[Bitcode] AtEndOfStream should only check against the size if it's known.

This avoids an issue where AtEndOfStream mistakenly returns true at the /start/ of
a stream.

(In the rare case that the size is known and actually 0, the slow path will still
handle it correctly.)

llvm-svn: 221840

include/llvm/Bitcode/BitstreamReader.h

@@ -227,7 +227,7 @@ public:
   bool AtEndOfStream() {
     if (BitsInCurWord != 0)
       return false;
-    if (Size == NextChar)
+    if (Size != 0 && Size == NextChar)
       return true;
     fillCurWord();
     return BitsInCurWord == 0;

unittests/Bitcode/BitstreamReaderTest.cpp

@@ -0,0 +1,56 @@
+//===- BitstreamReaderTest.cpp - Tests for BitstreamReader ----------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Bitcode/BitstreamReader.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(BitstreamReaderTest, AtEndOfStream) {
+  uint8_t Bytes[4] = {
+    0x00, 0x01, 0x02, 0x03
+  };
+  BitstreamReader Reader(std::begin(Bytes), std::end(Bytes));
+  BitstreamCursor Cursor(Reader);
+
+  EXPECT_FALSE(Cursor.AtEndOfStream());
+  (void)Cursor.Read(8);
+  EXPECT_FALSE(Cursor.AtEndOfStream());
+  (void)Cursor.Read(24);
+  EXPECT_TRUE(Cursor.AtEndOfStream());
+
+  Cursor.JumpToBit(0);
+  EXPECT_FALSE(Cursor.AtEndOfStream());
+
+  Cursor.JumpToBit(32);
+  EXPECT_TRUE(Cursor.AtEndOfStream());
+}
+
+TEST(BitstreamReaderTest, AtEndOfStreamJump) {
+  uint8_t Bytes[4] = {
+    0x00, 0x01, 0x02, 0x03
+  };
+  BitstreamReader Reader(std::begin(Bytes), std::end(Bytes));
+  BitstreamCursor Cursor(Reader);
+
+  Cursor.JumpToBit(32);
+  EXPECT_TRUE(Cursor.AtEndOfStream());
+}
+
+TEST(BitstreamReaderTest, AtEndOfStreamEmpty) {
+  uint8_t Dummy = 0xFF;
+  BitstreamReader Reader(&Dummy, &Dummy);
+  BitstreamCursor Cursor(Reader);
+
+  EXPECT_TRUE(Cursor.AtEndOfStream());
+}
+
+} // end anonymous namespace

unittests/Bitcode/CMakeLists.txt

@@ -8,4 +8,5 @@ set(LLVM_LINK_COMPONENTS
 
 add_llvm_unittest(BitcodeTests
   BitReaderTest.cpp
+  BitstreamReaderTest.cpp
   )