Key = toHex(Hasher.result());
 }
 
 static void thinLTOResolvePrevailingGUID(
-    GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
-    DenseSet<GlobalValueSummary *> &GlobalInvolvedWithAlias,
+    ValueInfo VI, DenseSet<GlobalValueSummary *> &GlobalInvolvedWithAlias,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing,
     function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
-        recordNewLinkage) {
-  for (auto &S : GVSummaryList) {
+        recordNewLinkage,
+    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
+  for (auto &S : VI.getSummaryList()) {
     GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
     // Ignore local and appending linkage values since the linker
     // doesn't resolve them.
     if (GlobalValue::isLocalLinkage(OriginalLinkage) ||
         GlobalValue::isAppendingLinkage(S->linkage()))
       continue;
     // We need to emit only one of these. The prevailing module will keep it,
     // but turned into a weak, while the others will drop it when possible.
     // This is both a compile-time optimization and a correctness
     // transformation. This is necessary for correctness when we have exported
     // a reference - we need to convert the linkonce to weak to
     // ensure a copy is kept to satisfy the exported reference.
     // FIXME: We may want to split the compile time and correctness
     // aspects into separate routines.
-    if (isPrevailing(GUID, S.get())) {
-      if (GlobalValue::isLinkOnceLinkage(OriginalLinkage))
+    if (isPrevailing(VI.getGUID(), S.get())) {
+      if (GlobalValue::isLinkOnceLinkage(OriginalLinkage)) {
         S->setLinkage(GlobalValue::getWeakLinkage(
             GlobalValue::isLinkOnceODRLinkage(OriginalLinkage)));
+        // The kept copy is eligible for auto-hiding (hidden visibility) if all
+        // copies were (i.e. they were all linkonce_odr global unnamed addr).
+        // If any copy is not (e.g. it was originally weak_odr), then the symbol
+        // must remain externally available (e.g. a weak_odr from an explicitly
+        // instantiated template). Additionally, if it is in the
+        // GUIDPreservedSymbols set, that means that it is visibile outside
+        // the summary (e.g. in a native object or a bitcode file without
+        // summary), and in that case we cannot hide it as it isn't possible to
+        // check all copies.
+        S->setCanAutoHide(VI.canAutoHide() &&
+                          !GUIDPreservedSymbols.count(VI.getGUID()));
+      }
     }
     // Alias and aliasee can't be turned into available_externally.
     else if (!isa<AliasSummary>(S.get()) &&
              !GlobalInvolvedWithAlias.count(S.get()))
       S->setLinkage(GlobalValue::AvailableExternallyLinkage);
     if (S->linkage() != OriginalLinkage)
-      recordNewLinkage(S->modulePath(), GUID, S->linkage());
+      recordNewLinkage(S->modulePath(), VI.getGUID(), S->linkage());
   }
 }
 
 /// Resolve linkage for prevailing symbols in the \p Index.
 //
 // We'd like to drop these functions if they are no longer referenced in the
 // current module. However there is a chance that another module is still
 // referencing them because of the import. We make sure we always emit at least
 // one copy.
 void llvm::thinLTOResolvePrevailingInIndex(
     ModuleSummaryIndex &Index,
     function_ref<bool(GlobalValue::GUID, const GlobalValueSummary *)>
         isPrevailing,
     function_ref<void(StringRef, GlobalValue::GUID, GlobalValue::LinkageTypes)>
-        recordNewLinkage) {
+        recordNewLinkage,
+    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
   // We won't optimize the globals that are referenced by an alias for now
   // Ideally we should turn the alias into a global and duplicate the definition
   // when needed.
   DenseSet<GlobalValueSummary *> GlobalInvolvedWithAlias;
   for (auto &I : Index)
     for (auto &S : I.second.SummaryList)
       if (auto AS = dyn_cast<AliasSummary>(S.get()))
         GlobalInvolvedWithAlias.insert(&AS->getAliasee());
 
   for (auto &I : Index)
-    thinLTOResolvePrevailingGUID(I.second.SummaryList, I.first,
-                                 GlobalInvolvedWithAlias, isPrevailing,
-                                 recordNewLinkage);
+    thinLTOResolvePrevailingGUID(Index.getValueInfo(I), GlobalInvolvedWithAlias,
+                                 isPrevailing, recordNewLinkage,
+                                 GUIDPreservedSymbols);
 }
 
 static void thinLTOInternalizeAndPromoteGUID(
     GlobalValueSummaryList &GVSummaryList, GlobalValue::GUID GUID,
     function_ref<bool(StringRef, GlobalValue::GUID)> isExported) {
   for (auto &S : GVSummaryList) {
     if (isExported(S->modulePath(), GUID)) {
       if (GlobalValue::isLocalLinkage(S->linkage()))
if (Error Err = linkRegularLTO(std::move(M),
       return Err;
 
   // Ensure we don't have inconsistently split LTO units with type tests.
   if (Error Err = checkPartiallySplit())
     return Err;
 
   Error Result = runRegularLTO(AddStream);
   if (!Result)
-    Result = runThinLTO(AddStream, Cache);
+    Result = runThinLTO(AddStream, Cache, GUIDPreservedSymbols);
 
   if (StatsFile)
     PrintStatisticsJSON(StatsFile->os());
 
   return Result;
 }
 
 Error LTO::runRegularLTO(AddStreamFn AddStream) {
return [=](Config &Conf, ModuleSummaryIndex &CombinedIndex,
              const StringMap<GVSummaryMapTy> &ModuleToDefinedGVSummaries,
              AddStreamFn AddStream, NativeObjectCache Cache) {
     return llvm::make_unique<WriteIndexesThinBackend>(
         Conf, CombinedIndex, ModuleToDefinedGVSummaries, OldPrefix, NewPrefix,
         ShouldEmitImportsFiles, LinkedObjectsFile, OnWrite);
   };
 }
 
-Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache) {
+Error LTO::runThinLTO(AddStreamFn AddStream, NativeObjectCache Cache,
+                      const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
   if (ThinLTO.ModuleMap.empty())
     return Error::success();
 
   if (Conf.CombinedIndexHook && !Conf.CombinedIndexHook(ThinLTO.CombinedIndex))
     return Error::success();
 
   // Collect for each module the list of function it defines (GUID ->
   // Summary).
auto isPrevailing = [&](GlobalValue::GUID GUID,
     return ThinLTO.PrevailingModuleForGUID[GUID] == S->modulePath();
   };
   auto recordNewLinkage = [&](StringRef ModuleIdentifier,
                               GlobalValue::GUID GUID,
                               GlobalValue::LinkageTypes NewLinkage) {
     ResolvedODR[ModuleIdentifier][GUID] = NewLinkage;
   };
   thinLTOResolvePrevailingInIndex(ThinLTO.CombinedIndex, isPrevailing,
-                                  recordNewLinkage);
+                                  recordNewLinkage, GUIDPreservedSymbols);
 
   std::unique_ptr<ThinBackendProc> BackendProc =
       ThinLTO.Backend(Conf, ThinLTO.CombinedIndex, ModuleToDefinedGVSummaries,
                       AddStream, Cache);
 
   // Tasks 0 through ParallelCodeGenParallelismLevel-1 are reserved for combined
   // module and parallel code generation partitions.
   unsigned Task = RegularLTO.ParallelCodeGenParallelismLevel;

lib/LTO/ThinLTOCodeGenerator.cpp

 /// Resolve prevailing symbols. Record resolutions in the \p ResolvedODR map
 /// for caching, and in the \p Index for application during the ThinLTO
 /// backends. This is needed for correctness for exported symbols (ensure
 /// at least one copy kept) and a compile-time optimization (to drop duplicate
 /// copies when possible).
 static void resolvePrevailingInIndex(
     ModuleSummaryIndex &Index,
     StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>>
-        &ResolvedODR) {
+        &ResolvedODR,
+    const DenseSet<GlobalValue::GUID> &GUIDPreservedSymbols) {
 
   DenseMap<GlobalValue::GUID, const GlobalValueSummary *> PrevailingCopy;
   computePrevailingCopies(Index, PrevailingCopy);
 
   auto isPrevailing = [&](GlobalValue::GUID GUID, const GlobalValueSummary *S) {
     const auto &Prevailing = PrevailingCopy.find(GUID);
     // Not in map means that there was only one copy, which must be prevailing.
     if (Prevailing == PrevailingCopy.end())
       return true;
     return Prevailing->second == S;
   };
 
   auto recordNewLinkage = [&](StringRef ModuleIdentifier,
                               GlobalValue::GUID GUID,
                               GlobalValue::LinkageTypes NewLinkage) {
     ResolvedODR[ModuleIdentifier][GUID] = NewLinkage;
   };
 
-  thinLTOResolvePrevailingInIndex(Index, isPrevailing, recordNewLinkage);
+  thinLTOResolvePrevailingInIndex(Index, isPrevailing, recordNewLinkage,
+                                  GUIDPreservedSymbols);
 }
 
 // Initialize the TargetMachine builder for a given Triple
 static void initTMBuilder(TargetMachineBuilder &TMBuilder,
                           const Triple &TheTriple) {
   // Set a default CPU for Darwin triples (copied from LTOCodeGenerator).
   // FIXME this looks pretty terrible...
   if (TMBuilder.MCpu.empty() && TheTriple.isOSDarwin()) {
void ThinLTOCodeGenerator::promote(Module &TheModule,
   // Generate import/export list
   StringMap<FunctionImporter::ImportMapTy> ImportLists(ModuleCount);
   StringMap<FunctionImporter::ExportSetTy> ExportLists(ModuleCount);
   ComputeCrossModuleImport(Index, ModuleToDefinedGVSummaries, ImportLists,
                            ExportLists);
 
   // Resolve prevailing symbols
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
-  resolvePrevailingInIndex(Index, ResolvedODR);
+  resolvePrevailingInIndex(Index, ResolvedODR, GUIDPreservedSymbols);
 
   thinLTOResolvePrevailingInModule(
       TheModule, ModuleToDefinedGVSummaries[ModuleIdentifier]);
 
   // Promote the exported values in the index, so that they are promoted
   // in the module.
   internalizeAndPromoteInIndex(ExportLists, GUIDPreservedSymbols, Index);
 
void ThinLTOCodeGenerator::run() {
   // We use a std::map here to be able to have a defined ordering when
   // producing a hash for the cache entry.
   // FIXME: we should be able to compute the caching hash for the entry based
   // on the index, and nuke this map.
   StringMap<std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>> ResolvedODR;
 
   // Resolve prevailing symbols, this has to be computed early because it
   // impacts the caching.
-  resolvePrevailingInIndex(*Index, ResolvedODR);
+  resolvePrevailingInIndex(*Index, ResolvedODR, GUIDPreservedSymbols);
 
   // Use global summary-based analysis to identify symbols that can be
   // internalized (because they aren't exported or preserved as per callback).
   // Changes are made in the index, consumed in the ThinLTO backends.
   internalizeAndPromoteInIndex(ExportLists, GUIDPreservedSymbols, *Index);
 
   // Make sure that every module has an entry in the ExportLists, ImportList,
   // GVSummary and ResolvedODR maps to enable threaded access to these maps

lib/Transforms/IPO/FunctionImport.cpp

auto updateLinkage = [&](GlobalValue &GV) {
     if (GlobalValue::isAvailableExternallyLinkage(NewLinkage) &&
         GlobalValue::isInterposableLinkage(GV.getLinkage())) {
       if (!convertToDeclaration(GV))
         // FIXME: Change this to collect replaced GVs and later erase
         // them from the parent module once thinLTOResolvePrevailingGUID is
         // changed to enable this for aliases.
         llvm_unreachable("Expected GV to be converted");
     } else {
-      // If the original symbols has global unnamed addr and linkonce_odr linkage,
-      // it should be an auto hide symbol. Add hidden visibility to the symbol to
-      // preserve the property.
-      if (GV.hasLinkOnceODRLinkage() && GV.hasGlobalUnnamedAddr() &&
-          NewLinkage == GlobalValue::WeakODRLinkage)
+      // If all copies of the original symbol had global unnamed addr and
+      // linkonce_odr linkage, it should be an auto hide symbol. In that case
+      // the thin link would have marked it as CanAutoHide. Add hidden visibility
+      // to the symbol to preserve the property.
+      if (NewLinkage == GlobalValue::WeakODRLinkage &&
+          GS->second->canAutoHide()) {
+        assert(GV.hasLinkOnceODRLinkage() && GV.hasGlobalUnnamedAddr());
         GV.setVisibility(GlobalValue::HiddenVisibility);
+      }
 
       LLVM_DEBUG(dbgs() << "ODR fixing up linkage for `" << GV.getName()
                         << "` from " << GV.getLinkage() << " to " << NewLinkage
                         << "\n");
       GV.setLinkage(NewLinkage);
     }
     // Remove declarations from comdats, including available_externally
     // as this is a declaration for the linker, and will be dropped eventually.

test/Assembler/thinlto-summary.ll

 
 ; Summaries with different linkage types.
 ^4 = gv: (guid: 3, summaries: (function: (module: ^0, flags: (linkage: internal, notEligibleToImport: 0, live: 0, dsoLocal: 1), insts: 1)))
 ; Make this one an alias with a forward reference to aliasee.
 ^5 = gv: (guid: 4, summaries: (alias: (module: ^0, flags: (linkage: private, notEligibleToImport: 0, live: 0, dsoLocal: 1), aliasee: ^14)))
 ^6 = gv: (guid: 5, summaries: (function: (module: ^0, flags: (linkage: available_externally, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
 ^7 = gv: (guid: 6, summaries: (function: (module: ^0, flags: (linkage: linkonce, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
 ^8 = gv: (guid: 7, summaries: (function: (module: ^0, flags: (linkage: linkonce_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-^9 = gv: (guid: 8, summaries: (function: (module: ^0, flags: (linkage: weak_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
+^9 = gv: (guid: 8, summaries: (function: (module: ^0, flags: (linkage: weak_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 1), insts: 1)))
 ^10 = gv: (guid: 9, summaries: (function: (module: ^0, flags: (linkage: weak, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
 ^11 = gv: (guid: 10, summaries: (variable: (module: ^0, flags: (linkage: common, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 0))))
 ; Test appending globel variable with reference (tests backward reference on
 ; refs).
 ^12 = gv: (guid: 11, summaries: (variable: (module: ^0, flags: (linkage: appending, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 0), refs: (^4))))
 
 ; Test a referenced global variable.
 ^13 = gv: (guid: 12, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 1))))

 ^26 = typeid: (name: "_ZTS1A", summary: (typeTestRes: (kind: allOnes, sizeM1BitWidth: 7), wpdResolutions: ((offset: 0, wpdRes: (kind: branchFunnel)), (offset: 8, wpdRes: (kind: singleImpl, singleImplName: "_ZN1A1nEi")), (offset: 16, wpdRes: (kind: indir, resByArg: (args: (1, 2), byArg: (kind: indir, byte: 2, bit: 3), args: (3), byArg: (kind: uniformRetVal, info: 1), args: (4), byArg: (kind: uniqueRetVal, info: 1), args: (5), byArg: (kind: virtualConstProp)))))))
 ; Test the other kinds of type test resoultions
 ^27 = typeid: (name: "_ZTS1D", summary: (typeTestRes: (kind: byteArray, sizeM1BitWidth: 0)))
 ^28 = typeid: (name: "_ZTS1E", summary: (typeTestRes: (kind: unsat, sizeM1BitWidth: 0)))
 
 ; Make sure we get back from llvm-dis essentially what we put in via llvm-as.
 ; CHECK: ^0 = module: (path: "thinlto-summary1.o", hash: (1369602428, 2747878711, 259090915, 2507395659, 1141468049))
 ; CHECK: ^1 = module: (path: "thinlto-summary2.o", hash: (2998369023, 4283347029, 1195487472, 2757298015, 1852134156))
-; CHECK: ^2 = gv: (guid: 1, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 10, calls: ((callee: ^15, hotness: hot), (callee: ^17, hotness: cold), (callee: ^16, hotness: none)), refs: (^14, readonly ^13))))
-; CHECK: ^3 = gv: (guid: 2, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 10, calls: ((callee: ^15)))))
-; CHECK: ^4 = gv: (guid: 3, summaries: (function: (module: ^0, flags: (linkage: internal, notEligibleToImport: 0, live: 0, dsoLocal: 1), insts: 1)))
-; CHECK: ^5 = gv: (guid: 4, summaries: (alias: (module: ^0, flags: (linkage: private, notEligibleToImport: 0, live: 0, dsoLocal: 1), aliasee: ^14)))
-; CHECK: ^6 = gv: (guid: 5, summaries: (function: (module: ^0, flags: (linkage: available_externally, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; CHECK: ^7 = gv: (guid: 6, summaries: (function: (module: ^0, flags: (linkage: linkonce, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; CHECK: ^8 = gv: (guid: 7, summaries: (function: (module: ^0, flags: (linkage: linkonce_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; CHECK: ^9 = gv: (guid: 8, summaries: (function: (module: ^0, flags: (linkage: weak_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; CHECK: ^10 = gv: (guid: 9, summaries: (function: (module: ^0, flags: (linkage: weak, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; CHECK: ^11 = gv: (guid: 10, summaries: (variable: (module: ^0, flags: (linkage: common, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 0))))
-; CHECK: ^12 = gv: (guid: 11, summaries: (variable: (module: ^0, flags: (linkage: appending, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 0), refs: (^4))))
-; CHECK: ^13 = gv: (guid: 12, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 1))))
-; CHECK: ^14 = gv: (guid: 13, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1), varFlags: (readonly: 0))))
-; CHECK: ^15 = gv: (guid: 14, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 1, live: 1, dsoLocal: 0), insts: 1)))
-; CHECK: ^16 = gv: (guid: 15, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1, funcFlags: (readNone: 1, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0, noInline: 0))))
-; CHECK: ^17 = gv: (guid: 16, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1, funcFlags: (readNone: 0, readOnly: 1, noRecurse: 0, returnDoesNotAlias: 1, noInline: 0), calls: ((callee: ^15)))))
-; CHECK: ^18 = gv: (guid: 17, summaries: (alias: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1), aliasee: ^14)))
-; CHECK: ^19 = gv: (guid: 18, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 4, typeIdInfo: (typeTests: (^24, ^26)))))
-; CHECK: ^20 = gv: (guid: 19, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 8, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (^27, offset: 16))))))
-; CHECK: ^21 = gv: (guid: 20, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 5, typeIdInfo: (typeCheckedLoadVCalls: (vFuncId: (^25, offset: 16))))))
-; CHECK: ^22 = gv: (guid: 21, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 15, typeIdInfo: (typeTestAssumeConstVCalls: ((vFuncId: (^27, offset: 16), args: (42)), (vFuncId: (^27, offset: 24)))))))
-; CHECK: ^23 = gv: (guid: 22, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 5, typeIdInfo: (typeCheckedLoadConstVCalls: ((vFuncId: (^28, offset: 16), args: (42)))))))
+; CHECK: ^2 = gv: (guid: 1, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 10, calls: ((callee: ^15, hotness: hot), (callee: ^17, hotness: cold), (callee: ^16, hotness: none)), refs: (^14, readonly ^13))))
+; CHECK: ^3 = gv: (guid: 2, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 10, calls: ((callee: ^15)))))
+; CHECK: ^4 = gv: (guid: 3, summaries: (function: (module: ^0, flags: (linkage: internal, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 1)))
+; CHECK: ^5 = gv: (guid: 4, summaries: (alias: (module: ^0, flags: (linkage: private, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), aliasee: ^14)))
+; CHECK: ^6 = gv: (guid: 5, summaries: (function: (module: ^0, flags: (linkage: available_externally, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; CHECK: ^7 = gv: (guid: 6, summaries: (function: (module: ^0, flags: (linkage: linkonce, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; CHECK: ^8 = gv: (guid: 7, summaries: (function: (module: ^0, flags: (linkage: linkonce_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; CHECK: ^9 = gv: (guid: 8, summaries: (function: (module: ^0, flags: (linkage: weak_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 1), insts: 1)))
+; CHECK: ^10 = gv: (guid: 9, summaries: (function: (module: ^0, flags: (linkage: weak, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; CHECK: ^11 = gv: (guid: 10, summaries: (variable: (module: ^0, flags: (linkage: common, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0))))
+; CHECK: ^12 = gv: (guid: 11, summaries: (variable: (module: ^0, flags: (linkage: appending, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 0), refs: (^4))))
+; CHECK: ^13 = gv: (guid: 12, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1))))
+; CHECK: ^14 = gv: (guid: 13, summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), varFlags: (readonly: 0))))
+; CHECK: ^15 = gv: (guid: 14, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 1, live: 1, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; CHECK: ^16 = gv: (guid: 15, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1, funcFlags: (readNone: 1, readOnly: 0, noRecurse: 1, returnDoesNotAlias: 0, noInline: 0))))
+; CHECK: ^17 = gv: (guid: 16, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1, funcFlags: (readNone: 0, readOnly: 1, noRecurse: 0, returnDoesNotAlias: 1, noInline: 0), calls: ((callee: ^15)))))
+; CHECK: ^18 = gv: (guid: 17, summaries: (alias: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), aliasee: ^14)))
+; CHECK: ^19 = gv: (guid: 18, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 4, typeIdInfo: (typeTests: (^24, ^26)))))
+; CHECK: ^20 = gv: (guid: 19, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 8, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (^27, offset: 16))))))
+; CHECK: ^21 = gv: (guid: 20, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 5, typeIdInfo: (typeCheckedLoadVCalls: (vFuncId: (^25, offset: 16))))))
+; CHECK: ^22 = gv: (guid: 21, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 15, typeIdInfo: (typeTestAssumeConstVCalls: ((vFuncId: (^27, offset: 16), args: (42)), (vFuncId: (^27, offset: 24)))))))
+; CHECK: ^23 = gv: (guid: 22, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 5, typeIdInfo: (typeCheckedLoadConstVCalls: ((vFuncId: (^28, offset: 16), args: (42)))))))
 ; CHECK: ^24 = typeid: (name: "_ZTS1C", summary: (typeTestRes: (kind: single, sizeM1BitWidth: 0))) ; guid = 1884921850105019584
 ; CHECK: ^25 = typeid: (name: "_ZTS1B", summary: (typeTestRes: (kind: inline, sizeM1BitWidth: 0, alignLog2: 1, sizeM1: 2, bitMask: 3, inlineBits: 4))) ; guid = 6203814149063363976
 ; CHECK: ^26 = typeid: (name: "_ZTS1A", summary: (typeTestRes: (kind: allOnes, sizeM1BitWidth: 7), wpdResolutions: ((offset: 0, wpdRes: (kind: branchFunnel)), (offset: 8, wpdRes: (kind: singleImpl, singleImplName: "_ZN1A1nEi")), (offset: 16, wpdRes: (kind: indir, resByArg: (args: (1, 2), byArg: (kind: indir, byte: 2, bit: 3), args: (3), byArg: (kind: uniformRetVal, info: 1), args: (4), byArg: (kind: uniqueRetVal, info: 1), args: (5), byArg: (kind: virtualConstProp))))))) ; guid = 7004155349499253778
 ; CHECK: ^27 = typeid: (name: "_ZTS1D", summary: (typeTestRes: (kind: byteArray, sizeM1BitWidth: 0))) ; guid = 9614786172484273522
 ; CHECK: ^28 = typeid: (name: "_ZTS1E", summary: (typeTestRes: (kind: unsat, sizeM1BitWidth: 0))) ; guid = 17437243864166745132

test/Bitcode/thinlto-alias.ll

 entry:
     call void (...) @analias()
     ret i32 0
 }
 
 declare void @analias(...)
 
 ; DIS: ^0 = module: (path: "{{.*}}", hash: (0, 0, 0, 0, 0))
-; DIS: ^1 = gv: (name: "analias", summaries: (alias: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), aliasee: ^2))) ; guid = 12695095382722328222
-; DIS: ^2 = gv: (name: "aliasee", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1))) ; guid = 17407585008595848568
+; DIS: ^1 = gv: (name: "analias", summaries: (alias: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), aliasee: ^2))) ; guid = 12695095382722328222
+; DIS: ^2 = gv: (name: "aliasee", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1))) ; guid = 17407585008595848568
 
 ; COMBINED-DIS: ^0 = module: (path: "{{.*}}thinlto-alias.ll.tmp.o", hash: (0, 0, 0, 0, 0))
 ; COMBINED-DIS: ^1 = module: (path: "{{.*}}thinlto-alias.ll.tmp2.o", hash: (0, 0, 0, 0, 0))
-; COMBINED-DIS: ^2 = gv: (guid: 12695095382722328222, summaries: (alias: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), aliasee: ^4)))
-; COMBINED-DIS: ^3 = gv: (guid: 15822663052811949562, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, calls: ((callee: ^2)))))
-; COMBINED-DIS: ^4 = gv: (guid: 17407585008595848568, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
+; COMBINED-DIS: ^2 = gv: (guid: 12695095382722328222, summaries: (alias: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), aliasee: ^4)))
+; COMBINED-DIS: ^3 = gv: (guid: 15822663052811949562, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, calls: ((callee: ^2)))))
+; COMBINED-DIS: ^4 = gv: (guid: 17407585008595848568, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))

test/Bitcode/thinlto-function-summary-callgraph-profile-summary.ll

 ; DIS: ^1 = gv: (guid: 123)
 ; DIS: ^2 = gv: (name: "none2") ; guid = 3741006263754194003
 ; DIS: ^3 = gv: (name: "hot3") ; guid = 5026609803865204483
 ; DIS: ^4 = gv: (name: "hot2") ; guid = 8117347573235780485
 ; DIS: ^5 = gv: (name: "hot1") ; guid = 9453975128311291976
 ; DIS: ^6 = gv: (name: "cold") ; guid = 11668175513417606517
 ; DIS: ^7 = gv: (name: "hot4") ; guid = 13161834114071272798
 ; DIS: ^8 = gv: (name: "none3") ; guid = 16213681105727317812
-; DIS: ^9 = gv: (name: "hot_function", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 16, calls: ((callee: ^5, hotness: hot), (callee: ^6, hotness: cold), (callee: ^4, hotness: hot), (callee: ^7, hotness: cold), (callee: ^10, hotness: none), (callee: ^3, hotness: hot), (callee: ^2, hotness: none), (callee: ^8, hotness: none), (callee: ^1, hotness: critical))))) ; guid = 17381606045411660303
+; DIS: ^9 = gv: (name: "hot_function", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 16, calls: ((callee: ^5, hotness: hot), (callee: ^6, hotness: cold), (callee: ^4, hotness: hot), (callee: ^7, hotness: cold), (callee: ^10, hotness: none), (callee: ^3, hotness: hot), (callee: ^2, hotness: none), (callee: ^8, hotness: none), (callee: ^1, hotness: critical))))) ; guid = 17381606045411660303
 ; DIS: ^10 = gv: (name: "none1") ; guid = 17712061229457633252
 
 ; COMBINED-DIS: ^0 = module: (path: "{{.*}}thinlto-function-summary-callgraph-profile-summary.ll.tmp.o", hash: (0, 0, 0, 0, 0))
 ; COMBINED-DIS: ^1 = module: (path: "{{.*}}thinlto-function-summary-callgraph-profile-summary.ll.tmp2.o", hash: (0, 0, 0, 0, 0))
-; COMBINED-DIS: ^2 = gv: (guid: 3741006263754194003, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; COMBINED-DIS: ^3 = gv: (guid: 5026609803865204483, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; COMBINED-DIS: ^4 = gv: (guid: 8117347573235780485, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; COMBINED-DIS: ^5 = gv: (guid: 9453975128311291976, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; COMBINED-DIS: ^6 = gv: (guid: 11668175513417606517, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; COMBINED-DIS: ^7 = gv: (guid: 16213681105727317812, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
-; COMBINED-DIS: ^8 = gv: (guid: 17381606045411660303, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 16, calls: ((callee: ^5, hotness: hot), (callee: ^6, hotness: cold), (callee: ^4, hotness: hot), (callee: ^9, hotness: none), (callee: ^3, hotness: hot), (callee: ^2, hotness: none), (callee: ^7, hotness: none)))))
-; COMBINED-DIS: ^9 = gv: (guid: 17712061229457633252, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 1)))
+; COMBINED-DIS: ^2 = gv: (guid: 3741006263754194003, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; COMBINED-DIS: ^3 = gv: (guid: 5026609803865204483, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; COMBINED-DIS: ^4 = gv: (guid: 8117347573235780485, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; COMBINED-DIS: ^5 = gv: (guid: 9453975128311291976, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; COMBINED-DIS: ^6 = gv: (guid: 11668175513417606517, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; COMBINED-DIS: ^7 = gv: (guid: 16213681105727317812, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; COMBINED-DIS: ^8 = gv: (guid: 17381606045411660303, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 16, calls: ((callee: ^5, hotness: hot), (callee: ^6, hotness: cold), (callee: ^4, hotness: hot), (callee: ^9, hotness: none), (callee: ^3, hotness: hot), (callee: ^2, hotness: none), (callee: ^7, hotness: none)))))
+; COMBINED-DIS: ^9 = gv: (guid: 17712061229457633252, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 1)))

test/Bitcode/thinlto-function-summary-callgraph-relbf.ll

 
 declare void @func(...) #1
 @undefinedglob = external global i32
 
 ; OLD: Index {{.*}} contains 1 nodes (1 functions, 0 alias, 0 globals) and 1 edges (0 refs and 1 calls)
 
 ; DIS: ^0 = module: (path: "{{.*}}", hash: (0, 0, 0, 0, 0))
 ; DIS: ^1 = gv: (name: "func") ; guid = 7289175272376759421
-; DIS: ^2 = gv: (name: "main", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 3, calls: ((callee: ^1, relbf: 256)), refs: (readonly ^3)))) ; guid = 15822663052811949562
+; DIS: ^2 = gv: (name: "main", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 3, calls: ((callee: ^1, relbf: 256)), refs: (readonly ^3)))) ; guid = 15822663052811949562
 ; DIS: ^3 = gv: (name: "undefinedglob") ; guid = 18036901804029949403

test/Bitcode/thinlto-function-summary-refgraph.ll

entry:
   call i8  @llvm.ctpop.i8( i8 10 )
   ret i32 0
 }
 
 ; Don't try to match summary IDs. The numbering depends on the map iteration
 ; order, which depends on GUID, and the private function Y GUID will depend
 ; on the path to the test.
 ; DIS: ^0 = module: (path: "{{.*}}", hash: (0, 0, 0, 0, 0))
-; DIS-DAG: = gv: (name: "Z", summaries: (function: (module: ^0, flags: (linkage: linkonce_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, calls: ((callee: ^{{.*}}))))) ; guid = 104084381700047393
-; DIS-DAG: = gv: (name: "X", summaries: (function: (module: ^0, flags: (linkage: available_externally, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, calls: ((callee: ^{{.*}})), refs: (^{{.*}})))) ; guid = 1881667236089500162
-; DIS-DAG: = gv: (name: "W", summaries: (function: (module: ^0, flags: (linkage: weak_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, calls: ((callee: ^{{.*}})), refs: (^{{.*}})))) ; guid = 5790125716599269729
+; DIS-DAG: = gv: (name: "Z", summaries: (function: (module: ^0, flags: (linkage: linkonce_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, calls: ((callee: ^{{.*}}))))) ; guid = 104084381700047393
+; DIS-DAG: = gv: (name: "X", summaries: (function: (module: ^0, flags: (linkage: available_externally, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, calls: ((callee: ^{{.*}})), refs: (^{{.*}})))) ; guid = 1881667236089500162
+; DIS-DAG: = gv: (name: "W", summaries: (function: (module: ^0, flags: (linkage: weak_odr, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, calls: ((callee: ^{{.*}})), refs: (^{{.*}})))) ; guid = 5790125716599269729
 ; DIS-DAG: = gv: (name: "foo") ; guid = 6699318081062747564
 ; DIS-DAG: = gv: (name: "func") ; guid = 7289175272376759421
 ; DIS-DAG: = gv: (name: "func3") ; guid = 11517462787082255043
-; DIS-DAG: = gv: (name: "globalvar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 1)))) ; guid = 12887606300320728018
+; DIS-DAG: = gv: (name: "globalvar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1)))) ; guid = 12887606300320728018
 ; DIS-DAG: = gv: (name: "func2") ; guid = 14069196320850861797
 ; DIS-DAG: = gv: (name: "llvm.ctpop.i8") ; guid = 15254915475081819833
-; DIS-DAG: = gv: (name: "main", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 9, calls: ((callee: ^{{.*}})), refs: (^{{.*}})))) ; guid = 15822663052811949562
-; DIS-DAG: = gv: (name: "bar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), varFlags: (readonly: 1),  refs: (^{{.*}})))) ; guid = 16434608426314478903
+; DIS-DAG: = gv: (name: "main", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 9, calls: ((callee: ^{{.*}})), refs: (^{{.*}})))) ; guid = 15822663052811949562
+; DIS-DAG: = gv: (name: "bar", summaries: (variable: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), varFlags: (readonly: 1),  refs: (^{{.*}})))) ; guid = 16434608426314478903
 ; Don't try to match the exact GUID. Since it is private, the file path
 ; will get hashed, and that will be test dependent.
-; DIS-DAG: = gv: (name: "Y", summaries: (function: (module: ^0, flags: (linkage: private, notEligibleToImport: 0, live: 0, dsoLocal: 1), insts: 14, calls: ((callee: ^{{.*}}))))) ; guid =
+; DIS-DAG: = gv: (name: "Y", summaries: (function: (module: ^0, flags: (linkage: private, notEligibleToImport: 0, live: 0, dsoLocal: 1, canAutoHide: 0), insts: 14, calls: ((callee: ^{{.*}}))))) ; guid =

test/Bitcode/thinlto-type-tests.ll

define i1 @h() {
   %p = call i1 @llvm.type.test(i8* null, metadata !"bar")
   ret i1 %p
 }
 
 declare i1 @llvm.type.test(i8*, metadata) nounwind readnone
 
 ; DIS: ^0 = module: (path: "{{.*}}", hash: (0, 0, 0, 0, 0))
 ; DIS: ^1 = gv: (name: "llvm.type.test") ; guid = 608142985856744218
-; DIS: ^2 = gv: (name: "h", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, typeIdInfo: (typeTests: (16434608426314478903))))) ; guid = 8124147457056772133
-; DIS: ^3 = gv: (name: "g", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 4, typeIdInfo: (typeTests: (6699318081062747564, 16434608426314478903))))) ; guid = 13146401226427987378
-; DIS: ^4 = gv: (name: "f", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, typeIdInfo: (typeTests: (6699318081062747564))))) ; guid = 14740650423002898831
+; DIS: ^2 = gv: (name: "h", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, typeIdInfo: (typeTests: (16434608426314478903))))) ; guid = 8124147457056772133
+; DIS: ^3 = gv: (name: "g", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 4, typeIdInfo: (typeTests: (6699318081062747564, 16434608426314478903))))) ; guid = 13146401226427987378
+; DIS: ^4 = gv: (name: "f", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, typeIdInfo: (typeTests: (6699318081062747564))))) ; guid = 14740650423002898831
 
 ; COMBINED-DIS: ^0 = module: (path: "{{.*}}thinlto-type-tests.ll.tmp.o", hash: (0, 0, 0, 0, 0))
-; COMBINED-DIS: ^1 = gv: (guid: 8124147457056772133, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, typeIdInfo: (typeTests: (16434608426314478903)))))
-; COMBINED-DIS: ^2 = gv: (guid: 13146401226427987378, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 4, typeIdInfo: (typeTests: (6699318081062747564, 16434608426314478903)))))
-; COMBINED-DIS: ^3 = gv: (guid: 14740650423002898831, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, typeIdInfo: (typeTests: (6699318081062747564)))))
+; COMBINED-DIS: ^1 = gv: (guid: 8124147457056772133, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, typeIdInfo: (typeTests: (16434608426314478903)))))
+; COMBINED-DIS: ^2 = gv: (guid: 13146401226427987378, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 4, typeIdInfo: (typeTests: (6699318081062747564, 16434608426314478903)))))
+; COMBINED-DIS: ^3 = gv: (guid: 14740650423002898831, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, typeIdInfo: (typeTests: (6699318081062747564)))))

test/Bitcode/thinlto-type-vcalls.ll

 }
 
 declare i1 @llvm.type.test(i8*, metadata) nounwind readnone
 declare void @llvm.assume(i1)
 declare {i8*, i1} @llvm.type.checked.load(i8*, i32, metadata)
 
 ; DIS: ^0 = module: (path: "{{.*}}", hash: (0, 0, 0, 0, 0))
 ; DIS: ^1 = gv: (name: "llvm.type.test") ; guid = 608142985856744218
-; DIS: ^2 = gv: (name: "f1", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 8, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16)))))) ; guid = 2072045998141807037
-; DIS: ^3 = gv: (name: "f3", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 5, typeIdInfo: (typeCheckedLoadVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16)))))) ; guid = 4197650231481825559
+; DIS: ^2 = gv: (name: "f1", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 8, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16)))))) ; guid = 2072045998141807037
+; DIS: ^3 = gv: (name: "f3", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 5, typeIdInfo: (typeCheckedLoadVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16)))))) ; guid = 4197650231481825559
 ; DIS: ^4 = gv: (name: "llvm.type.checked.load") ; guid = 5568222536364573403
 ; DIS: ^5 = gv: (name: "llvm.assume") ; guid = 6385187066495850096
-; DIS: ^6 = gv: (name: "f2", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 15, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 24), vFuncId: (guid: 16434608426314478903, offset: 32)))))) ; guid = 8471399308421654326
-; DIS: ^7 = gv: (name: "f4", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 15, typeIdInfo: (typeTestAssumeConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42)), (vFuncId: (guid: 6699318081062747564, offset: 24), args: (43))))))) ; guid = 10064745020953272174
-; DIS: ^8 = gv: (name: "f5", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 5, typeIdInfo: (typeCheckedLoadConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42))))))) ; guid = 11686717102184386164
-; DIS: ^9 = gv: (name: "f6", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, typeIdInfo: (typeTests: (7546896869197086323))))) ; guid = 11834966808443348068
+; DIS: ^6 = gv: (name: "f2", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 15, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 24), vFuncId: (guid: 16434608426314478903, offset: 32)))))) ; guid = 8471399308421654326
+; DIS: ^7 = gv: (name: "f4", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 15, typeIdInfo: (typeTestAssumeConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42)), (vFuncId: (guid: 6699318081062747564, offset: 24), args: (43))))))) ; guid = 10064745020953272174
+; DIS: ^8 = gv: (name: "f5", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 5, typeIdInfo: (typeCheckedLoadConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42))))))) ; guid = 11686717102184386164
+; DIS: ^9 = gv: (name: "f6", summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, typeIdInfo: (typeTests: (7546896869197086323))))) ; guid = 11834966808443348068
 
 ; COMBINED-DIS: ^0 = module: (path: "{{.*}}thinlto-type-vcalls.ll.tmp.o", hash: (0, 0, 0, 0, 0))
-; COMBINED-DIS: ^1 = gv: (guid: 2072045998141807037, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 8, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16))))))
-; COMBINED-DIS: ^2 = gv: (guid: 4197650231481825559, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 5, typeIdInfo: (typeCheckedLoadVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16))))))
-; COMBINED-DIS: ^3 = gv: (guid: 8471399308421654326, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 15, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 24), vFuncId: (guid: 16434608426314478903, offset: 32))))))
-; COMBINED-DIS: ^4 = gv: (guid: 10064745020953272174, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 15, typeIdInfo: (typeTestAssumeConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42)), (vFuncId: (guid: 6699318081062747564, offset: 24), args: (43)))))))
-; COMBINED-DIS: ^5 = gv: (guid: 11686717102184386164, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 5, typeIdInfo: (typeCheckedLoadConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42)))))))
-; COMBINED-DIS: ^6 = gv: (guid: 11834966808443348068, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0), insts: 2, typeIdInfo: (typeTests: (7546896869197086323)))))
+; COMBINED-DIS: ^1 = gv: (guid: 2072045998141807037, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 8, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16))))))
+; COMBINED-DIS: ^2 = gv: (guid: 4197650231481825559, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 5, typeIdInfo: (typeCheckedLoadVCalls: (vFuncId: (guid: 6699318081062747564, offset: 16))))))
+; COMBINED-DIS: ^3 = gv: (guid: 8471399308421654326, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 15, typeIdInfo: (typeTestAssumeVCalls: (vFuncId: (guid: 6699318081062747564, offset: 24), vFuncId: (guid: 16434608426314478903, offset: 32))))))
+; COMBINED-DIS: ^4 = gv: (guid: 10064745020953272174, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 15, typeIdInfo: (typeTestAssumeConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42)), (vFuncId: (guid: 6699318081062747564, offset: 24), args: (43)))))))
+; COMBINED-DIS: ^5 = gv: (guid: 11686717102184386164, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 5, typeIdInfo: (typeCheckedLoadConstVCalls: ((vFuncId: (guid: 6699318081062747564, offset: 16), args: (42)))))))
+; COMBINED-DIS: ^6 = gv: (guid: 11834966808443348068, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 0, dsoLocal: 0, canAutoHide: 0), insts: 2, typeIdInfo: (typeTests: (7546896869197086323)))))

test/ThinLTO/X86/Inputs/linkonce_odr_unnamed_addr.ll

+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+@linkonceodrunnamed = linkonce_odr unnamed_addr constant i32 0
+@odrunnamed = weak_odr unnamed_addr constant i32 0

test/ThinLTO/X86/linkonce_odr_unnamed_addr.ll

 ; This test ensures that when linkonce_odr + unnamed_addr symbols promoted to
-; weak symbols, it preserves the auto hide property.
+; weak symbols, it preserves the auto hide property when possible.
 
 ; RUN: opt -module-summary %s -o %t.bc
-; RUN: opt -module-summary %s -o %t2.bc
+; RUN: opt -module-summary %p/Inputs/linkonce_odr_unnamed_addr.ll -o %t2.bc
+; Check old LTO API
 ; RUN: llvm-lto -thinlto-action=thinlink -o %t3.bc %t.bc %t2.bc
 ; RUN: llvm-lto -thinlto-action=promote %t.bc -thinlto-index=%t3.bc -o - | llvm-dis -o - | FileCheck %s
+; Check new LTO API
+; RUN: llvm-lto2 run -save-temps -o %t6.bc %t.bc %t2.bc -r=%t.bc,linkonceodrunnamed,p -r=%t.bc,odrunnamed,p -r=%t2.bc,linkonceodrunnamed, -r=%t2.bc,odrunnamed,
+; RUN: llvm-dis %t6.bc.1.1.promote.bc -o - | FileCheck %s
 
+; Now test when one module does not have a summary. In that case we must be
+; conservative and not auto hide.
+; RUN: opt %p/Inputs/linkonce_odr_unnamed_addr.ll -o %t4.bc
+; Check new LTO API (old LTO API does not detect this case).
+; RUN: llvm-lto2 run -save-temps -o %t6.bc %t.bc %t4.bc -r=%t.bc,linkonceodrunnamed,p -r=%t.bc,odrunnamed,p -r=%t4.bc,linkonceodrunnamed, -r=%t4.bc,odrunnamed,
+; RUN: llvm-dis %t6.bc.1.1.promote.bc -o - | FileCheck %s --check-prefix=NOSUMMARY
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+; In this case all copies are linkonce_odr, so it may be hidden.
 ; CHECK: @linkonceodrunnamed = weak_odr hidden unnamed_addr constant i32 0
+; NOSUMMARY: @linkonceodrunnamed = weak_odr unnamed_addr constant i32 0
 @linkonceodrunnamed = linkonce_odr unnamed_addr constant i32 0
+
+; In this case, the other copy was weak_odr, so it may not be hidden.
+; CHECK: @odrunnamed = weak_odr unnamed_addr constant i32 0
+; NOSUMMARY: @odrunnamed = weak_odr unnamed_addr constant i32 0
+@odrunnamed = linkonce_odr unnamed_addr constant i32 0

test/ThinLTO/X86/linkonce_resolution_comdat.ll

 ; This test ensures that we drop the preempted copy of @f from %t2.bc from its
 ; comdat after making it available_externally. If not we would get a
 ; verification error.
 ; RUN: opt -module-summary %s -o %t1.bc
 ; RUN: opt -module-summary %p/Inputs/linkonce_resolution_comdat.ll -o %t2.bc
 ; RUN: llvm-lto -thinlto-action=run %t1.bc %t2.bc -exported-symbol=f -exported-symbol=g -thinlto-save-temps=%t3.
 
 ; RUN: llvm-dis %t3.0.3.imported.bc -o - | FileCheck %s --check-prefix=IMPORT1
 ; RUN: llvm-dis %t3.1.3.imported.bc -o - | FileCheck %s --check-prefix=IMPORT2
 ; Copy from first module is prevailing and converted to weak_odr, copy
 ; from second module is preempted and converted to available_externally and
 ; removed from comdat.
-; IMPORT1: define weak_odr hidden i32 @f(i8*) unnamed_addr comdat($c1) {
+; IMPORT1: define weak_odr i32 @f(i8*) unnamed_addr comdat($c1) {
 ; IMPORT2: define available_externally i32 @f(i8*) unnamed_addr {
 
 ; RUN: llvm-nm -o - < %t1.bc.thinlto.o | FileCheck %s --check-prefix=NM1
 ; NM1: W f
 
 ; RUN: llvm-nm -o - < %t2.bc.thinlto.o | FileCheck %s --check-prefix=NM2
 ; f() would have been turned into available_externally since it is preempted,
 ; and inlined into g()

test/Transforms/LowerTypeTests/import-unsat.ll

 ; Test that we correctly import an unsat resolution for type identifier "typeid1".
 ; RUN: opt -S -lowertypetests -lowertypetests-summary-action=import -lowertypetests-read-summary=%S/Inputs/import-unsat.yaml -lowertypetests-write-summary=%t < %s | FileCheck %s
 ; RUN: FileCheck --check-prefix=SUMMARY %s < %t
 
 ; SUMMARY:      GlobalValueMap:
 ; SUMMARY-NEXT:   42:
 ; SUMMARY-NEXT:    - Linkage:             0
 ; SUMMARY-NEXT:      NotEligibleToImport: false
 ; SUMMARY-NEXT:      Live:                true
 ; SUMMARY-NEXT:      Local:               false
+; SUMMARY-NEXT:      CanAutoHide:         false
 ; SUMMARY-NEXT:      TypeTests: [ 123 ]
 ; SUMMARY-NEXT: TypeIdMap:
 ; SUMMARY-NEXT:   typeid1:
 ; SUMMARY-NEXT:     TTRes:
 ; SUMMARY-NEXT:       Kind:            Unsat
 ; SUMMARY-NEXT:       SizeM1BitWidth:  0
 
 target datalayout = "e-p:32:32"
 
 declare i1 @llvm.type.test(i8* %ptr, metadata %bitset) nounwind readnone
 
 define i1 @foo(i8* %p) {
   %x = call i1 @llvm.type.test(i8* %p, metadata !"typeid1")
   ; CHECK: ret i1 false
   ret i1 %x
 }

test/Transforms/WholeProgramDevirt/import-indir.ll

 ; Test that we correctly import an indir resolution for type identifier "typeid1".
 ; RUN: opt -S -wholeprogramdevirt -wholeprogramdevirt-summary-action=import -wholeprogramdevirt-read-summary=%S/Inputs/import-indir.yaml -wholeprogramdevirt-write-summary=%t < %s | FileCheck %s
 ; RUN: FileCheck --check-prefix=SUMMARY %s < %t
 
 ; SUMMARY:     GlobalValueMap:
 ; SUMMARY-NEXT:  42:
 ; SUMMARY-NEXT:    - Linkage:             0
 ; SUMMARY-NEXT:      NotEligibleToImport: false
 ; SUMMARY-NEXT:      Live:                true
 ; SUMMARY-NEXT:      Local:               false
+; SUMMARY-NEXT:      CanAutoHide:         false
 ; SUMMARY-NEXT:      TypeTestAssumeVCalls:
 ; SUMMARY-NEXT:        - GUID:            123
 ; SUMMARY-NEXT:          Offset:          0
 ; SUMMARY-NEXT:        - GUID:            456
 ; SUMMARY-NEXT:          Offset:          4
 ; SUMMARY-NEXT:      TypeCheckedLoadVCalls:
 ; SUMMARY-NEXT:        - GUID:            789
 ; SUMMARY-NEXT:          Offset:          8

test/tools/gold/X86/thinlto.ll

 ; BACKEND2-NEXT: <VERSION
 ; BACKEND2-NEXT: <FLAGS
 ; BACKEND2-NEXT: <VALUE_GUID op0=1 op1=-5300342847281564238
 ; BACKEND2-NEXT: <COMBINED
 ; BACKEND2-NEXT: </GLOBALVAL_SUMMARY_BLOCK
 
 ; DIS1: ^0 = module: (path: "{{.*}}thinlto.ll.tmp.o", hash: (0, 0, 0, 0, 0))
 ; DIS1: ^1 = module: (path: "{{.*}}thinlto.ll.tmp2.o", hash: (0, 0, 0, 0, 0))
-; DIS1: ^2 = gv: (guid: 13146401226427987378, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 1, dsoLocal: 0), insts: 1)))
-; DIS1: ^3 = gv: (guid: 14740650423002898831, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 1, dsoLocal: 0), insts: 2, calls: ((callee: ^2)))))
+; DIS1: ^2 = gv: (guid: 13146401226427987378, summaries: (function: (module: ^1, flags: (linkage: external, notEligibleToImport: 0, live: 1, dsoLocal: 0, canAutoHide: 0), insts: 1)))
+; DIS1: ^3 = gv: (guid: 14740650423002898831, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 1, dsoLocal: 0, canAutoHide: 0), insts: 2, calls: ((callee: ^2)))))
 
 ; DIS2: ^0 = module: (path: "{{.*}}thinlto.ll.tmp2.o", hash: (0, 0, 0, 0, 0))
-; DIS2: ^1 = gv: (guid: 13146401226427987378, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 1, dsoLocal: 0), insts: 1)))
+; DIS2: ^1 = gv: (guid: 13146401226427987378, summaries: (function: (module: ^0, flags: (linkage: external, notEligibleToImport: 0, live: 1, dsoLocal: 0, canAutoHide: 0), insts: 1)))
 
 ; COMBINED: <MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <ENTRY {{.*}} record string = '{{.*}}/test/tools/gold/X86/Output/thinlto.ll.tmp{{.*}}.o'
 ; COMBINED-NEXT: <ENTRY {{.*}} record string = '{{.*}}/test/tools/gold/X86/Output/thinlto.ll.tmp{{.*}}.o'
 ; COMBINED-NEXT: </MODULE_STRTAB_BLOCK
 ; COMBINED-NEXT: <GLOBALVAL_SUMMARY_BLOCK
 ; COMBINED-NEXT: <VERSION
 ; COMBINED-NEXT: <FLAGS