Adding better register tracking through locals and fixing branches.

LLVM does an amazing job of optimizing this. There are many opportunities
to make it better, too, by preventing spilling where not required or only
spilling/filling things when needed.

src/cpu/sdb.cc

@@ -588,6 +588,20 @@ int SymbolDatabase::AnalyzeFunction(FunctionSymbol* fn) {
         ends_fn = true;
       }
       ends_block = true;
+    } else if (i.code == 0x4E800420) {
+      // bctr -- unconditional branch to CTR.
+      // This is generally a jump to a function pointer (non-return).
+      block->outgoing_type = FunctionBlock::kTargetCTR;
+      if (furthest_target > addr) {
+        // Remaining targets within function, not end.
+        XELOGSDB("ignoring bctr %.8X (branch to %.8X)\n", addr,
+                 furthest_target);
+      } else {
+        // Function end point.
+        XELOGSDB("function end %.8X\n", addr);
+        ends_fn = true;
+      }
+      ends_block = true;
     } else if (i.type->opcode == 0x48000000) {
       // b/ba/bl/bla
       uint32_t target = XEEXTS26(i.I.LI << 2) + (i.I.AA ? 0 : (int32_t)addr);