[ThinLTO] Use valueid instead of bitcode offsets in combined index file

Summary:
With the removal of support for lazy parsing of combined index summary
records (e.g. r267344), we no longer need to include the summary record
bitcode offset in the VST entries for definitions. Change the combined
index format to be similar to the per-module index format in using value
ids to cross-reference from the summary record to the VST entry (rather
than the summary record bitcode offset to cross-reference in the other
direction).

The visible changes are:
1) Add the value id to the combined summary records
2) Remove the summary offset from the combined VST records, which has
the following effects:
- No longer need the VST_CODE_COMBINED_GVDEFENTRY record, as all
  combined index VST entries now only contain the value id and
  corresponding GUID.
- No longer have duplicate VST entries in the case where there are
  multiple definitions of a symbol (e.g. weak/linkonce), as they all
  have the same value id and GUID.

An implication of #2 above is that in order to hook up an alias to the
correct aliasee based on the value id of the aliasee recorded in the
combined index alias record, we need to scan the entries in the index
for that GUID to find the one from the same module (i.e. the case where
there are multiple entries for the aliasee). But the reader no longer
has to maintain a special map to hook up the alias/aliasee.

Reviewers: joker.eph

Subscribers: joker.eph, llvm-commits

Differential Revision: http://reviews.llvm.org/D19481

llvm-svn: 267712

1 files changed, 23 insertions, 61 deletions

diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index c68a2929dbe..6764e779e0a 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -270,10 +270,6 @@ class IndexBitcodeWriter : public BitcodeWriter {
   /// Tracks the last value id recorded in the GUIDToValueMap.
   unsigned GlobalValueId = 0;
 
-  /// Record the starting offset of each summary entry for use in the VST
-  /// entry, and for any possible alias.
-  DenseMap<const GlobalValueSummary *, uint64_t> SummaryToOffsetMap;
-
 public:
   /// Constructs a IndexBitcodeWriter object for the given combined index,
   /// writing to the provided \p Buffer.
@@ -312,13 +308,6 @@ private:
       return VMI->second;
     }
   }
-  unsigned popValueId(GlobalValue::GUID ValGUID) {
-    const auto &VMI = GUIDToValueIdMap.find(ValGUID);
-    assert(VMI != GUIDToValueIdMap.end());
-    unsigned ValueId = VMI->second;
-    GUIDToValueIdMap.erase(VMI);
-    return ValueId;
-  }
   std::map<GlobalValue::GUID, unsigned> &valueIds() { return GUIDToValueIdMap; }
 };
 
@@ -2629,38 +2618,12 @@ void IndexBitcodeWriter::writeCombinedValueSymbolTable() {
   Stream.EnterSubblock(bitc::VALUE_SYMTAB_BLOCK_ID, 4);
 
   BitCodeAbbrev *Abbv = new BitCodeAbbrev();
-  Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_COMBINED_GVDEFENTRY));
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // sumoffset
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // guid
-  unsigned DefEntryAbbrev = Stream.EmitAbbrev(Abbv);
-
-  Abbv = new BitCodeAbbrev();
   Abbv->Add(BitCodeAbbrevOp(bitc::VST_CODE_COMBINED_ENTRY));
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // valueid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8)); // refguid
   unsigned EntryAbbrev = Stream.EmitAbbrev(Abbv);
 
   SmallVector<uint64_t, 64> NameVals;
-
-  for (const auto &GSI : Index) {
-    GlobalValue::GUID ValGUID = GSI.first;
-    unsigned ValueId = popValueId(ValGUID);
-
-    for (const auto &SI : GSI.second) {
-      // VST_CODE_COMBINED_GVDEFENTRY: [valueid, sumoffset, guid]
-      NameVals.push_back(ValueId);
-      auto Offset = SummaryToOffsetMap[SI.get()];
-      assert(Offset);
-      NameVals.push_back(Offset);
-      NameVals.push_back(ValGUID);
-
-      // Emit the finished record.
-      Stream.EmitRecord(bitc::VST_CODE_COMBINED_GVDEFENTRY, NameVals,
-                        DefEntryAbbrev);
-      NameVals.clear();
-    }
-  }
   for (const auto &GVI : valueIds()) {
     // VST_CODE_COMBINED_ENTRY: [valueid, refguid]
     NameVals.push_back(GVI.second);
@@ -3194,6 +3157,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   // Abbrev for FS_COMBINED.
   BitCodeAbbrev *Abbv = new BitCodeAbbrev();
   Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
@@ -3206,6 +3170,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   // Abbrev for FS_COMBINED_PROFILE.
   Abbv = new BitCodeAbbrev();
   Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_PROFILE));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // instcount
@@ -3218,6 +3183,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   // Abbrev for FS_COMBINED_GLOBALVAR_INIT_REFS.
   Abbv = new BitCodeAbbrev();
   Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_GLOBALVAR_INIT_REFS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));    // valueids
@@ -3227,15 +3193,19 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   // Abbrev for FS_COMBINED_ALIAS.
   Abbv = new BitCodeAbbrev();
   Abbv->Add(BitCodeAbbrevOp(bitc::FS_COMBINED_ALIAS));
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // modid
   Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 6));   // flags
-  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // offset
+  Abbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));   // valueid
   unsigned FSAliasAbbrev = Stream.EmitAbbrev(Abbv);
 
-  // The aliases are emitted as a post-pass, and will point to the summary
-  // offset id of the aliasee. Save them in a vector for post-processing.
+  // The aliases are emitted as a post-pass, and will point to the value
+  // id of the aliasee. Save them in a vector for post-processing.
   SmallVector<AliasSummary *, 64> Aliases;
 
+  // Save the value id for each summary for alias emission.
+  DenseMap<const GlobalValueSummary *, unsigned> SummaryToValueIdMap;
+
   SmallVector<uint64_t, 64> NameVals;
 
   // For local linkage, we also emit the original name separately
@@ -3252,6 +3222,11 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
     for (auto &SI : GSI.second) {
       GlobalValueSummary *S = SI.get();
       assert(S);
+
+      assert(hasValueId(GSI.first));
+      unsigned ValueId = getValueId(GSI.first);
+      SummaryToValueIdMap[S] = ValueId;
+
       if (auto *AS = dyn_cast<AliasSummary>(S)) {
         // Will process aliases as a post-pass because the reader wants all
         // global to be loaded first.
@@ -3260,18 +3235,13 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
       }
 
       if (auto *VS = dyn_cast<GlobalVarSummary>(S)) {
+        NameVals.push_back(ValueId);
         NameVals.push_back(Index.getModuleId(VS->modulePath()));
         NameVals.push_back(getEncodedGVSummaryFlags(VS->flags()));
         for (auto &RI : VS->refs()) {
           NameVals.push_back(getValueId(RI.getGUID()));
         }
 
-        // Record the starting offset of this summary entry for use in the VST
-        // entry, and for any possible alias. Add the current code size since
-        // the reader will invoke readRecord after the abbrev id read.
-        SummaryToOffsetMap[S] =
-            Stream.GetCurrentBitNo() + Stream.GetAbbrevIDWidth();
-
         // Emit the finished record.
         Stream.EmitRecord(bitc::FS_COMBINED_GLOBALVAR_INIT_REFS, NameVals,
                           FSModRefsAbbrev);
@@ -3281,6 +3251,7 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
       }
 
       auto *FS = cast<FunctionSummary>(S);
+      NameVals.push_back(ValueId);
       NameVals.push_back(Index.getModuleId(FS->modulePath()));
       NameVals.push_back(getEncodedGVSummaryFlags(FS->flags()));
       NameVals.push_back(FS->instCount());
@@ -3309,12 +3280,6 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
           NameVals.push_back(EI.second.ProfileCount);
       }
 
-      // Record the starting offset of this summary entry for use in the VST
-      // entry, and for any possible alias. Add the current code size since
-      // the reader will invoke readRecord after the abbrev id read.
-      SummaryToOffsetMap[S] =
-          Stream.GetCurrentBitNo() + Stream.GetAbbrevIDWidth();
-
       unsigned FSAbbrev =
           (HasProfileData ? FSCallsProfileAbbrev : FSCallsAbbrev);
       unsigned Code =
@@ -3328,17 +3293,14 @@ void IndexBitcodeWriter::writeCombinedGlobalValueSummary() {
   }
 
   for (auto *AS : Aliases) {
+    auto AliasValueId = SummaryToValueIdMap[AS];
+    assert(AliasValueId);
+    NameVals.push_back(AliasValueId);
     NameVals.push_back(Index.getModuleId(AS->modulePath()));
     NameVals.push_back(getEncodedGVSummaryFlags(AS->flags()));
-    auto AliaseeOffset = SummaryToOffsetMap[&AS->getAliasee()];
-    assert(AliaseeOffset);
-    NameVals.push_back(AliaseeOffset);
-
-    // Record the starting offset of this summary entry for use
-    // in the VST entry. Add the current code size since the
-    // reader will invoke readRecord after the abbrev id read.
-    SummaryToOffsetMap[AS] =
-        Stream.GetCurrentBitNo() + Stream.GetAbbrevIDWidth();
+    auto AliaseeValueId = SummaryToValueIdMap[&AS->getAliasee()];
+    assert(AliaseeValueId);
+    NameVals.push_back(AliaseeValueId);
 
     // Emit the finished record.
     Stream.EmitRecord(bitc::FS_COMBINED_ALIAS, NameVals, FSAliasAbbrev);