cmd/compile: enable constant-time CFG editing
Provide indexes along with block pointers for Preds
and Succs arrays. This allows us to splice edges in
and out of those arrays in constant time.
Fixes worst-case O(n^2) behavior in deadcode and fuse.
benchmark old ns/op new ns/op delta
BenchmarkFuse1-8 2065 2057 -0.39%
BenchmarkFuse10-8 9408 9073 -3.56%
BenchmarkFuse100-8 105238 76277 -27.52%
BenchmarkFuse1000-8 3982562 1026750 -74.22%
BenchmarkFuse10000-8 301220329 12824005 -95.74%
BenchmarkDeadCode1-8 1588 1566 -1.39%
BenchmarkDeadCode10-8 4333 4250 -1.92%
BenchmarkDeadCode100-8 32031 32574 +1.70%
BenchmarkDeadCode1000-8 590407 468275 -20.69%
BenchmarkDeadCode10000-8 17822890 5000818 -71.94%
BenchmarkDeadCode100000-8 1388706640 78021127 -94.38%
BenchmarkDeadCode200000-8 5372518479 168598762 -96.86%
Change-Id: Iccabdbb9343fd1c921ba07bbf673330a1c36ee17
Reviewed-on: https://go-review.googlesource.com/22589
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index 311d5b8..c702919 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -9777,8 +9777,7 @@
next := b.Succs[0]
b.Kind = BlockPlain
b.SetControl(nil)
- b.Succs[0] = next
- b.Likely = BranchUnknown
+ _ = next
return true
}
case BlockIf:
@@ -9795,9 +9794,9 @@
no := b.Succs[1]
b.Kind = BlockIf
b.SetControl(cond)
- b.Succs[0] = no
- b.Succs[1] = yes
- b.Likely *= -1
+ b.swapSuccessors()
+ _ = no
+ _ = yes
return true
}
// match: (If (ConstBool [c]) yes no)
@@ -9816,8 +9815,8 @@
}
b.Kind = BlockFirst
b.SetControl(nil)
- b.Succs[0] = yes
- b.Succs[1] = no
+ _ = yes
+ _ = no
return true
}
// match: (If (ConstBool [c]) yes no)
@@ -9836,9 +9835,9 @@
}
b.Kind = BlockFirst
b.SetControl(nil)
- b.Succs[0] = no
- b.Succs[1] = yes
- b.Likely *= -1
+ b.swapSuccessors()
+ _ = no
+ _ = yes
return true
}
}
