question about bci in LIRFrameState for DeoptimizeOp

[Thomas Wuerthinger]

I think the guards for the array access might have been moved before the field store. Can you check in the machine code whether the deoptimization is indeed *after* the field store? - thomas

On 20 Nov 2013, at 22:08, Deneau, Tom <tom.deneau at amd.com> wrote:

> Thomas --
> 
> I retried this experiment with a java snippet that I thought would have a side effect, incrementing a field
>    public int intFromArrayLonger(int[] ary, int idx) {
>        dummyField++;
>        return ary[idx];
>    }
> 
> But I still saw a info.bci of 0.
> 
> -- Tom D
> 
> 
> 
> -----Original Message-----
> From: Thomas Wuerthinger [mailto:thomas.wuerthinger at oracle.com] 
> Sent: Wednesday, November 20, 2013 2:40 PM
> To: Deneau, Tom
> Cc: graal-dev at openjdk.java.net
> Subject: Re: question about bci in LIRFrameState for DeoptimizeOp
> 
> Graal understands that it can safely replay bytecodes without side effects. Therefore the target bci of a deoptimization will reflect the last side effecting instruction (or the beginning of the method if no such instruction exists). Gilles wrote a paper describing in more details how deoptimization works in Graal and we will publish it shortly as part of the Graal documentation. - thomas
> 
> On 20 Nov 2013, at 21:17, Deneau, Tom <tom.deneau at amd.com> wrote:
> 
>> I was looking at the AMD64DeoptimizeOp.emitCode routine which is
>>       AMD64Call.directCall(tasm, masm, 
>> tasm.foreignCalls.lookupForeignCall(UNCOMMON_TRAP), null, false, 
>> info);
>> 
>> When I look at the LIRFrameState info which is passed to UNCOMMON_TRAP, the bci always seems to be 0.
>> Why is that?
>> 
>> For example, compiling this small snippet thru AMD64 backend
>>   public int intFromArray(int[] ary, int idx) {
>>       return ary[idx];
>>   }
>> 
>> with bytecodes
>> public int intFromArray(int[], int);
>>   Code:
>>      0: aload_1       
>>      1: iload_2       
>>      2: iaload        
>>      3: ireturn       
>> 
>> when I get to AMD64DeoptimizeOp.emitCode, I see info = "at 
>> com.oracle.graal.compiler.test.BasicTest2.intFromArray(BasicTest2.java:46) [bci: 0]
>>           |0  |1     |2    
>>  locals:  |-  |v0|a  |v1|i "
>> 
>> I would have expected the bci in this case to be 2, referring to the iaload instruction.
>> 
>> -- Tom
>> 
>> 
> 
> 
>