JIT: more fixes for VN loop dependence tracking #56184

AndyAyersMS · 2021-07-22T20:53:04Z

Specify Overwrite when setting loop dependence map entries, as we may
refine the initial result.

Extract loop dependence of VNF_PhiMemoryDef.

Fixes new case noted in #55936, and 13/16 or so other cases Jakob sent
me privately. Also update a comment and fix tests to work better with
jitstress per other notes on that PR.

Specify `Overwrite` when setting loop dependence map entries, as we may refine the initial result. Fixes dotnet#56174. Extract loop dependence of `VNF_PhiMemoryDef`. Fixes new case noted in dotnet#55936, and 13/16 or so other cases Jakob sent me privately. Also update a comment and fix tests to work better with jitstress per other notes on that PR.

AndyAyersMS · 2021-07-22T20:53:23Z

cc @jakobbotsch @dotnet/jit-contrib

No spmi diffs.

briansull

Looks Good

AndyAyersMS · 2021-07-23T01:52:18Z

@jakobbotsch by my accounting this fixes all the test cases you sent me except for these 3:

11656046881568048475.cs
2692166044414030864.cs 
11738605779775786426.cs (hits jit assert)

The first two look like cases that should be handled by my fixes, so I will need to dig into them to see what is going wrong. In both cases the write/read sequence happens after a nested loop.

If a loop is removed (because of unrolling) then the loop dependence tracking introduced in dotnet#55936 and dotnet#56184 may not properly update. So when a loop is removed, walk up the chain of parent loops looking for one that is not removed, and record the dependence on that parent. Addresses last part of dotnet#54118.

…56436) If a loop is removed (because of unrolling) then the loop dependence tracking introduced in #55936 and #56184 may not properly update. So when a loop is removed, walk up the chain of parent loops looking for one that is not removed, and record the dependence on that parent. Addresses last part of #54118.

AndyAyersMS · 2021-07-28T20:23:31Z

The assert in that other test:

corerun.exe 11738605779775786426.exe

Assert failure(PID 20200 [0x00004ee8], Thread: 24136 [0x5e48]): Assertion failed 'i < BitSetTraits::GetSize(env)' 
   in 'Program:Main()' during 'Compute blocks reachability' (IL size 41)

AndyAyersMS · 2021-07-28T20:40:47Z

Looks like a flow opts bug, we end up not updating the pred list for BB08 properly and this ultimately leaves a dangling reference from BB07 to BB08 which causes the assert above.

*************** In fgUpdateFlowGraph()
Before updating the flow graph:

-----------------------------------------------------------------------------------------------------------------------------------------
BBnum BBid ref try hnd preds           weight    lp [IL range]     [jump]      [EH region]         [flags]
-----------------------------------------------------------------------------------------------------------------------------------------
BB01 [0000]  1                             1       [000..007)-> BB10 (always)                     i 
BB02 [0001]  1       BB10                  1       [007..00E)-> BB07 ( cond )                     i bwd bwd-target 
BB03 [0002]  1       BB02                  1       [00E..010)-> BB04 (always)                     keep i bwd 
BB04 [0009]  1       BB03                  1       [???..???)-> BB06 (always)                     i internal 
BB05 [0010]  0                             1       [???..???)-> BB09 (always)                     i internal 
BB06 [0003]  1       BB04                  1       [010..013)-> BB09 (always)                     keep i bwd 
BB07 [0004]  1       BB02                  1       [013..01A)-> BB09 ( cond )                     i bwd 
BB08 [0005]  1       BB07                  1       [01A..020)                                     i bwd 
BB09 [0006]  4       BB05,BB06,BB07,BB08   1       [020..024)                                     i bwd 
BB10 [0007]  2       BB01,BB09             1       [024..028)-> BB02 ( cond )                     i bwd 
BB11 [0008]  1       BB10                  1       [028..029)        (return)                     i 
-----------------------------------------------------------------------------------------------------------------------------------------


Removing unconditional jump to next block (BB03 -> BB04) (converted BB03 to fall-through)

Compacting blocks BB03 and BB04:
*************** In fgDebugCheckBBlist

Optimizing a jump to an unconditional jump (BB03 -> BB06 -> BB09)
Setting edge weights for BB03 -> BB09 to [0 .. 3.402823e+38]
fgRemoveBlock BB05

Removing unreachable BB05

Compacting blocks BB08 and BB09:
Second block has multiple incoming edges
Setting edge weights for BB03 -> BB08 to [0 .. 3.402823e+38]
Setting edge weights for BB06 -> BB08 to [0 .. 3.402823e+38]
*************** In fgDebugCheckBBlist

Moving BB07 after BB03 to enable reversal
New Basic Block BB12 [0011] created.
Setting edge weights for BB07 -> BB12 to [0 .. 3.402823e+38]

Reversing a conditional jump around an unconditional jump (BB02 -> BB07, BB03 -> BB08)
Setting edge weights for BB02 -> BB08 to [0 .. 3.402823e+38]

After reversing the jump:

-----------------------------------------------------------------------------------------------------------------------------------------
BBnum BBid ref try hnd preds           weight    lp [IL range]     [jump]      [EH region]         [flags]
-----------------------------------------------------------------------------------------------------------------------------------------
BB01 [0000]  1                             1       [000..007)-> BB10 (always)                     i 
BB02 [0001]  1       BB10                  1       [007..00E)-> BB08 ( cond )                     i bwd bwd-target 
BB07 [0004]  1       BB02                  1       [013..01A)-> BB08 ( cond )                     i bwd 
BB12 [0011]  1       BB07                  1       [???..???)-> BB08 (always)                     internal 
BB06 [0003]  0                             1       [010..013)-> BB08 (always)                     keep i bwd 
BB08 [0005]  4       BB02,BB06,BB12(2)     1       [01A..024)                                     i bwd 
BB10 [0007]  2       BB01,BB08             1       [024..028)-> BB02 ( cond )                     i bwd 
BB11 [0008]  1       BB10                  1       [028..029)        (return)                     i 
-----------------------------------------------------------------------------------------------------------------------------------------

AndyAyersMS · 2021-07-28T21:48:40Z

The bug is here:

runtime/src/coreclr/jit/fgopt.cpp

Lines 5620 to 5629 in eb1e55e

    
           // Add fall through fixup block, if needed. 
        
           // 
        
           if ((bDest->bbJumpKind == BBJ_NONE) || (bDest->bbJumpKind == BBJ_COND)) 
        
           { 
        
               BasicBlock* const bFixup = fgNewBBafter(BBJ_ALWAYS, bDest, true); 
        
               bFixup->inheritWeight(bDestNext); 
        
               bFixup->bbJumpDest = bDestNext; 
        
               fgReplacePred(bDestNext, bDest, bFixup); 
        
               fgAddRefPred(bFixup, bDest); 
        
           }

fgReplacePred will replace all pred uses, when we only wanted to replace one of them

Compacting blocks BB08 and BB09:
Second block has multiple incoming edges
Setting edge weights for BB03 -> BB08 to [0 .. 3.402823e+38]
Setting edge weights for BB06 -> BB08 to [0 .. 3.402823e+38]
*************** In fgDebugCheckBBlist

-----------------------------------------------------------------------------------------------------------------------------------------
BBnum BBid ref try hnd preds           weight    lp [IL range]     [jump]      [EH region]         [flags]
-----------------------------------------------------------------------------------------------------------------------------------------
BB01 [0000]  1                             1       [000..007)-> BB10 (always)                     i 
BB02 [0001]  1       BB10                  1       [007..00E)-> BB07 ( cond )                     i bwd bwd-target 
BB03 [0002]  1       BB02                  1       [00E..010)-> BB08 (always)                     keep i bwd 
BB06 [0003]  0                             1       [010..013)-> BB08 (always)                     keep i bwd 
BB07 [0004]  1       BB02                  1       [013..01A)-> BB08 ( cond )                     i bwd 
BB08 [0005]  4       BB03,BB06,BB07(2)     1       [01A..024)                                     i bwd 
BB10 [0007]  2       BB01,BB08             1       [024..028)-> BB02 ( cond )                     i bwd 
BB11 [0008]  1       BB10                  1       [028..029)        (return)                     i 
-----------------------------------------------------------------------------------------------------------------------------------------

Moving BB07 after BB03 to enable reversal
New Basic Block BB12 [0011] created.
Setting edge weights for BB07 -> BB12 to [0 .. 3.402823e+38]

-----------------------------------------------------------------------------------------------------------------------------------------
BBnum BBid ref try hnd preds           weight    lp [IL range]     [jump]      [EH region]         [flags]
-----------------------------------------------------------------------------------------------------------------------------------------
BB01 [0000]  1                             1       [000..007)-> BB10 (always)                     i 
BB02 [0001]  1       BB10                  1       [007..00E)-> BB07 ( cond )                     i bwd bwd-target 
BB03 [0002]  1       BB02                  1       [00E..010)-> BB08 (always)                     keep i bwd 
BB07 [0004]  1       BB02                  1       [013..01A)-> BB08 ( cond )                     i bwd 
BB12 [0011]  1       BB07                  1       [???..???)-> BB08 (always)                     internal 
BB06 [0003]  0                             1       [010..013)-> BB08 (always)                     keep i bwd 
BB08 [0005]  4       BB03,BB06,BB12(2)     1       [01A..024)                                     i bwd 
BB10 [0007]  2       BB01,BB08             1       [024..028)-> BB02 ( cond )                     i bwd 
BB11 [0008]  1       BB10                  1       [028..029)        (return)                     i 
-----------------------------------------------------------------------------------------------------------------------------------------

Reversing a conditional jump around an unconditional jump (BB02 -> BB07, BB03 -> BB08)
Setting edge weights for BB02 -> BB08 to [0 .. 3.402823e+38]

After reversing the jump:

-----------------------------------------------------------------------------------------------------------------------------------------
BBnum BBid ref try hnd preds           weight    lp [IL range]     [jump]      [EH region]         [flags]
-----------------------------------------------------------------------------------------------------------------------------------------
BB01 [0000]  1                             1       [000..007)-> BB10 (always)                     i 
BB02 [0001]  1       BB10                  1       [007..00E)-> BB08 ( cond )                     i bwd bwd-target 
BB07 [0004]  1       BB02                  1       [013..01A)-> BB08 ( cond )                     i bwd 
BB12 [0011]  1       BB07                  1       [???..???)-> BB08 (always)                     internal 
BB06 [0003]  0                             1       [010..013)-> BB08 (always)                     keep i bwd 
BB08 [0005]  4       BB02,BB06,BB12(2)     1       [01A..024)                                     i bwd 
BB10 [0007]  2       BB01,BB08             1       [024..028)-> BB02 ( cond )                     i bwd 
BB11 [0008]  1       BB10                  1       [028..029)        (return)                     i 
-----------------------------------------------------------------------------------------------------------------------------------------

This is new code that I added, I'll open a fresh issue for this...

dotnet-issue-labeler bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jul 22, 2021

AndyAyersMS mentioned this pull request Jul 22, 2021

JIT: track memory loop dependence of trees during value numbering #55936

Merged

BruceForstall approved these changes Jul 22, 2021

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briansull approved these changes Jul 22, 2021

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jakobbotsch approved these changes Jul 23, 2021

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AndyAyersMS merged commit b18ff29 into dotnet:main Jul 27, 2021

AndyAyersMS deleted the LoopMemoryDependenceVNFixes branch July 27, 2021 17:53

AndyAyersMS mentioned this pull request Jul 27, 2021

Test failure JIT/Performance/CodeQuality/Roslyn/CscBench/CscBench.sh #55162

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AndyAyersMS mentioned this pull request Jul 27, 2021

JIT: properly update loop memory dependence when loops are removed #56436

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AndyAyersMS mentioned this pull request Jul 28, 2021

JIT: flow opts does an incorrect pred list update #56495

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JIT: more fixes for VN loop dependence tracking #56184

JIT: more fixes for VN loop dependence tracking #56184

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JIT: more fixes for VN loop dependence tracking #56184

JIT: more fixes for VN loop dependence tracking #56184

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