JIT: Remove Compiler::fgConnectFallThrough and BBJ_COND fix-ups in loop phases #97191
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ghost
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch Issue DetailsNext step for #93020. This removes the implicit fallthrough invariant for
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jakobbotsch
reviewed
Jan 19, 2024
| @@ -4988,7 +4987,7 @@ bool FlowGraphNaturalLoop::AnalyzeIteration(NaturalLoopIterInfo* info) | |||
| return false; | |||
| } | |||
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| assert(ContainsBlock(cond->GetTrueTarget()) != ContainsBlock(cond->GetFalseTarget())); | |||
| // assert(ContainsBlock(cond->GetTrueTarget()) != ContainsBlock(cond->GetFalseTarget())); | |||
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This is a correctness issue, but I have a local change that should make things work out even with your change here. Hopefully I'll get that in early next week.
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Thanks! No rush on that
3 tasks
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cc @dotnet/jit-contrib. I'm going to hold off on requesting reviews until I merge in the fix Jakob mentioned above. Diffs are pretty noisy -- lots of size improvements and regressions. I suspect we are encountering more false branches that don't fall through by the time we get to block reordering, creating more opportunities for behavioral diffs. |
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/azp run runtime-coreclr jitstress, runtime-coreclr libraries-jitstress, runtime-coreclr outerloop, Fuzzlyn |
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Azure Pipelines successfully started running 4 pipeline(s). |
This was referenced Jan 19, 2024
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/azp run runtime-coreclr jitstress, runtime-coreclr libraries-jitstress, runtime-coreclr outerloop, Fuzzlyn |
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Azure Pipelines successfully started running 4 pipeline(s). |
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/azp run runtime-coreclr jitstress, runtime-coreclr libraries-jitstress, runtime-coreclr outerloop, Fuzzlyn |
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Azure Pipelines successfully started running 4 pipeline(s). |
Diff results for #97191Assembly diffsAssembly diffs for linux/arm64 ran on windows/x64Diffs are based on 2,501,660 contexts (1,003,806 MinOpts, 1,497,854 FullOpts). MISSED contexts: base: 3,546 (0.14%), diff: 3,557 (0.14%) Overall (-126,148 bytes)
FullOpts (-126,148 bytes)
Assembly diffs for linux/x64 ran on windows/x64Diffs are based on 2,595,038 contexts (1,052,329 MinOpts, 1,542,709 FullOpts). MISSED contexts: base: 3,596 (0.14%), diff: 3,597 (0.14%) Overall (-208,870 bytes)
FullOpts (-208,870 bytes)
Assembly diffs for osx/arm64 ran on windows/x64Diffs are based on 2,263,021 contexts (930,876 MinOpts, 1,332,145 FullOpts). MISSED contexts: base: 2,925 (0.13%), diff: 2,944 (0.13%) Overall (-97,340 bytes)
FullOpts (-97,340 bytes)
Assembly diffs for windows/arm64 ran on windows/x64Diffs are based on 2,318,299 contexts (931,543 MinOpts, 1,386,756 FullOpts). MISSED contexts: base: 2,587 (0.11%), diff: 2,595 (0.11%) Overall (-117,288 bytes)
FullOpts (-117,288 bytes)
Assembly diffs for windows/x64 ran on windows/x64Diffs are based on 2,492,951 contexts (983,689 MinOpts, 1,509,262 FullOpts). MISSED contexts: base: 3,859 (0.15%), diff: 3,860 (0.15%) Overall (-150,214 bytes)
FullOpts (-150,214 bytes)
Details here Assembly diffs for linux/arm ran on windows/x86Diffs are based on 2,238,225 contexts (827,812 MinOpts, 1,410,413 FullOpts). MISSED contexts: base: 74,052 (3.20%), diff: 74,053 (3.20%) Overall (-72,938 bytes)
FullOpts (-72,938 bytes)
Assembly diffs for windows/x86 ran on windows/x86Diffs are based on 2,297,926 contexts (841,817 MinOpts, 1,456,109 FullOpts). MISSED contexts: base: 2,090 (0.09%), diff: 3,444 (0.15%) Overall (-179,094 bytes)
FullOpts (-179,094 bytes)
Details here Throughput diffsThroughput diffs for linux/arm64 ran on linux/x64Overall (-0.39% to -0.12%)
FullOpts (-0.52% to -0.16%)
Throughput diffs for linux/x64 ran on linux/x64Overall (-0.42% to -0.14%)
FullOpts (-0.54% to -0.19%)
Details here Throughput diffs for linux/arm ran on windows/x86Overall (-0.49% to -0.07%)
MinOpts (+0.02% to +0.06%)
FullOpts (-0.49% to -0.07%)
Throughput diffs for windows/x86 ran on windows/x86Overall (-0.31% to -0.09%)
MinOpts (+0.03% to +0.10%)
FullOpts (-0.33% to -0.09%)
Details here Throughput diffs for linux/arm64 ran on windows/x64Overall (-0.35% to -0.11%)
MinOpts (-0.01% to -0.00%)
FullOpts (-0.48% to -0.13%)
Throughput diffs for linux/x64 ran on windows/x64Overall (-0.37% to -0.13%)
MinOpts (-0.01% to +0.00%)
FullOpts (-0.48% to -0.15%)
Throughput diffs for osx/arm64 ran on windows/x64Overall (-0.36% to -0.11%)
MinOpts (-0.01% to +0.00%)
FullOpts (-0.47% to -0.13%)
Throughput diffs for windows/arm64 ran on windows/x64Overall (-0.38% to -0.12%)
MinOpts (-0.01% to +0.00%)
FullOpts (-0.49% to -0.13%)
Throughput diffs for windows/x64 ran on windows/x64Overall (-0.45% to -0.14%)
MinOpts (-0.01% to -0.00%)
FullOpts (-0.51% to -0.15%)
Details here |
Diff results for #97191Throughput diffsThroughput diffs for linux/arm64 ran on linux/x64Overall (-0.34% to -0.10%)
FullOpts (-0.45% to -0.12%)
Throughput diffs for linux/x64 ran on linux/x64Overall (-0.35% to -0.12%)
FullOpts (-0.46% to -0.14%)
Details here |
Diff results for #97191Throughput diffsThroughput diffs for linux/arm64 ran on linux/x64Overall (-0.34% to -0.10%)
FullOpts (-0.45% to -0.12%)
Throughput diffs for linux/x64 ran on linux/x64Overall (-0.35% to -0.12%)
FullOpts (-0.46% to -0.14%)
Details here |
jakobbotsch
reviewed
Jan 23, 2024
Comment on lines
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| // Block layout should not change at this point. | ||
| // Do one last pass to reverse any conditions that might yield more fall-through branches. | ||
| if (opts.OptimizationEnabled()) | ||
| { | ||
| for (BasicBlock* const block : Blocks()) | ||
| { | ||
| if (block->KindIs(BBJ_COND) && block->CanRemoveJumpToTarget(block->GetTrueTarget(), this)) | ||
| { | ||
| // Reverse the jump condition | ||
| GenTree* test = block->lastNode(); | ||
| assert(test->OperIsConditionalJump()); | ||
| GenTree* cond = gtReverseCond(test); | ||
| assert(cond == test); // Ensure `gtReverseCond` did not create a new node. | ||
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| BasicBlock* newFalseTarget = block->GetTrueTarget(); | ||
| BasicBlock* newTrueTarget = block->GetFalseTarget(); | ||
| block->SetTrueTarget(newTrueTarget); | ||
| block->SetFalseTarget(newFalseTarget); | ||
| assert(block->CanRemoveJumpToTarget(newFalseTarget, this)); | ||
| } | ||
| } | ||
| } |
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This should be a proper phase ensuring post-phase checks run, and ensuring the changed IR nodes are dumped.
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I was planning on removing this change from this PR, and possibly introducing it if/when we remove the condition reversals done in earlier phases. I'll add it as a new phase then.
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Sounds good... sorry about the draft review.
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No worries! I appreciate the feedback -- this should be ready soon.
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this should be ready soon.
Famous last words... closing this in favor of #97488.
This was referenced Jan 23, 2024
amanasifkhalid
added a commit
that referenced
this pull request
Jan 29, 2024
Part of #93020. This change adds back in most of #97191 and #96609, except for any significant changes to the flowgraph optimization passes to reduce churn. With this change, the false target of a BBJ_COND can diverge from the next block until Compiler::optOptimizeLayout, in which we reestablish implicit fall-through with fgConnectFallThrough to preserve the existing block reordering behavior. Note that the deferral of these fall-through fixups causes diffs in the edge weights, which can alter the behavior of fgReorderBlocks, hence some of the size regressions
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Next step for #93020. This removes the implicit fallthrough invariant for
bbFalseTarget(as well as the corresponding logic for maintaining that invariant) from the loop representation. At this point, I noticed we can get rid ofCompiler::fgConnectFallThrough, so I thought I'd include that in this change. There's still some cruft left in earlier phases for fixing up fallthrough into the false target withBBJ_ALWAYSblocks, but this PR is big enough -- I'll save the remaining cleanup for a follow-up PR.