instruction,
use <tt>TargetInstrInfo::get(opcode)::ImplicitUses</tt>. Pre-colored
registers impose constraints on any register allocation algorithm. The
- register allocator must make sure that none of them is been overwritten by
+ register allocator must make sure that none of them are overwritten by
the values of virtual registers while still alive.</p>
</div>
different register allocators:</p>
<ul>
- <li><i>Simple</i> — This is a very simple implementation that does not
- keep values in registers across instructions. This register allocator
- immediately spills every value right after it is computed, and reloads all
- used operands from memory to temporary registers before each
- instruction.</li>
-
- <li><i>Local</i> — This register allocator is an improvement on the
- <i>Simple</i> implementation. It allocates registers on a basic block
- level, attempting to keep values in registers and reusing registers as
- appropriate.</li>
-
<li><i>Linear Scan</i> — <i>The default allocator</i>. This is the
well-know linear scan register allocator. Whereas the
<i>Simple</i> and <i>Local</i> algorithms use a direct mapping
implementation technique, the <i>Linear Scan</i> implementation
uses a spiller in order to place load and stores.</li>
+
+ <li><i>Fast</i> — This register allocator is the default for debug
+ builds. It allocates registers on a basic block level, attempting to keep
+ values in registers and reusing registers as appropriate.</li>
+
+ <li><i>PBQP</i> — A Partitioned Boolean Quadratic Programming (PBQP)
+ based register allocator. This allocator works by constructing a PBQP
+ problem representing the register allocation problem under consideration,
+ solving this using a PBQP solver, and mapping the solution back to a
+ register assignment.</li>
+
</ul>
<p>The type of register allocator used in <tt>llc</tt> can be chosen with the
<div class="doc_code">
<pre>
-$ llc -regalloc=simple file.bc -o sp.s;
-$ llc -regalloc=local file.bc -o lc.s;
$ llc -regalloc=linearscan file.bc -o ln.s;
+$ llc -regalloc=fast file.bc -o fa.s;
+$ llc -regalloc=pbqp file.bc -o pbqp.s;
</pre>
</div>