JDK-8148518 : Unsafe.getCharUnaligned() loads aren't folded in case of -XX:-UseUnalignedAccesses
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 9
  • Priority: P4
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2016-01-29
  • Updated: 2016-05-05
  • Resolved: 2016-02-17
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JDK 9
9 b108Fixed
Related Reports
Blocks :  
JDK-8149844 - Update test/compiler/unsafe/UnsafeGetConstantField.java once JDK-8148518 and Jake are integrated
Relates :  
JDK-8156124 - Update compiler/unsafe/UnsafeGetConstantField after JDK-8148518 is fixed
Relates :  
JDK-8078629 - VM should constant fold Unsafe.get*() loads from final fields
Description
working on JDK-8134102 I've slightly improved hotspot/test/compiler/unsafe/UnsafeGetConstantField.java test: now it also checks that even if field's value is changed, testDirect and testUnsafe return the previous value.
those changes revealed that Unsafe.getCharUnaligned() loads for @Stable and final fields aren't folded in case JVM is started w/ -XX:-UseUnalignedAccesses
Comments
attached is the changed test.
29-01-2016
type=Char flags=0 stable=true default=false post=Unaligned dumping test class to /private/tmp/run/JTwork/scratch/./TestCharUnaligned__f=0__s=true__d=false.class java.lang.RuntimeException: (assert failed: \uffff == \u0000) -- type=Char flags=8 stable=true default=false post=Unaligned dumping test class to /private/tmp/run/JTwork/scratch/./TestCharUnaligned__f=8__s=true__d=false.class java.lang.RuntimeException: (assert failed: \uffff == \u0000) -- type=Char flags=16 stable=false default=false post=Unaligned dumping test class to /private/tmp/run/JTwork/scratch/./TestCharUnaligned__f=16__s=false__d=false.class java.lang.RuntimeException: (assert failed: \uffff == \u0000) -- type=Char flags=16 stable=true default=false post=Unaligned dumping test class to /private/tmp/run/JTwork/scratch/./TestCharUnaligned__f=16__s=true__d=false.class java.lang.RuntimeException: (assert failed: \uffff == \u0000) -- type=Char flags=24 stable=false default=false post=Unaligned dumping test class to /private/tmp/run/JTwork/scratch/./TestCharUnaligned__f=24__s=false__d=false.class java.lang.RuntimeException: (assert failed: \uffff == \u0000) -- type=Char flags=24 stable=true default=false post=Unaligned dumping test class to /private/tmp/run/JTwork/scratch/./TestCharUnaligned__f=24__s=true__d=false.class java.lang.RuntimeException: (assert failed: \uffff == \u0000)
29-01-2016