compiler: mark loads of kernel constant attributes as load invariant.

whitequark · whitequark · commit 418f0a5234a9 · 2016-03-28T00:44:32.000Z
Also, enable LICM, since it can take advantage of this.
diff --git a/artiq/compiler/targets.py b/artiq/compiler/targets.py
@@ -105,6 +105,7 @@ def optimize(self, llmodule):
         llpassmgr.add_instruction_combining_pass()
         llpassmgr.add_gvn_pass()
         llpassmgr.add_cfg_simplification_pass()
+        llpassmgr.add_licm_pass()
 
         # Clean up after optimizing.
         llpassmgr.add_dead_arg_elimination_pass()
diff --git a/artiq/compiler/transforms/llvm_ir_generator.py b/artiq/compiler/transforms/llvm_ir_generator.py
@@ -796,7 +796,9 @@ def process_GetAttr(self, insn):
             else:
                 llptr = self.llbuilder.gep(obj, [self.llindex(0), self.llindex(index)],
                                            inbounds=True, name="ptr.{}".format(insn.name))
-                return self.llbuilder.load(llptr, name="val.{}".format(insn.name))
+                llval = self.llbuilder.load(llptr, name="val.{}".format(insn.name))
+                llval.metadata['invariant.load'] = self.empty_metadata
+                return llval
 
     def process_SetAttr(self, insn):
         typ, attr = insn.object().type, insn.attr
