2 files changed, 26 insertions, 8 deletions
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 47388c2..105edb9 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -8164,6 +8164,14 @@ Error ModuleSummaryIndexBitcodeReader::parseEntireSummary(unsigned ID) {
           ContextSizes.reserve(NumContextSizeInfoEntries);
           for (unsigned J = 0; J < NumContextSizeInfoEntries; J++) {
             assert(ContextIdIndex < PendingContextIds.size());
+            // Skip any 0 entries for MIBs without the context size info.
+            if (PendingContextIds[ContextIdIndex] == 0) {
+              // The size should also be 0 if the context was 0.
+              assert(!Record[I]);
+              ContextIdIndex++;
+              I++;
+              continue;
+            }
             // PendingContextIds read from the preceding FS_ALLOC_CONTEXT_IDS
             // should be in the same order as the total sizes.
             ContextSizes.push_back(
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
index 8789b31..fad8ebf 100644
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -23,6 +23,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/MemoryProfileInfo.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/Bitcode/BitcodeCommon.h"
 #include "llvm/Bitcode/BitcodeReader.h"
@@ -4585,14 +4586,23 @@ void ModuleBitcodeWriterBase::writePerModuleGlobalValueSummary() {
     Stream.EmitRecord(bitc::FS_STACK_IDS, Vals, StackIdAbbvId);
   }
 
-  // n x context id
-  auto ContextIdAbbv = std::make_shared<BitCodeAbbrev>();
-  ContextIdAbbv->Add(BitCodeAbbrevOp(bitc::FS_ALLOC_CONTEXT_IDS));
-  ContextIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
-  // The context ids are hashes that are close to 64 bits in size, so emitting
-  // as a pair of 32-bit fixed-width values is more efficient than a VBR.
-  ContextIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
-  unsigned ContextIdAbbvId = Stream.EmitAbbrev(std::move(ContextIdAbbv));
+  unsigned ContextIdAbbvId = 0;
+  if (metadataMayIncludeContextSizeInfo()) {
+    // n x context id
+    auto ContextIdAbbv = std::make_shared<BitCodeAbbrev>();
+    ContextIdAbbv->Add(BitCodeAbbrevOp(bitc::FS_ALLOC_CONTEXT_IDS));
+    ContextIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Array));
+    // The context ids are hashes that are close to 64 bits in size, so emitting
+    // as a pair of 32-bit fixed-width values is more efficient than a VBR if we
+    // are emitting them for all MIBs. Otherwise we use VBR to better compress 0
+    // values that are expected to more frequently occur in an alloc's memprof
+    // summary.
+    if (metadataIncludesAllContextSizeInfo())
+      ContextIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 32));
+    else
+      ContextIdAbbv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 8));
+    ContextIdAbbvId = Stream.EmitAbbrev(std::move(ContextIdAbbv));
+  }
 
   // Abbrev for FS_PERMODULE_PROFILE.
   Abbv = std::make_shared<BitCodeAbbrev>();