Unhide compressed refs logic from Unsafe CAS codegen #20400
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Disables code on Power and Z that hides compressedrefs logic from the fast path code generation for the following recognized methods: sun_misc_Unsafe_compareAndSwapObject_jlObjectJjlObjectjlObject_Z jdk_internal_misc_Unsafe_compareAndExchangeObject jdk_internal_misc_Unsafe_compareAndExchangeReference Fast path code generation for those recognized methods is updated to handle compressedrefs. Original behavior can be restored by setting the TR_UseOldCompareAndSwapObject environment variable. This behavior matches the X implementation which has already disabled the compressedrefs hiding logic when the envvar is not set. Signed-off-by: jimmyk <[email protected]>
| // Hiding compressedref logic from CodeGen doesn't seem a good practise, the evaluator always need the uncompressedref node for write barrier, | ||
| // therefore, this part is deprecated. It'll be removed once P and Z update their corresponding evaluators. | ||
| // Hiding compressedref logic from CodeGen isn't a good practice, and the evaluator still needs the uncompressedref node for write barriers. | ||
| // Therefore, this part is deprecated. It can only be activated on X, P or Z with the TR_UseOldCompareAndSwapObject envvar. | ||
| static bool UseOldCompareAndSwapObject = (bool)feGetEnv("TR_UseOldCompareAndSwapObject"); |
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Something that already in code, but not related to overall changes, Should we change UseOldCompareAndSwapObject to useOldCompareAndSwapObject ?
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I can change this.
| static bool UseOldCompareAndSwapObject = (bool)feGetEnv("TR_UseOldCompareAndSwapObject"); | ||
| static bool disableCASInlining = feGetEnv("TR_DisableCASInlining") != NULL; | ||
| if (self()->comp()->useCompressedPointers() && ((UseOldCompareAndSwapObject && (self()->comp()->target().cpu.isARM64() || !disableCASInlining)) || !(self()->comp()->target().cpu.isX86() || self()->comp()->target().cpu.isARM64()))) | ||
| if (((self()->comp()->target().cpu.isX86() && !disableCASInlining) || self()->comp()->target().cpu.isPower() || self()->comp()->target().cpu.isZ()) && |
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Hmm, bit condfusing, disableCASInlining is only checked on x86 not on P and Z. If this is intended, We should have a comment.
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This is intended. The TR_DisableCASInlining envvar to disable inlining of both Unsafe compareAndSwap and compareAndExchange only has support on X. That's why the check is only on X.
Turning on TR_DisableCASInlining and TR_UseOldCompareAndSwapObject at the same time doesn't actually make sense since if CAS inlining is disabled, it won't use either of the compare and swap implementations. But, without this change it would crash and I didn't want that.
I will add a comment explaining that the change is because the TR_DisableCASInlining will take priority and the check is needed to make sure it doesn't crash.
| @@ -11952,7 +11952,7 @@ TR::Register* | |||
| J9::Z::TreeEvaluator::VMinlineCompareAndSwap(TR::Node *node, TR::CodeGenerator *cg, TR::InstOpCode::Mnemonic casOp, bool isObj, bool isExchange) | |||
| { | |||
| TR::Register *scratchReg = NULL; | |||
| TR::Register *objReg, *oldVReg, *newVReg; | |||
| TR::Register *objReg, *oldVReg, *newVReg, *decompressedValueRegister; | |||
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I understand this exists, but we should initialize the registers here with NULL.
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I can change this.
| @@ -11969,9 +11969,10 @@ J9::Z::TreeEvaluator::VMinlineCompareAndSwap(TR::Node *node, TR::CodeGenerator * | |||
| // compression sequence. | |||
| bool isValueCompressedReference = false; | |||
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| TR::Node* decompressedValueNode = newVNode; | |||
| static bool UseOldCompareAndSwapObject = (bool)feGetEnv("TR_UseOldCompareAndSwapObject"); | |||
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I understand the intention was to match the environment set throughout the code base, but we should rename variable name useOldCompareAndSwapObject
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I can change this.
Added more comments to clarify issues. Renamed UseOldCompareAndSwapObject to useOldCompareAndSwapObject.
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My latest commit should address all previous comments. |
Disables code on Power and Z that hides compressedrefs logic from the fast path code generation for the following recognized methods:
sun_misc_Unsafe_compareAndSwapObject_jlObjectJjlObjectjlObject_Zjdk_internal_misc_Unsafe_compareAndExchangeObjectjdk_internal_misc_Unsafe_compareAndExchangeReferenceFast path code generation for those recognized methods is updated to handle compressedrefs.
Original behavior can be restored by setting the
TR_UseOldCompareAndSwapObjectenvironment variable. This behavior matches the X implementation which has already disabled the compressedrefs hiding logic when the envvar is not set.