Re-work fix for flow graph update. #40162
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In dotnet#39878 I switched fgUpdateChangedFlowGraph to call fgComputeReachability, which both removes unreachable blocks and calls fgComputeDoms. As mentioned in that PR, in addition to removing unreachable blocks fgRemoveUnreachableBlocks updates `BBF_LOOP_HEAD` flags even if no unreachable blocks were found. That resulted in some diffs, both positive and negative, from downstream effects: e.g., in some cases we now recognize more loops, which changes weights, etc. Some of the negative diffs affected benchmarks we are tracking, e.g., in dotnet#40094 `System.Text.RegularExpressions.Tests.Perf_Regex_Common` had a 10% regression because of codegen diffs in the large dynamic method created when compiling regular expressions. Because of these regressions, I decided to go with a more surgical fix for the original issue (assert when computing dominators after inlining GC polls). The downstream phases don't really need the dominator info so I changed fgUpdateChangedFlowGraph to not re-compute dominators after GC poll inlining. This reverses all diffs from dotnet#39878 and fixes dotnet#40094.
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@AndyAyersMS @dotnet/jit-contrib PTAL |
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| @@ -3722,7 +3726,8 @@ PhaseStatus Compiler::fgInsertGCPolls() | |||
| { | |||
| noway_assert(opts.OptimizationEnabled()); | |||
| fgReorderBlocks(); | |||
| fgUpdateChangedFlowGraph(); | |||
| constexpr bool computeDoms = false; | |||
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const would've worked too.
|
CopyCtorTest fails in other PRs as well, e.g., #40160. |
|
@erozenfeld Yes I've noticed that. I've just disabled the test on Mono, and have a PR out to fix it on X86. Sorry about that. |
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In dotnet#39878 I switched fgUpdateChangedFlowGraph to call fgComputeReachability, which both removes unreachable blocks and calls fgComputeDoms. As mentioned in that PR, in addition to removing unreachable blocks fgRemoveUnreachableBlocks updates `BBF_LOOP_HEAD` flags even if no unreachable blocks were found. That resulted in some diffs, both positive and negative, from downstream effects: e.g., in some cases we now recognize more loops, which changes weights, etc. Some of the negative diffs affected benchmarks we are tracking, e.g., in dotnet#40094 `System.Text.RegularExpressions.Tests.Perf_Regex_Common` had a 10% regression because of codegen diffs in the large dynamic method created when compiling regular expressions. Because of these regressions, I decided to go with a more surgical fix for the original issue (assert when computing dominators after inlining GC polls). The downstream phases don't really need the dominator info so I changed fgUpdateChangedFlowGraph to not re-compute dominators after GC poll inlining. This reverses all diffs from dotnet#39878 and fixes dotnet#40094.
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In #39878 I switched fgUpdateChangedFlowGraph to call fgComputeReachability,
which both removes unreachable blocks and calls fgComputeDoms. As mentioned
in that PR, in addition to removing unreachable blocks fgRemoveUnreachableBlocks
updates
BBF_LOOP_HEADflags even if no unreachable blocks were found. That resultedin some diffs, both positive and negative, from downstream effects: e.g., in some cases
we now recognize more loops, which changes weights, etc.
Some of the negative diffs affected benchmarks we are tracking, e.g., in #40094
System.Text.RegularExpressions.Tests.Perf_Regex_Commonhad a 10% regressionbecause of codegen diffs in the large dynamic method created when compiling regular expressions.
Because of these regressions, I decided to go with a more surgical fix for the original issue (assert when
computing dominators after inlining GC polls). The downstream phases don't really need the dominator
info so I changed fgUpdateChangedFlowGraph to not re-compute dominators after GC poll inlining.
This reverses all diffs from #39878 and fixes #40094.