Josh Bleecher Snyder dffe5ac9f2 cmd/compile: eliminate dead code in if statements after typechecking ... This is a more thorough and cleaner fix than doing dead code elimination separately during inlining, escape analysis, and export. Unfortunately, it does add another full walk of the AST. The performance impact is very small, but not non-zero. If a label or goto is present in the dead code, it is not eliminated. This restriction can be removed once label/goto checking occurs much earlier in the compiler. In practice, it probably doesn't matter much. Updates #19699 Fixes #19705 name old alloc/op new alloc/op delta Template 39.2MB ± 0% 39.3MB ± 0% +0.28% (p=0.008 n=5+5) Unicode 29.8MB ± 0% 29.8MB ± 0% ~ (p=1.000 n=5+5) GoTypes 113MB ± 0% 113MB ± 0% -0.55% (p=0.008 n=5+5) SSA 1.25GB ± 0% 1.25GB ± 0% +0.02% (p=0.008 n=5+5) Flate 25.3MB ± 0% 25.3MB ± 0% -0.24% (p=0.032 n=5+5) GoParser 31.7MB ± 0% 31.8MB ± 0% +0.31% (p=0.008 n=5+5) Reflect 78.2MB ± 0% 78.3MB ± 0% ~ (p=0.421 n=5+5) Tar 26.6MB ± 0% 26.7MB ± 0% +0.21% (p=0.008 n=5+5) XML 42.2MB ± 0% 42.2MB ± 0% ~ (p=0.056 n=5+5) name old allocs/op new allocs/op delta Template 385k ± 0% 387k ± 0% +0.51% (p=0.016 n=5+5) Unicode 321k ± 0% 321k ± 0% ~ (p=1.000 n=5+5) GoTypes 1.14M ± 0% 1.14M ± 0% ~ (p=1.000 n=5+5) SSA 9.71M ± 0% 9.72M ± 0% +0.10% (p=0.008 n=5+5) Flate 234k ± 1% 234k ± 1% ~ (p=0.690 n=5+5) GoParser 315k ± 0% 317k ± 0% +0.71% (p=0.008 n=5+5) Reflect 980k ± 0% 983k ± 0% +0.30% (p=0.032 n=5+5) Tar 251k ± 0% 252k ± 0% +0.55% (p=0.016 n=5+5) XML 392k ± 0% 393k ± 0% +0.30% (p=0.008 n=5+5) Change-Id: Ia10ff4bbf5c6eae782582cc9cbc9785494d4fb83 Reviewed-on: https://go-review.googlesource.com/38773 Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com> Reviewed-by: Matthew Dempsky <mdempsky@google.com>		2017-04-18 17:13:30 +00:00
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