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runtime: short path for equal pointers in arm64 memequal
If memequal is invoked with the same pointers as arguments it ends up comparing the whole memory contents, instead of just comparing the pointers. This effectively makes an operation that could be O(1) into O(n). All the other architectures already have this optimization in place. For instance, arm64 also have it, in memequal_varlen. Such optimization is very specific, one case that it will probably benefit is programs that rely heavily on interning of strings. goos: darwin goarch: arm64 pkg: bytes │ old.txt │ new.txt │ │ sec/op │ sec/op vs base │ Equal/same/1-8 2.678n ± ∞ ¹ 2.400n ± ∞ ¹ -10.38% (p=0.008 n=5) Equal/same/6-8 3.267n ± ∞ ¹ 2.431n ± ∞ ¹ -25.59% (p=0.008 n=5) Equal/same/9-8 2.981n ± ∞ ¹ 2.385n ± ∞ ¹ -19.99% (p=0.008 n=5) Equal/same/15-8 2.974n ± ∞ ¹ 2.390n ± ∞ ¹ -19.64% (p=0.008 n=5) Equal/same/16-8 2.983n ± ∞ ¹ 2.380n ± ∞ ¹ -20.21% (p=0.008 n=5) Equal/same/20-8 3.567n ± ∞ ¹ 2.384n ± ∞ ¹ -33.17% (p=0.008 n=5) Equal/same/32-8 3.568n ± ∞ ¹ 2.385n ± ∞ ¹ -33.16% (p=0.008 n=5) Equal/same/4K-8 78.040n ± ∞ ¹ 2.378n ± ∞ ¹ -96.95% (p=0.008 n=5) Equal/same/4M-8 78713.000n ± ∞ ¹ 2.385n ± ∞ ¹ -100.00% (p=0.008 n=5) Equal/same/64M-8 1348095.000n ± ∞ ¹ 2.381n ± ∞ ¹ -100.00% (p=0.008 n=5) geomean 43.52n 2.390n -94.51% ¹ need >= 6 samples for confidence interval at level 0.95 │ old.txt │ new.txt │ │ B/s │ B/s vs base │ Equal/same/1-8 356.1Mi ± ∞ ¹ 397.3Mi ± ∞ ¹ +11.57% (p=0.008 n=5) Equal/same/6-8 1.711Gi ± ∞ ¹ 2.298Gi ± ∞ ¹ +34.35% (p=0.008 n=5) Equal/same/9-8 2.812Gi ± ∞ ¹ 3.515Gi ± ∞ ¹ +24.99% (p=0.008 n=5) Equal/same/15-8 4.698Gi ± ∞ ¹ 5.844Gi ± ∞ ¹ +24.41% (p=0.008 n=5) Equal/same/16-8 4.995Gi ± ∞ ¹ 6.260Gi ± ∞ ¹ +25.34% (p=0.008 n=5) Equal/same/20-8 5.222Gi ± ∞ ¹ 7.814Gi ± ∞ ¹ +49.63% (p=0.008 n=5) Equal/same/32-8 8.353Gi ± ∞ ¹ 12.496Gi ± ∞ ¹ +49.59% (p=0.008 n=5) Equal/same/4K-8 48.88Gi ± ∞ ¹ 1603.96Gi ± ∞ ¹ +3181.17% (p=0.008 n=5) Equal/same/4M-8 49.63Gi ± ∞ ¹ 1637911.85Gi ± ∞ ¹ +3300381.91% (p=0.008 n=5) Equal/same/64M-8 46.36Gi ± ∞ ¹ 26253069.97Gi ± ∞ ¹ +56626517.99% (p=0.008 n=5) geomean 6.737Gi 122.7Gi +1721.01% ¹ need >= 6 samples for confidence interval at level 0.95 Fixes golang#64381 Change-Id: I7d423930a688edd88c4ba60d45e097296d9be852 GitHub-Last-Rev: ae8189f GitHub-Pull-Request: golang#64419 Reviewed-on: https://go-review.googlesource.com/c/go/+/545416 TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> Run-TryBot: Cherry Mui <cherryyz@google.com>
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