Fix for issue #10.

git-svn-id: http://llvm-py.googlecode.com/svn/trunk@59 8d1e9007-1d4e-0410-b67e-1979fd6579aa

llvm/core.py

@@ -1940,8 +1940,11 @@ class Builder(object):
         Next instruction inserted will be first one in the block."""
         # Avoids using "blk.instructions", which will fetch all the
         # instructions into a list. Don't try this at home, though.
-        first_inst = Instruction(_core.LLVMGetFirstInstruction(self.block.ptr))
-        self.position_before(first_inst)
+        inst_ptr = _core.LLVMGetFirstInstruction(self.block.ptr)
+        if inst_ptr:
+            # Issue #10: inst_ptr can be None if b/b has no insts.
+            inst = Instruction(inst_ptr)
+            self.position_before(inst)
 
     def position_at_end(self, bblk):
         """Position the builder at the end of the given block.

test/issue10.py

@@ -0,0 +1,20 @@
+
+from llvm.core import *
+import llvm._core
+
+m = Module.new('a')
+ti = Type.int()
+tf = Type.function(ti, [ti, ti])
+
+f = m.add_function(tf, "func1")
+
+bb = f.append_basic_block('entry')
+
+b = Builder.new(bb)
+
+# There are no instructions in bb. Positioning of the
+# builder at beginning (or end) should succeed (trivially).
+
+b.position_at_end(bb)
+b.position_at_beginning(bb)
+