[14] RFR(S): 8230062: assert(i == p->size()-1) failed: must be last element of the pack

[Christian Hagedorn]

Hi

Please review the following patch:
https://bugs.openjdk.java.net/browse/JDK-8230062
http://cr.openjdk.java.net/~chagedorn/8230062/webrev.00/

The assertion is too strong. There are cases where a reduction chain is 
put into a superword pack but an intermediate result is used outside of 
the loop (see test case and [1]). This triggers the assertion failure. 
Moreover, it would be incorrect to 'continue' in the loop on line 2054 
(= allowing a replacement with a vector instruction) and not exclude 
this pack.

The fix simply adds the assertion check as a condition to the continue 
statement. If we encounter such an intermediate result use outside of 
the loop then is_vector_use() returns false and we do not use a vector 
instruction (i.e. return false on line 2056).

Thank you!

Best regards,
Christian


[1] 
https://bugs.openjdk.java.net/secure/attachment/84959/IntermediateResultUse.png