[9] RFR(S): 8043284: Optimize signed integer comparison

[Tobias Hartmann]

Hi,

please review the following patch that fixes JDK-8043284.

Bug: https://bugs.openjdk.java.net/browse/JDK-8043284
Webrev: http://cr.openjdk.java.net/~thartmann/8043284/webrev.00/

== Problem ==
Similar to the previous implementation of unsigned integer comparison 
(see JDK- 8042786), signed integer comparison does only consider the 
general integer range [MinInt, MaxInt] instead of two ranges when 
comparing the result of an overflowing AddI/SubI. However, there are 
situations where one can prove that both resulting ranges are unequal to 
the tested value (see 'TestIntegerComparison::testSigned' in the 
webrev). In this case the comparison can be optimized.

== Solution ==
Similar to the fix for JDK-8042786 we compute both type ranges if the 
add/sub overflows and compare them to the tested value. If we can prove 
that the value is always unequal, we replace the BoolNode by true or 
false (depending on the test).
A jtreg test is added that triggers both the unsigned as well as the 
signed optimization.

== Testing ==
- Jtreg test (TestIntegerComparison)
- JPRT

Thanks,
Tobias
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