Support: Implement StreamingMemoryObject::getPointer

The implementation is fairly obvious.  This is preparation for using
some blobs in bitcode.

For clarity (and perhaps future-proofing?), I moved the call to
JumpToBit in BitstreamCursor::readRecord ahead of calling
MemoryObject::getPointer, since JumpToBit can theoretically (a) read
bytes, which (b) invalidates the blob pointer.

This isn't strictly necessary the two memory objects we have:

  - The return of RawMemoryObject::getPointer is valid until the memory
    object is destroyed.

  - StreamingMemoryObject::getPointer is valid until the next chunk is
    read from the stream.  Since the JumpToBit call is only going ahead
    to a word boundary, we'll never load another chunk.

However, reordering makes it clear by inspection that the blob returned
by BitstreamCursor::readRecord will be valid.

I added some tests for StreamingMemoryObject::getPointer and
BitstreamCursor::readRecord.

llvm-svn: 264549

1 files changed, 26 insertions, 0 deletions

diff --git a/llvm/unittests/Support/StreamingMemoryObjectTest.cpp b/llvm/unittests/Support/StreamingMemoryObjectTest.cpp
index 261f2144392..836dfa9084f 100644
--- a/llvm/unittests/Support/StreamingMemoryObjectTest.cpp
+++ b/llvm/unittests/Support/StreamingMemoryObjectTest.cpp
@@ -24,6 +24,21 @@ class NullDataStreamer : public DataStreamer {
   }
 };
 
+class BufferStreamer : public DataStreamer {
+  StringRef Buffer;
+
+public:
+  BufferStreamer(StringRef Buffer) : Buffer(Buffer) {}
+  size_t GetBytes(unsigned char *OutBuffer, size_t Length) override {
+    if (Length >= Buffer.size())
+      Length = Buffer.size();
+
+    std::copy(Buffer.begin(), Buffer.begin() + Length, OutBuffer);
+    Buffer = Buffer.drop_front(Length);
+    return Length;
+  }
+};
+
 TEST(StreamingMemoryObjectTest, isValidAddress) {
   auto DS = make_unique<NullDataStreamer>();
   StreamingMemoryObject O(std::move(DS));
@@ -39,4 +54,15 @@ TEST(StreamingMemoryObjectTest, setKnownObjectSize) {
   EXPECT_EQ(8u, O.readBytes(Buf, 16, 16));
 }
 
+TEST(StreamingMemoryObjectTest, getPointer) {
+  uint8_t InputBuffer[] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07};
+  StreamingMemoryObject O(make_unique<BufferStreamer>(StringRef(
+      reinterpret_cast<const char *>(InputBuffer), sizeof(InputBuffer))));
+
+  EXPECT_TRUE(std::equal(InputBuffer + 1, InputBuffer + 2, O.getPointer(1, 2)));
+  EXPECT_TRUE(std::equal(InputBuffer + 3, InputBuffer + 7, O.getPointer(3, 4)));
+  EXPECT_TRUE(std::equal(InputBuffer + 4, InputBuffer + 8, O.getPointer(4, 5)));
+  EXPECT_TRUE(std::equal(InputBuffer, InputBuffer + 8, O.getPointer(0, 20)));
+}
+
 } // end namespace