[9] RFR(S): 8158228: C1 incorrectly folds mismatched loads from stable arrays

[Tobias Hartmann]

Hi,

please review the following patch:

https://bugs.openjdk.java.net/browse/JDK-8158228
http://cr.openjdk.java.net/~thartmann/8158228/webrev.00/

Multiple tests fail since JDK 9 b110 because String.charAt() returns a wrong value for a constant string. In b110, JDK-8143407 [1] enabled C1 to constant fold stable array elements and since JDK-8150180 [2] String.value is constant. The problem is that C1 does not correctly fold mismatched loads from stable arrays. In this case, String.value is a stable byte[] and StringUTF16.charAt() is intrinsified as char load. Instead of a char load, C1 emits a byte load because it does not check for mismatched loads.

I fixed this by passing the BasicType of the mismatched load to ciArray::element_value() to ensure the correct constant is emitted. I verified that both 'Lex06403.java' and 'NewTestCase.java' pass with the fix. Also tested with JPRT and RBT (running).

Thanks,
Tobias

[1] https://bugs.openjdk.java.net/browse/JDK-8143407
[2] https://bugs.openjdk.java.net/browse/JDK-8150180