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diff --git a/docs/BytecodeFormat.html b/docs/BytecodeFormat.html index 226cd9638b..b204c83769 100644 --- a/docs/BytecodeFormat.html +++ b/docs/BytecodeFormat.html @@ -1556,6 +1556,34 @@ describes the differences between that version and the one that <i>follows</i>. </p> </div> <!-- _______________________________________________________________________ --> +<div class="doc_subsection"><a name="vers12">Version 1.3 Differences From + 1.4</a></div> +<!-- _______________________________________________________________________ --> +<div class="doc_subsubsection">Aligned Data</div> +<div class="doc_text"> + <p>In version 1.3, certain data items were aligned to 32-bit boundaries. In + version 1.4, alignment of data was done away with completely. The need for + alignment has gone away and the only thing it adds is bytecode file size + overhead. In most cases this overhead was small. However, in functions with + large numbers of format 0 instructions (GEPs and PHIs with lots of parameters) + or regular instructions with large valued operands (e.g. because there's just + a lot of instructions in the function) the overhead can be extreme. In one + test case, the overhead was 44,000 bytes (34% of the total file size). + Consequently in release 1.4, the decision was made to eliminate alignment + altogether.</p> + <p>In version 1.3 format, the following bytecode constructs were aligned (i.e. + they were followed by one to three bytes of padding):</p> + <ul> + <li>All blocks.</li> + <li>Instructions using the long format (format 0).</li> + <li>All call instructions that called a var args function.</li> + <li>The target triple (a string field at the end of the module block).</li> + <li>The version field (immediately following the signature).</li> + </ul> + <p>None of these constructs are aligned in version 1.4</p> +</div> + +<!-- _______________________________________________________________________ --> <div class="doc_subsection"><a name="vers12">Version 1.2 Differences From 1.3</a></div> <!-- _______________________________________________________________________ --> |