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[dev.ssa] cmd/compile: optimization for && and || expressions

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Compiling && and || expressions often leads to control
flow of the following form:

p:
  If a goto b else c
b: <- p ...
  x = phi(a, ...)
  If x goto t else u

Note that if we take the edge p->b, then we are guaranteed
to take the edge b->t also.  So in this situation, we might
as well go directly from p to t.

Change-Id: I6974f1e6367119a2ddf2014f9741fdb490edcc12
Reviewed-on: https://go-review.googlesource.com/18910
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
Keith Randall 2016-01-25 09:21:17 -08:00
parent 9d6e605cf7
commit d8a65672f8
4 changed files with 208 additions and 18 deletions
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1
src/cmd/compile/internal/ssa/compile.go
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@ -89,6 +89,7 @@ var passes = [...]pass{
{"early phielim", phielim, false},
{"early copyelim", copyelim, false},
{"early deadcode", deadcode, false}, // remove generated dead code to avoid doing pointless work during opt
{"short circuit", shortcircuit, false},
{"decompose", decompose, true},
{"opt", opt, true}, // TODO: split required rules and optimizing rules
{"opt deadcode", deadcode, false}, // remove any blocks orphaned during opt