[llvm] r247847 - Allow BackpatchWord to be called for non-32-bit aligned words, and

[Teresa Johnson via llvm-commits]

Author: tejohnson
Date: Wed Sep 16 15:41:43 2015
New Revision: 247847

URL: http://llvm.org/viewvc/llvm-project?rev=247847&view=rev
Log:
Allow BackpatchWord to be called for non-32-bit aligned words, and
from outside the BitstreamWriter.

Split out of patch D12536 (Function bitcode index in Value Symbol Table
and lazy reading support), which will use it to patch in the VST offset.

Modified:
    llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h

Modified: llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h?rev=247847&r1=247846&r2=247847&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h (original)
+++ llvm/trunk/include/llvm/Bitcode/BitstreamWriter.h Wed Sep 16 15:41:43 2015
@@ -63,12 +63,6 @@ class BitstreamWriter {
   };
   std::vector<BlockInfo> BlockInfoRecords;
 
-  // BackpatchWord - Backpatch a 32-bit word in the output with the specified
-  // value.
-  void BackpatchWord(unsigned ByteNo, unsigned NewWord) {
-    support::endian::write32le(&Out[ByteNo], NewWord);
-  }
-
   void WriteByte(unsigned char Value) {
     Out.push_back(Value);
   }
@@ -105,6 +99,23 @@ public:
   // Basic Primitives for emitting bits to the stream.
   //===--------------------------------------------------------------------===//
 
+  /// Backpatch a 32-bit word in the output at the given bit offset
+  /// with the specified value.
+  void BackpatchWord(uint64_t BitNo, unsigned NewWord) {
+    unsigned ByteNo = BitNo / 8;
+    if ((BitNo & 7) == 0) {
+      // Already 8-bit aligned
+      support::endian::write32le(&Out[ByteNo], NewWord);
+    } else {
+      uint64_t CurDWord = support::endian::read64le(&Out[ByteNo]);
+      unsigned StartBit = BitNo & 7;
+      // Currently expect to backpatch 0-value placeholders.
+      assert(((CurDWord >> StartBit) & 0xffffffff) == 0);
+      CurDWord |= NewWord << StartBit;
+      support::endian::write64le(&Out[ByteNo], CurDWord);
+    }
+  }
+
   void Emit(uint32_t Val, unsigned NumBits) {
     assert(NumBits && NumBits <= 32 && "Invalid value size!");
     assert((Val & ~(~0U >> (32-NumBits))) == 0 && "High bits set!");
@@ -234,10 +245,10 @@ public:
 
     // Compute the size of the block, in words, not counting the size field.
     unsigned SizeInWords = GetWordIndex() - B.StartSizeWord - 1;
-    unsigned ByteNo = B.StartSizeWord*4;
+    uint64_t BitNo = B.StartSizeWord * 32;
 
     // Update the block size field in the header of this sub-block.
-    BackpatchWord(ByteNo, SizeInWords);
+    BackpatchWord(BitNo, SizeInWords);
 
     // Restore the inner block's code size and abbrev table.
     CurCodeSize = B.PrevCodeSize;