Begin adding experimental support for preserving use-list ordering of bitcode

files.  First, add a new block USELIST_BLOCK to the bitcode format.  This is 
where USELIST_CODE_ENTRYs will be stored.  The format of the USELIST_CODE_ENTRYs
have not yet been defined.  Add support in the BitcodeReader for parsing the
USELIST_BLOCK.
Part of rdar://9860654 and PR5680.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146078 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 25 insertions, 0 deletions

diff --git a/lib/Bitcode/Writer/BitcodeWriter.cpp b/lib/Bitcode/Writer/BitcodeWriter.cpp
index e758f94..48f60bc 100644
--- a/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -23,6 +23,7 @@
 #include "llvm/Operator.h"
 #include "llvm/ValueSymbolTable.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/raw_ostream.h"
@@ -31,6 +32,12 @@
 #include <map>
 using namespace llvm;
 
+static cl::opt<bool>
+EnablePreserveUseListOrdering("enable-bc-uselist-preserve",
+                              cl::desc("Turn on experimental support for "
+                                       "use-list order preservation."),
+                              cl::init(false), cl::Hidden);
+
 /// These are manifest constants used by the bitcode writer. They do not need to
 /// be kept in sync with the reader, but need to be consistent within this file.
 enum {
@@ -1571,6 +1578,20 @@ static void WriteBlockInfo(const ValueEnumerator &VE, BitstreamWriter &Stream) {
   Stream.ExitBlock();
 }
 
+// Emit use-lists.
+static void WriteModuleUseLists(const Module *M, ValueEnumerator &VE,
+                                BitstreamWriter &Stream) {
+  Stream.EnterSubblock(bitc::USELIST_BLOCK_ID, 3);
+
+  // Emit a bogus record for testing purposes.
+  SmallVector<uint64_t, 64> Record;
+  Record.push_back(0);
+  Stream.EmitRecord(bitc::USELIST_CODE_ENTRY, Record);
+
+  // TODO: Tons.
+
+  Stream.ExitBlock();
+}
 
 /// WriteModule - Emit the specified module to the bitstream.
 static void WriteModule(const Module *M, BitstreamWriter &Stream) {
@@ -1616,6 +1637,10 @@ static void WriteModule(const Module *M, BitstreamWriter &Stream) {
   // Emit names for globals/functions etc.
   WriteValueSymbolTable(M->getValueSymbolTable(), VE, Stream);
 
+  // Emit use-lists.
+  if (EnablePreserveUseListOrdering)
+    WriteModuleUseLists(M, VE, Stream);
+
   Stream.ExitBlock();
 }