fix[venom]: fix invalid phis after SCCP

vyper/venom/__init__.py

@@ -19,6 +19,7 @@
 from vyper.venom.passes.sccp import SCCP
 from vyper.venom.passes.simplify_cfg import SimplifyCFGPass
 from vyper.venom.passes.store_elimination import StoreElimination
+from vyper.venom.passes.remove_invalid_phi_nodes import RemoveInvalidPhiPass
 from vyper.venom.venom_to_assembly import VenomCompiler
 
 DEFAULT_OPT_LEVEL = OptimizationLevel.default()
@@ -50,6 +51,7 @@ def _run_passes(fn: IRFunction, optimize: OptimizationLevel) -> None:
     Mem2Var(ac, fn).run_pass()
     MakeSSA(ac, fn).run_pass()
     SCCP(ac, fn).run_pass()
+    RemoveInvalidPhiPass(ac, fn).run_pass()
     StoreElimination(ac, fn).run_pass()
     SimplifyCFGPass(ac, fn).run_pass()
     AlgebraicOptimizationPass(ac, fn).run_pass()

vyper/venom/passes/remove_invalid_phi_nodes.py

@@ -0,0 +1,36 @@
+from vyper.venom.basicblock import IRBasicBlock, IRLabel, IRInstruction, IRVariable
+from vyper.venom.passes.base_pass import IRPass
+from vyper.venom.analysis.dfg import DFGAnalysis
+from vyper.venom.analysis.cfg import CFGAnalysis
+
+class RemoveInvalidPhiPass(IRPass):
+    dfg : DFGAnalysis
+
+    def run_pass(self):
+        self.analyses_cache.request_analysis(CFGAnalysis)
+        self.dfg = self.analyses_cache.request_analysis(DFGAnalysis)
+
+        for bb in self.function.get_basic_blocks():
+            for inst in bb.instructions.copy():
+                if inst.opcode == "phi":
+                    self._handle_phi(inst)
+
+    def _handle_phi(self, phi_inst : IRInstruction) -> bool:
+        if len(phi_inst.parent.cfg_in) != 1:
+            return False
+
+        src_bb : IRBasicBlock = phi_inst.parent.cfg_in.first()
+        assert isinstance(src_bb, IRBasicBlock)
+
+        from_src_bb = filter(lambda x : x[0] == src_bb.label, phi_inst.phi_operands)
+        operands = list(map(lambda x : x[1], from_src_bb))
+
+        assert len(operands) == 1
+        assert isinstance(operands[0], IRVariable)
+        phi_inst.output.value = operands[0]
+        phi_inst.parent.remove_instruction(phi_inst)
+
+        return True
+
+
+

vyper/venom/passes/simplify_cfg.py

@@ -11,24 +11,21 @@ class SimplifyCFGPass(IRPass):
     def _merge_blocks(self, a: IRBasicBlock, b: IRBasicBlock):
         a.instructions.pop()
         for inst in b.instructions:
-            assert inst.opcode != "phi", "Not implemented yet"
-            if inst.opcode == "phi":
-                a.instructions.insert(0, inst)
-            else:
-                inst.parent = a
-                a.instructions.append(inst)
+            assert inst.opcode != "phi", f"Instruction should never be phi {inst}"
+            inst.parent = a
+            a.instructions.append(inst)
 
         # Update CFG
         a.cfg_out = b.cfg_out
         if len(b.cfg_out) > 0:
-            next_bb = b.cfg_out.first()
-            next_bb.remove_cfg_in(b)
-            next_bb.add_cfg_in(a)
-
-            for inst in next_bb.instructions:
-                if inst.opcode != "phi":
-                    break
-                inst.operands[inst.operands.index(b.label)] = a.label
+            for next_bb in b.cfg_out:
+                next_bb.remove_cfg_in(b)
+                next_bb.add_cfg_in(a)
+
+                for inst in next_bb.instructions:
+                    if inst.opcode != "phi":
+                        break
+                    inst.operands[inst.operands.index(b.label)] = a.label
 
         self.function.remove_basic_block(b)