Revert "remove store expanstion"

This reverts commit a99ccf6.

vyper/venom/__init__.py

@@ -3,6 +3,7 @@
 
 from typing import Optional
 
+from vyper.venom.passes.store_expansion import StoreExpansionPass
 from vyper.codegen.ir_node import IRnode
 from vyper.compiler.settings import OptimizationLevel
 from vyper.venom.analysis.analysis import IRAnalysesCache
@@ -56,6 +57,7 @@ def _run_passes(fn: IRFunction, optimize: OptimizationLevel) -> None:
     BranchOptimizationPass(ac, fn).run_pass()
     ExtractLiteralsPass(ac, fn).run_pass()
     RemoveUnusedVariablesPass(ac, fn).run_pass()
+    StoreExpansionPass(ac, fn).run_pass()
     DFTPass(ac, fn).run_pass()
 
 

vyper/venom/passes/store_expansion.py

@@ -0,0 +1,46 @@
+from vyper.venom.analysis.dfg import DFGAnalysis
+from vyper.venom.analysis.liveness import LivenessAnalysis
+from vyper.venom.basicblock import IRInstruction
+from vyper.venom.passes.base_pass import IRPass
+
+
+class StoreExpansionPass(IRPass):
+    """
+    This pass expands variables to their uses though `store` instructions,
+    reducing pressure on the stack scheduler
+    """
+
+    def run_pass(self):
+        dfg = self.analyses_cache.request_analysis(DFGAnalysis)
+
+        for bb in self.function.get_basic_blocks():
+            for idx, inst in enumerate(bb.instructions):
+                if inst.output is None:
+                    continue
+
+                # print("ENTER", inst)
+                self._process_inst(dfg, inst, idx)
+
+        self.analyses_cache.invalidate_analysis(LivenessAnalysis)
+        self.analyses_cache.invalidate_analysis(DFGAnalysis)
+
+    def _process_inst(self, dfg, inst, idx):
+        """
+        Process store instruction. If the variable is only used by a load instruction,
+        forward the variable to the load instruction.
+        """
+        var = inst.output
+        uses = dfg.get_uses(var)
+
+        insertion_idx = idx + 1
+
+        for use_inst in uses:
+            if use_inst.parent != inst.parent:
+                continue  # improves codesize
+
+            for i, operand in enumerate(use_inst.operands):
+                if operand == var:
+                    new_var = self.function.get_next_variable()
+                    new_inst = IRInstruction("store", [var], new_var)
+                    inst.parent.insert_instruction(new_inst, insertion_idx)
+                    use_inst.operands[i] = new_var