RFR (XS): 8202952: C2: Unexpected dead nodes after matching
vladimir.kozlov at oracle.com
Tue Jan 22 20:42:11 UTC 2019
Got it. Good.
On 1/22/19 12:08 PM, Vladimir Ivanov wrote:
> On 22/01/2019 11:54, Vladimir Kozlov wrote:
>> The fix is different from what we discussed.
>> Can you explain how it helps?
> We discussed adding AddP case to _shared_nodes.
> Proposed fix achieves similar result with a different approach:
> * Matcher::clone_address_expressions() marks problematic AddP as shared (based on constant value);
> * DFA() doesn't construct duplicated State for inner AddP (since it's marked as shared);
> * Matcher doesn't need to materialize duplicated mach nodes, since it matches inner AddP separately;
> Best regards,
> Vladimir Ivanov
>> On 1/22/19 11:05 AM, Vladimir Ivanov wrote:
>>> The crash happens when PhaseCFG encounters a dead MachNode in the graph.
>>> The problematic node is a leftover from matching of an instruction with a duplicated memory operand (sarI_mem_CL 
>>> in that particular case).
>>> Address has the following shape :
>>> AddP (AddP DecodeN (LShiftL ConvI2L ConI)) ConL
>>> It could be subsumed into complex addressing expression, but the constant is too large (doesn't fit into immL32). So,
>>> matcher has to compute inner address expression separately and put it into a register.
>>> Since memory operand is duplicated, 2 copies are materialized during matching, but as part of ::Expand() one of the
>>> copies is eliminated, thus leaving a dead mach node in the IR (for the address expression).
>>> The fix is to adjust Matcher::clone_address_expressions() to avoid cloning inner AddP when constant offset is too large.
>>> Testing: hs-precheckin-comp, hs-tier1, hs-tier2
>>> Best regards,
>>> Vladimir Ivanov
>>>  instruct sarI_mem_CL(memory dst, rcx_RegI shift, rFlagsReg cr)
>>> match(Set dst (StoreI dst (RShiftI (LoadI dst) shift)));
>>> o347 AddP === _ o2181 o1768 o1769 [[o349 o371 ]]
>>> o1768 AddP === _ o2181 o2181 o1765 [[o347 ]]
>>> o2181 DecodeN === _ o287 [[o1768 o1768 o327 o347 o327 ]] #int[int:>=0]:NotNull:exact *
>>> o1765 LShiftL === _ o1761 o60 [[o1768 ]]
>>> o1761 ConvI2L === _ o1741 [[o1765 ]] #long:maxint-51..maxint-48
>>> o60 ConI === o0 [[o61 o1765 o1434 o2013 o1631 o2017 o1808 60 ]] #int:2
>>> o1769 ConL === o0 [[o347 ]] #long:-8589932784
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