From 607add0f2d4f1413d9d2ba8e19b9e50fa62c888b Mon Sep 17 00:00:00 2001
From: chiba <chiba@30ef5769-5b8d-40dd-aea6-55b5d6557bb3>
Date: Thu, 15 Jul 2010 16:13:25 +0000
Subject: [PATCH] better support of JSR/RET when computing MaxStack

git-svn-id: http://anonsvn.jboss.org/repos/javassist/trunk@555 30ef5769-5b8d-40dd-aea6-55b5d6557bb3
---
 src/main/javassist/bytecode/CodeAnalyzer.java | 31 +++++++++++++++----
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/src/main/javassist/bytecode/CodeAnalyzer.java b/src/main/javassist/bytecode/CodeAnalyzer.java
index e8999065..a078e1f6 100644
--- a/src/main/javassist/bytecode/CodeAnalyzer.java
+++ b/src/main/javassist/bytecode/CodeAnalyzer.java
@@ -74,6 +74,8 @@ class CodeAnalyzer implements Opcode {
         int codeLength = stack.length;
         ci.move(index);
         int stackDepth = -stack[index];
+        int[] jsrDepth = new int[1];
+        jsrDepth[0] = -1;
         while (ci.hasNext()) {
             index = ci.next();
             stack[index] = stackDepth;
@@ -82,7 +84,7 @@ class CodeAnalyzer implements Opcode {
             if (stackDepth < 1)
                 throw new BadBytecode("stack underflow at " + index);
 
-            if (processBranch(op, ci, index, codeLength, stack, stackDepth))
+            if (processBranch(op, ci, index, codeLength, stack, stackDepth, jsrDepth))
                 break;
 
             if (isEnd(op))     // return, ireturn, athrow, ...
@@ -94,7 +96,7 @@ class CodeAnalyzer implements Opcode {
     }
 
     private boolean processBranch(int opcode, CodeIterator ci, int index,
-                                  int codeLength, int[] stack, int stackDepth)
+                                  int codeLength, int[] stack, int stackDepth, int[] jsrDepth)
         throws BadBytecode
     {
         if ((IFEQ <= opcode && opcode <= IF_ACMPNE)
@@ -121,17 +123,34 @@ class CodeAnalyzer implements Opcode {
                     target = index + ci.s32bitAt(index + 1);
 
                 checkTarget(index, target, codeLength, stack, stackDepth);
-                if (stackDepth == 2)    // stackDepth is 1 if empty
+                /*
+                 * It is unknown which RET comes back to this JSR.
+                 * So we assume that if the stack depth at one JSR instruction
+                 * is N, then it is also N at other JSRs and N - 1 at all RET
+                 * instructions.  Note that STACK_GROW[JSR] is 1 since it pushes
+                 * a return address on the operand stack.
+                 */
+                if (jsrDepth[0] < 0) {
+                    jsrDepth[0] = stackDepth;
+                    return false;
+                }
+                else if (stackDepth == jsrDepth[0])
                     return false;
                 else
                     throw new BadBytecode(
-                        "sorry, cannot compute this data flow due to JSR");
+                        "sorry, cannot compute this data flow due to JSR: "
+                            + stackDepth + "," + jsrDepth[0]);
             case RET :
-                if (stackDepth == 1)    // stackDepth is 1 if empty
+                if (jsrDepth[0] < 0) {
+                    jsrDepth[0] = stackDepth + 1;
+                    return false;
+                }
+                else if (stackDepth + 1 == jsrDepth[0])
                     return true;
                 else
                     throw new BadBytecode(
-                        "sorry, cannot compute this data flow due to RET");
+                        "sorry, cannot compute this data flow due to RET: "
+                            + stackDepth + "," + jsrDepth[0]);
             case LOOKUPSWITCH :
             case TABLESWITCH :
                 index2 = (index & ~3) + 4;
-- 
2.39.5