From ef56e5ba094dc7bc485c0f7cf063b8eec72188c0 Mon Sep 17 00:00:00 2001
From: Caleb Fenton <calebjfenton@gmail.com>
Date: Tue, 16 Oct 2018 17:23:16 -0700
Subject: [PATCH] Correctly track parameter register when collapsing

Reference https://github.com/CalebFenton/simplify/issues/76
---
 .../java/org/cf/smalivm/VirtualMachine.java   | 11 ++++-------
 .../org/cf/smalivm/opcode/InvokeOpTest.java   |  8 ++++++++
 .../smali/ops/invoke_static_test.smali        | 19 +++++++++++++++++++
 3 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/smalivm/src/main/java/org/cf/smalivm/VirtualMachine.java b/smalivm/src/main/java/org/cf/smalivm/VirtualMachine.java
index c078b59f1..fbd868d55 100644
--- a/smalivm/src/main/java/org/cf/smalivm/VirtualMachine.java
+++ b/smalivm/src/main/java/org/cf/smalivm/VirtualMachine.java
@@ -229,14 +229,11 @@ private void collapseMultiverse(VirtualMethod calledMethod, ExecutionGraph graph
             int parameterRegister = graph.getNodePile(0).get(0).getContext().getMethodState().getParameterStart();
             for (int parameterIndex = 0; parameterIndex < parameterTypes.size(); parameterIndex++) {
                 String type = parameterTypes.get(parameterIndex);
-                if (configuration.isImmutable(type)) {
-                    continue;
+                if (configuration.isMutable(type)) {
+                    HeapItem item = getMutableParameterConsensus(terminatingAddresses, graph, parameterRegister);
+                    int register = parameterRegisters[parameterIndex];
+                    callerMethodState.assignRegisterAndUpdateIdentities(register, item);
                 }
-
-                HeapItem item = getMutableParameterConsensus(terminatingAddresses, graph, parameterRegister);
-                int register = parameterRegisters[parameterIndex];
-                callerMethodState.assignRegisterAndUpdateIdentities(register, item);
-
                 parameterRegister += Utils.getRegisterSize(type);
             }
         }
diff --git a/smalivm/src/test/java/org/cf/smalivm/opcode/InvokeOpTest.java b/smalivm/src/test/java/org/cf/smalivm/opcode/InvokeOpTest.java
index a27b26919..b36bf3ce5 100644
--- a/smalivm/src/test/java/org/cf/smalivm/opcode/InvokeOpTest.java
+++ b/smalivm/src/test/java/org/cf/smalivm/opcode/InvokeOpTest.java
@@ -209,6 +209,14 @@ public void invokeMutateStringBuilderDoesMutateParameter() {
             VMTester.test(CLASS_NAME, "invokeMutateStringBuilder()V", initial, expected);
         }
 
+        @Test
+        public void invokeMutateStringBuilderAsThirdParameterAndFirstMutableParameterDoesMutateParameter() {
+            initial.setRegisters(0, 0x10, "I", 1, 0x20, "I", 2, new StringBuilder("i have been"), "Ljava/lang/StringBuilder;");
+            expected.setRegisters(0, 0x10, "I", 1, 0x20, "I", 2, new StringBuilder("i have been mutated"), "Ljava/lang/StringBuilder;");
+
+            VMTester.test(CLASS_NAME, "invokeMutateStringBuilderAsThirdParameterAndFirstMutableParameter()V", initial, expected);
+        }
+
         @Test
         public void invokeMutateStringDoesNotMutateParameter() {
             initial.setRegisters(0, "not mutated", "Ljava/lang/String;");
diff --git a/smalivm/src/test/resources/smali/ops/invoke_static_test.smali b/smalivm/src/test/resources/smali/ops/invoke_static_test.smali
index 837469e53..4feea44a7 100644
--- a/smalivm/src/test/resources/smali/ops/invoke_static_test.smali
+++ b/smalivm/src/test/resources/smali/ops/invoke_static_test.smali
@@ -54,6 +54,14 @@
   return-void
 .end method
 
+.method public static invokeMutateStringBuilderAsThirdParameterAndFirstMutableParameter()V
+  .locals 3
+
+  invoke-static {v0, v1, v2}, Linvoke_static_test;->mutateStringBuilderAsThirdParameterAndFirstMutableParameter(IILjava/lang/StringBuilder;)V
+
+  return-void
+.end method
+
 .method public static invokeNonExistentMethod()V
   .locals 0
 
@@ -250,6 +258,17 @@
   return-void
 .end method
 
+.method private static mutateStringBuilderAsThirdParameterAndFirstMutableParameter(IILjava/lang/StringBuilder;)V
+  .locals 1
+
+  const-string v0, " mutated"
+  invoke-virtual {p2, v0}, Ljava/lang/StringBuilder;->append(Ljava/lang/String;)Ljava/lang/StringBuilder;
+
+  const/4 p2, 0x1
+
+  return-void
+.end method
+
 # test assume maximum unknown
 .method private static set0thElementOfFirstParameterTo0IfSecondParameterIs0([II)V
   .locals 1