[code-reflection] RFR: OpWriter block naming align with block indexes

[Adam Sotona]

On Fri, 24 May 2024 22:58:32 GMT, Paul Sandoz <psandoz at openjdk.org> wrote:

>> I propose to change OpWriter block naming conventions to be aligned with block indexes.
>> 
>> It is very hard to debug when there is no connection between debugged body and available prints provided by OpWriter.
>> This patch composes block name as composition of block indexes from super-parent-body block index down the actual block index. With fallback to the `block__<counter>` In case the block is not a part of a body.
>> 
>> This is and example of such print:
>> 
>>     %0 : java.util.function.IntUnaryOperator = lambda @loc="88:31" (%1 : int)int -> {
>>         %2 : Var<int> = var %1 @"i" @loc="88:31";
>>         %3 : int = var.load %2 @loc="89:17";
>>         %4 : int = constant @"0" @loc="89:21";
>>         %5 : boolean = gt %3 %4 @loc="89:17";
>>         cbranch %5 ^block_0_1 ^block_0_2;
>>       
>>       ^block_0_1:
>>         %6 : java.util.function.IntUnaryOperator = lambda @loc="90:38" (%7 : int)int -> {
>>             %8 : Var<int> = var %7 @"ii" @loc="90:38";
>>             %9 : int = var.load %8 @loc="91:25";
>>             %10 : int = constant @"0" @loc="91:30";
>>             %11 : boolean = lt %9 %10 @loc="91:25";
>>             cbranch %11 ^block_0_1_1 ^block_0_1_2;
>>           
>>           ^block_0_1_1:
>>             %12 : int = constant @"2" @loc="92:32";
>>             %13 : int = var.load %8 @loc="92:36";
>>             %14 : int = mul %12 %13 @loc="92:32";
>>             %15 : int = constant @"1" @loc="92:41";
>>             %16 : int = sub %14 %15 @loc="92:32";
>>             return %16 @loc="92:25";
>>           
>>           ^block_0_1_2:
>>             %17 : int = var.load %8 @loc="94:32";
>>             return %17 @loc="94:25";
>>           
>>           ^block_0_1_3:
>>             return @loc="90:38";
>>         };
>>         %18 : Var<java.util.function.IntUnaryOperator> = var %6 @"o" @loc="90:17";
>>         %19 : java.util.function.IntUnaryOperator = var.load %18 @loc="97:24";
>>         %20 : int = constant @"2" @loc="97:37";
>>         %21 : int = var.load %2 @loc="97:41";
>>         %22 : int = mul %20 %21 @loc="97:37";
>>         %23 : int = invoke %19 %22 @"java.util.function.IntUnaryOperator::applyAsInt(int)int" @loc="97:24";
>>         return %23 @loc="97:17";
>>       
>>       ^block_0_2:
>>         %24 : java.util.function.IntUnaryOperator = lambda @loc="99:38" (%25 : int)int -> {
>>             %26 : Var<int> = var %25 @"ii" @loc="99:38";
>>             %27 : int = var.load %26 @loc="100:25";
>>             %28 : int = constant @"0" @loc="100:30";
>>      ...
>
> src/java.base/share/classes/java/lang/reflect/code/writer/OpWriter.java line 58:
> 
>> 56: 
>> 57:         private String blockId(Block b) {
>> 58:             if (b.index() < 0) return "__" + blockOrdinal++;
> 
> This should always be true `b.parentBody().blocks().indexOf(this) == b.index()` - a block's index should never be negative. Are you observing such a case?

I assumed such case is possible based on the implementation comment:

    // Block is inoperable when < 0 i.e., when partially built
    int index = -1;

However it can simplify if OpWriter could never be called on a partially built block.

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PR Review Comment: https://git.openjdk.org/babylon/pull/91#discussion_r1615512846