Add a rule to simplify constant earlier in decompilation

d810/optimizers/instructions/pattern_matching/__init__.py

@@ -12,6 +12,7 @@ from d810.optimizers.instructions.pattern_matching.rewrite_or import *
 from d810.optimizers.instructions.pattern_matching.rewrite_sub import *
 from d810.optimizers.instructions.pattern_matching.rewrite_xor import *
 from d810.optimizers.instructions.pattern_matching.weird import *
+from d810.optimizers.instructions.pattern_matching.experimental import *
 
 PATTERN_MATCHING_RULES = [x() for x in get_all_subclasses(PatternMatchingRule)]
 

d810/optimizers/instructions/pattern_matching/experimental.py

@@ -0,0 +1,36 @@
+from ida_hexrays import *
+
+from d810.optimizers.instructions.pattern_matching.handler import PatternMatchingRule
+from d810.ast import AstLeaf, AstConstant, AstNode
+from d810.hexrays_formatters import  format_mop_t
+
+class ReplaceMovHigh(PatternMatchingRule):
+    PATTERN = AstNode(m_mov,
+                      AstConstant('c_0'))
+    REPLACEMENT_PATTERN = AstNode(m_or, AstConstant("new_c_0"), AstNode(m_and, AstLeaf("new_reg"), AstConstant("mask")))
+
+    def check_candidate(self, candidate):
+        # IDA does not do constant propagation for pattern such as:
+        # mov     #0x65A4.2, r6.2
+        # mov     #0x210F.2, r6^2.2
+        # jz      r0.4, r6.4
+        # Thus, we try to detect mov to r6^2 and replace by (or #0x210F0000.4, r6.4 & 0x0000ffff.4, r6.4
+        # By doing that, IDA constant propagation will work again.
+
+        if candidate.dst_mop.t != mop_r:
+            return False
+        dst_reg_name = format_mop_t(candidate.dst_mop)
+        if dst_reg_name is None:
+            return False
+        if "^2" in dst_reg_name:
+            if candidate["c_0"].mop.size != 2:
+                return False
+            candidate.add_constant_leaf("new_c_0", candidate["c_0"].value << 16, 4)
+            candidate.add_constant_leaf("mask", 0xffff, 4)
+            new_dst_reg = mop_t()
+            new_dst_reg.make_reg(candidate.dst_mop.r - 2, 4)
+            candidate.add_leaf("new_reg", new_dst_reg)
+            candidate.dst_mop = new_dst_reg
+            return True
+        else:
+            return False