[gcjx] Patch: FYI: bytecode generation bug

[gcjx] Patch: FYI: bytecode generation bug

[Tom Tromey]

I'm checking this in on the gcjx branch.

Mark pointed out a bytecode generation bug.  The test case:

    public class ifgt
    {
      public static void t(int i)
      {
        if (0 > i)
          System.out.println("negative");
      }
      public static void main(String[] args)
      {
        t(0);
      }
    }

We were improperly optimizing the 'if'.
Fixed as appended.

Tom

Index: ChangeLog
from  Tom Tromey  <tromey@redhat.com>
	* bytecode/generate.cc (handle_comparison): Use flip_if_opcode.
	* bytecode/byteutil.hh (flip_if_opcode): New function.

Index: bytecode/generate.cc
===================================================================
--- bytecode/generate.cc	(revision 108415)
+++ bytecode/generate.cc	(working copy)
@@ -2545,7 +2545,7 @@
       if (lhs->constant_p ()
 	  && jint (intb->convert (lhs->type (), lhs->value ())) == 0)
 	{
-	  base = invert_if_opcode (zero_if_opcode (base));
+	  base = flip_if_opcode (zero_if_opcode (base));
 	  {
 	    push_expr_target push (this, ON_STACK);
 	    rhs->visit (this);
Index: bytecode/byteutil.hh
===================================================================
--- bytecode/byteutil.hh	(revision 108809)
+++ bytecode/byteutil.hh	(working copy)
@@ -31,8 +31,8 @@
   return java_opcode (op_ifeq + base - op_if_icmpeq);
 }
 
-/// Invert a comparison opcode.  For instance, given op_if_cmpge, this
-/// will return op_if_cmplt.
+/// Invert the sense of a comparison opcode.  For instance, given
+/// op_if_cmpge, this will return op_if_cmplt.
 inline java_opcode
 invert_if_opcode (java_opcode base)
 {
@@ -43,6 +43,56 @@
   return java_opcode ((base & 1) ? base + 1 : base - 1);
 }
 
+/// Flip a comparison opcode.  This differs from 'invert' in that it
+/// acts as if the left and right sides of the comparison are also
+/// swapped.  So, for op_if_cmpge, it will return op_if_cmple.
+inline java_opcode
+flip_if_opcode (java_opcode base)
+{
+  switch (base)
+    {
+    case op_ifeq:
+    case op_ifne:
+    case op_if_icmpeq:
+    case op_if_icmpne:
+    case op_if_acmpeq:
+    case op_if_acmpne:
+    case op_ifnull:
+    case op_ifnonnull:
+      // Nothing.
+      break;
+    case op_iflt:
+      base = op_ifgt;
+      break;
+    case op_ifge:
+      base = op_ifle;
+      break;
+    case op_ifgt:
+      base = op_iflt;
+      break;
+    case op_ifle:
+      base = op_ifge;
+      break;
+    case op_if_icmplt:
+      base = op_if_icmpgt;
+      break;
+    case op_if_icmpge:
+      base = op_if_icmple;
+      break;
+    case op_if_icmpgt:
+      base = op_if_icmplt;
+      break;
+    case op_if_icmple:
+      base = op_if_icmpge;
+      break;
+
+    default:
+      assert (0);
+    }
+
+  return base;
+}
+
 /// Return true if the value is a 'return' bytecode of any kind.
 inline bool
 return_p (int op)