Hi,
div_int_const_optimize() in jit3 cannot handle
a negative dividend correctly.
Here is a simple testcase.
##################################################
class NegativeDivideConst
{
static int div4(int n)
{
return n / 4;
}
static int div8(int n)
{
return n / 8;
}
static int div16(int n)
{
return n / 16;
}
public static void main(String args[])
{
System.out.println("div4(-3) = " + div4(-3));
System.out.println("div8(-3) = " + div8(-3));
System.out.println("div16(-3) = " + div16(-3));
}
}
##################################################
>java NegativeDivideConst
div4(-3) = 0
div8(-3) = 0
div16(-3) = 0
>kaffe NegativeDivideConst
div4(-3) = -1
div8(-3) = -1
div16(-3) = -1
##################################################
Please refer to the following text for more details.
http://c2.com/cgi/wiki?ArithmeticShiftingConsideredHarmful
The attached patch also fixes a typo in check_div().
regards,
Rei
Index: kaffe/kaffevm/jit3/icode.c
===================================================================
RCS file: /cvs/kaffe/kaffe/kaffe/kaffevm/jit3/icode.c,v
retrieving revision 1.51
diff -a -u -r1.51 icode.c
--- kaffe/kaffevm/jit3/icode.c 27 Dec 2004 16:09:48 -0000 1.51
+++ kaffe/kaffevm/jit3/icode.c 11 Apr 2005 16:14:23 -0000
@@ -1450,21 +1450,24 @@
break;
case 4:
slot_alloctmp(tmp);
- lshr_int_const(tmp, src, (sizeof(int) * 8 - 1));
+ ashr_int_const(tmp, src, 1);
+ lshr_int_const(tmp, tmp, (sizeof(int) * 8 - 2));
add_int(tmp, tmp, src);
ashr_int_const(dst, tmp, 2);
slot_freetmp(tmp);
break;
case 8:
slot_alloctmp(tmp);
- lshr_int_const(tmp, src, (sizeof(int) * 8 - 1));
+ ashr_int_const(tmp, src, 2);
+ lshr_int_const(tmp, tmp, (sizeof(int) * 8 - 3));
add_int(tmp, tmp, src);
ashr_int_const(dst, tmp, 3);
slot_freetmp(tmp);
break;
case 16:
slot_alloctmp(tmp);
- lshr_int_const(tmp, src, (sizeof(int) * 8 - 1));
+ ashr_int_const(tmp, src, 3);
+ lshr_int_const(tmp, tmp, (sizeof(int) * 8 - 4));
add_int(tmp, tmp, src);
ashr_int_const(dst, tmp, 4);
slot_freetmp(tmp);
@@ -4693,7 +4696,7 @@
{
#if defined(HAVE_fakecall) || defined(HAVE_fakecall_constpool)
if (!canCatch(ANY)) {
- cbranch_int_const(obj, 0, newFakeCall(soft_divzero, pc), eq |
blink);
+ cbranch_int_const(obj, 0, newFakeCall(soft_divzero, pc), beq |
blink);
}
else
#endif
Index: test/regression/NegativeDivideConst.java
===================================================================
RCS file: /cvs/kaffe/kaffe/test/regression/NegativeDivideConst.java,v
retrieving revision 1.1
diff -a -u -r1.1 NegativeDivideConst.java
--- test/regression/NegativeDivideConst.java 13 Mar 2003 23:20:49 -0000
1.1
+++ test/regression/NegativeDivideConst.java 11 Apr 2005 16:14:29 -0000
@@ -13,33 +13,41 @@
static int div8(int n)
{
- return n / 4;
+ return n / 8;
}
static int div16(int n)
{
- return n / 4;
+ return n / 16;
}
static int div32(int n)
{
- return n / 4;
+ return n / 32;
}
public static void main(String args[])
{
- System.out.println("div2 = " + div2(-1));
- System.out.println("div4 = " + div4(-1));
- System.out.println("div8 = " + div8(-1));
- System.out.println("div16 = " + div16(-1));
- System.out.println("div32 = " + div32(-1));
+ System.out.println("div2(-1) = " + div2(-1));
+ System.out.println("div4(-1) = " + div4(-1));
+ System.out.println("div8(-1) = " + div8(-1));
+ System.out.println("div16(-1) = " + div16(-1));
+ System.out.println("div32(-1) = " + div32(-1));
+ System.out.println("div4(-3) = " + div4(-3));
+ System.out.println("div8(-3) = " + div8(-3));
+ System.out.println("div16(-3) = " + div16(-3));
+ System.out.println("div32(-3) = " + div32(-3));
}
}
/* Expected Output:
-div2 = 0
-div4 = 0
-div8 = 0
-div16 = 0
-div32 = 0
+div2(-1) = 0
+div4(-1) = 0
+div8(-1) = 0
+div16(-1) = 0
+div32(-1) = 0
+div4(-3) = 0
+div8(-3) = 0
+div16(-3) = 0
+div32(-3) = 0
*/
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