Implement a safer bitcode upgrade for DISubprogram.

The bitcode upgrade I added for DISubprogram in r266446 was based on the
assumption that the CU node for the subprogram was already materialized by the
time the DISubprogram is visited. This assumption may not hold true as future
versions of LLVM may decide to write out bitcode in a different order. This
patch corrects this by introducing a versioning bit next to the distinct flag to
unambiguously differentiate the new from the old record layouts.

Note for people stabilizing LLVM out-of-tree: This patch introduces a bitcode
incompatibility with llvm trunk revisions from r266446 — this commit. (But
D19987 will ensure that it degrades gracefully).

http://reviews.llvm.org/D20004
rdar://problem/26074194

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268816 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 11ddd0135169e92957ff76fde147746f9ddee903..f3bd5508aa0954e7a4e230bc2211a2f0188ff7b3 100644 (file)
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -2472,28 +2472,30 @@ std::error_code BitcodeReader::parseMetadata(bool ModuleLevel) {
         return error("Invalid record");
 
       IsDistinct =
-          Record[0] || Record[8]; // All definitions should be distinct.
+          (Record[0] & 1) || Record[8]; // All definitions should be distinct.
       // Version 1 has a Function as Record[15].
       // Version 2 has removed Record[15].
       // Version 3 has the Unit as Record[15].
+      bool HasUnit = Record[0] >= 2;
+      if (HasUnit && Record.size() != 19)
+        return error("Invalid record");
       Metadata *CUorFn = getMDOrNull(Record[15]);
       unsigned Offset = Record.size() == 19 ? 1 : 0;
-      bool HasFn = Offset && dyn_cast_or_null<ConstantAsMetadata>(CUorFn);
-      bool HasCU = Offset && !HasFn;
+      bool HasFn = Offset && !HasUnit;
       DISubprogram *SP = GET_OR_DISTINCT(
           DISubprogram,
           (Context, getDITypeRefOrNull(Record[1]), getMDString(Record[2]),
            getMDString(Record[3]), getMDOrNull(Record[4]), Record[5],
            getMDOrNull(Record[6]), Record[7], Record[8], Record[9],
            getDITypeRefOrNull(Record[10]), Record[11], Record[12], Record[13],
-           Record[14], HasCU ? CUorFn : nullptr,
+           Record[14], HasUnit ? CUorFn : nullptr,
            getMDOrNull(Record[15 + Offset]), getMDOrNull(Record[16 + Offset]),
            getMDOrNull(Record[17 + Offset])));
       MetadataList.assignValue(SP, NextMetadataNo++);
 
       // Upgrade sp->function mapping to function->sp mapping.
       if (HasFn) {
-        if (auto *CMD = dyn_cast<ConstantAsMetadata>(CUorFn))
+        if (auto *CMD = dyn_cast_or_null<ConstantAsMetadata>(CUorFn))
           if (auto *F = dyn_cast<Function>(CMD->getValue())) {
             if (F->isMaterializable())
               // Defer until materialized; unmaterialized functions may not have

diff --git a/lib/Bitcode/Writer/BitcodeWriter.cpp b/lib/Bitcode/Writer/BitcodeWriter.cpp
index 82e2cab60569a7e1f544de8a9affe198b678544a..035e03e206e06327d05148d92c224d33de3ea26f 100644 (file)
--- a/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -1353,7 +1353,8 @@ void ModuleBitcodeWriter::writeDICompileUnit(const DICompileUnit *N,
 void ModuleBitcodeWriter::writeDISubprogram(const DISubprogram *N,
                                             SmallVectorImpl<uint64_t> &Record,
                                             unsigned Abbrev) {
-  Record.push_back(N->isDistinct());
+  uint64_t HasUnitFlag = 1 << 1;
+  Record.push_back(N->isDistinct() | HasUnitFlag);
   Record.push_back(VE.getMetadataOrNullID(N->getScope()));
   Record.push_back(VE.getMetadataOrNullID(N->getRawName()));
   Record.push_back(VE.getMetadataOrNullID(N->getRawLinkageName()));