ASTI: prune variables not used from the lifting

Author: sipma

chb/astinterface/ASTICodeTransformer.py

@@ -47,8 +47,10 @@ class ASTICodeTransformer(ASTIdentityTransformer):
 
     def __init__(
             self,
-            astinterface: "ASTInterface") -> None:
+            astinterface: "ASTInterface",
+            variablesused: List[str] = []) -> None:
         self._astinterface = astinterface
+        self._variablesused = variablesused
 
     @property
     def astinterface(self) -> "ASTInterface":
@@ -58,6 +60,10 @@ def astinterface(self) -> "ASTInterface":
     def provenance(self) -> "ASTIProvenance":
         return self.astinterface.astiprovenance
 
+    @property
+    def variables_used(self) -> List[str]:
+        return self._variablesused
+
     def transform_stmt(self, stmt: AST.ASTStmt) -> AST.ASTStmt:
         return stmt.transform(self)
 
@@ -98,12 +104,6 @@ def transform_instruction_sequence_stmt(
                         and not self.provenance.has_expose_instruction(instr.instrid)):
                     chklogger.logger.info(
                         "Remove [%s]: has ssa value", str(instr))
-                elif self.provenance.has_active_lval_defuse_high(instr.lhs.lvalid):
-                    chklogger.logger.info(
-                        "Transform [%s]: active lval_defuse_high: %s",
-                        str(instr),
-                        self.provenance.active_lval_defuse_high(instr.lhs.lvalid))
-                    instrs.append(instr)
                 elif self.provenance.has_lval_store(instr.lhs.lvalid):
                     chklogger.logger.info(
                         "Transform [%s]: lval_store", str(instr))
@@ -116,6 +116,15 @@ def transform_instruction_sequence_stmt(
                     chklogger.logger.info(
                         "Transform [%s]: global lhs", str(instr))
                     instrs.append(instr)
+                elif str(instr.lhs) not in self.variables_used:
+                    chklogger.logger.info(
+                        "Remove [%s]: lhs is not used")
+                elif self.provenance.has_active_lval_defuse_high(instr.lhs.lvalid):
+                    chklogger.logger.info(
+                        "Transform [%s]: active lval_defuse_high: %s",
+                        str(instr),
+                        self.provenance.active_lval_defuse_high(instr.lhs.lvalid))
+                    instrs.append(instr)
                 else:
                     chklogger.logger.info("Transform [%s]: remove", str(instr))
             else:

chb/astinterface/ASTInterface.py

@@ -561,12 +561,14 @@ def add_symbol(
             name: str,
             vtype: Optional[AST.ASTTyp] = None,
             parameter: Optional[int] = None,
-            globaladdress: Optional[int] = None) -> AST.ASTVarInfo:
+            globaladdress: Optional[int] = None,
+            ssa:bool = False) -> AST.ASTVarInfo:
         return self.astree.add_symbol(
             name,
             vtype=vtype,
             parameter=parameter,
-            globaladdress=globaladdress)
+            globaladdress=globaladdress,
+            ssa=ssa)
 
     def add_formal(
             self,
@@ -1050,7 +1052,7 @@ def mk_ssa_register_varinfo(
             ssaid = self._ssa_prefix_counters[ssaprefix]
             self._ssa_prefix_counters[ssaprefix] += 1
             vname = ssaprefix + "_" + str(ssaid)
-        varinfo = self.add_symbol(vname, vtype=vtype)
+        varinfo = self.add_symbol(vname, vtype=vtype, ssa=True)
         self._ssa_intros.setdefault(iaddr, {})
         self._ssa_intros[iaddr][name] = varinfo
         if save_loc:

chb/astinterface/ASTInterfaceFunction.py

@@ -222,7 +222,13 @@ def mk_high_level_ast(
                 annotations=self.astinterface.annotations)
             print(iprettyprinter.to_c(ast))
 
-        codetransformer = ASTICodeTransformer(self.astinterface)
+        variablesused = ast.variables_used()
+
+        codetransformer = ASTICodeTransformer(self.astinterface, list(variablesused))
+        transformedcode = codetransformer.transform_stmt(ast)
+
+        variablesused = transformedcode.variables_used()
+        codetransformer = ASTICodeTransformer(self.astinterface, list(variablesused))
         transformedcode = codetransformer.transform_stmt(ast)
 
         if self.verbose: