Hi, Egor. I checked the dump IR of an simple example with "if (obj !=
null)". Following are the details:
=====================================
The simple example:
public class Ldnull
{
public static void main(String arg[])
{
Integer i = null;
int flag = Integer.parseInt(arg[0]);
if (flag == 0)
i = new Integer(0);
if (i != null)
System.out.println("i: "+i);
}
}
=====================================
Just before hir2lir:
Block ENTRY_L0:
Predecessors:
Successors: L9 UNWIND
I0:--- MethodEntry(Ldnull::main): () bcmap:0
I5:defarg -) g1:cls:java/lang/String[]
I7:ldcnul #null -) t3:null_object * *// for
Integer i = null;
I8:stvar t3 -) v1:cls:.Unresolved // for Integer i
= null;
I10:chknull g1 -) g5:tau bcmap:4
GOTO L9
Block L2:
Predecessors: L12 L16
Successors: L4 L3
I2:L2: bcmap:22
I33:ldvar v1 -) g23:cls:.Unresolved // for if (i !=
null)
I34:if cz.obj g23 goto L4 // for if (i !=
null)
GOTO L3
=====================================
After hir2lir:
BB_1
PersistentId = 0
ExecCnt = 10000
Loop: Depth=0, !hdr, hdr=NULL
Predcessors: BB_0_prolog
Successors: BB_2 [Prob=1](Br=I62) UN_29 [Prob=1e-007] BB_33
[Prob=0](Br=I62)
I1: (AD:v0:cls:.Unresolved) =CopyPseudoInst/MOV
(AU:t2(1137246208):null_object) * *// for Integer i = null;
I61: (ID:v13(EFLGS):U_32) =CMP
t1:cls:java/lang/String[],o108(1137246208):cls:java/lang/String[]
I62: JZ BB_33 o109(0):I_32 (IU:v13(EFLGS):U_32)
BB_12
PersistentId = 2
ExecCnt = 9999.99
Loop: Depth=0, !hdr, hdr=NULL
Predcessors: BB_6 BB_11
Successors: BB_30_epilog [Prob=0.241379](Br=I27) BB_13
[Prob=0.758621](Br=I27)
I25: (AD:t43:cls:.Unresolved) =CopyPseudoInst/MOV
(AU:v0:cls:.Unresolved) // for if (i != null)
I26: (ID:v13(EFLGS):U_32) =CMP
t43:cls:.Unresolved,t44(1137246208):cls:.Unresolved // for if (i != null)
I27: JZ BB_30_epilog t45(0):I_32 (IU:v13(EFLGS):U_32)
=====================================
After final pass, CMP is about two 64-bit registers (RBX and R12). Though
the flag register is in 32-bit, I don't it is a truncation.
BB_1
PersistentId = 0
ExecCnt = 10000
Loop: Depth=0, !hdr, hdr=NULL
Predcessors: BB_0_prolog
Successors: BB_2 [Prob=1](Br=I62) UN_29 [Prob=1e-007] BB_33
[Prob=1e-007](Br=I62)
Layout Succ: BB_2
Block code address: 00000000660D000D
00000000660D000D I393: MOV
v0(R12):cls:.Unresolved,t2(1137246208):null_object * *// for Integer i =
null;
00000000660D0017 I392: MOV
t150(R11):cls:java/lang/String[],t108(1137246208):cls:java/lang/String[]
00000000660D0021 I61: (ID:v13(EFLGS):U_32) =CMP
t1(RCX):cls:java/lang/String[],t150(R11):cls:java/lang/String[]
00000000660D0024 I62: JZ BB_33 t109(1577):I_32 (IU:v13(EFLGS):U_32)
BB_12
PersistentId = 2
ExecCnt = 9999.99
Loop: Depth=0, !hdr, hdr=NULL
Predcessors: BB_6 BB_11
Successors: BB_30_epilog [Prob=0.241379](Br=I27) BB_13
[Prob=0.758621](Br=I27)
Layout Succ: BB_13
Block code address: 00000000660D0132
00000000660D0132 I365: MOV
t43(RBX):cls:.Unresolved,v0(R12):cls:.Unresolved // for if (i != null)
00000000660D0135 I364: MOV
t153(R12):cls:.Unresolved,t44(1137246208):cls:.Unresolved // for if (i !=
null)
00000000660D013F I26: (ID:v13(EFLGS):U_32) =CMP
t43(RBX):cls:.Unresolved,t153(R12):cls:.Unresolved // for if (i != null)
00000000660D0142 I27: JZ BB_30_epilog t45(660):I_32 (IU:v13(EFLGS):U_32)
=====================================
Any comments? Thanks. -Xiaoming
On Fri, Feb 6, 2009 at 6:16 PM, Egor Pasko <[email protected]> wrote:
> On the 0x550 day of Apache Harmony xiaoming gu wrote:
> > In latest version, I couldn't see the code mentioned in this JIRA.
>
> me too :(
>
> > And the only operations about heap base in HIR2LIR pass are for
> > zeroForComparison, ldnull, simpleLdInd, simpleStInd and
> > ldRef. Thanks.
>
> so, to sum up the compressed mode operation: zeroForComparison,
> simpleLdInd and simpleStInd all make a copy of heap base imm operand
> via mov (heapBaseOpnd() does that). Seems to be right.
>
> But ldnull does not do that. I understand that add/sub to ldnull imm
> operand will never happen on the code selection stage. But what about
> cmp? Suppose cmp accepts this 64 bit imm operand (heap base), then
> bang, it is truncated by encoder.
>
> Thinking of a possible reproducer in java: "if (obj != null) { ... }",
> seems like too common to be working incorrectly :) Still I do not
> understand what happens in this case. Xiaoming, do you have a clue?
>
> --
> Egor Pasko
>
>
--
China Runtime Technologies Lab,
SSG/SSD/MRTC, Intel
