8267399: C2: java/text/Normalizer/ConformanceTest.java test failed with assertion #4388
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| main_limit = new CastIINode(main_limit, TypeInt::make(upward ? min_jint : orig_limit_t->_lo, | ||
| upward ? orig_limit_t->_hi : max_jint, Type::WidenMax)); |
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First, need comment.
Second, why you used min_jint and max_jint instead of main_limit->_lo and main_limit->_hi?
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Thanks for the reviewing this.
Second, why you used min_jint and max_jint instead of main_limit->_lo and main_limit->_hi?
Range check elimination changes the main loop's limit. For a loop going up, the new limit is less or equal to the initial limit. So it's less than main_limit->_hi. But it's not guaranteed to be greater or equal to main_limit->_lo. Say, main_limit is a constant, then main_limit->_lo = main_limit->_hi. The new limit can't be >= main_limit->_lo otherwise the new limit is main_limit->_lo = main_limit->_hi and the limit is unchanged.
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First, need comment.
Comment added.
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What are you saying is that low limit does not matter when stride > 0 and we can use min_jint instead of complex expression (if we want correct value). Is it right?
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This was found with Shenandoah but has nothing specific to Shenandoah.
For the inner loop of the test case:
the loop limit, len, is known to be either 1 or 2. As a consequence
the type of the iv phi is set to [0..2].
range check elimination is applied which causes the pre/main/post
loops to be added and the limit of the main loop to be adjusted. C2
computes the limit of the main loop as TypeINT:INT.
the main loop is peeled. So now the type of the iv phi is 2 and it
constant folds. Because the main loop limit has type TypeInt::INT,
the exit condition of the loop doesn't constant fold. But the loop
no longer has the shape of a counted loop because the iv phi doesn't
exist anymore.
The crash then occurs when some other loop opts is attempted and loop
strip mining verification code checks that the shape of the main loop
is that of a counted loop.
The fix I propose is to add a CastII at range elimination time that
captures the bounds of the limit before RC is applied. This way the
type of the limit is not lost and the main loop backbranch can be
properly eliminated in the chain of events above.
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