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[dev.ssa] cmd/compile: schedule values dependent on the control later

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To reduce the number of spills, give any non-phi values whose argument
is the control the same priority as the control.

With mask.bash, this reduces regenerated flags from 603 to 240.

Change-Id: I26883d69e80357c56b343428fb528102b3f26e7a
Reviewed-on: https://go-review.googlesource.com/14042
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Todd Neal 2015-08-29 12:51:04 -05:00
parent 3b7f0c9cba
commit 21e6a055c1
1 changed files with 15 additions and 3 deletions
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18
src/cmd/compile/internal/ssa/schedule.go
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@ -89,9 +89,21 @@ func schedule(f *Func) {
// Force the control value to be scheduled at the end,
// unless it is a phi value (which must be first).
score[b.Control.ID] = 4
// TODO: some times control values are used by other values
// in the block. So the control value will not appear at
// the very end. Decide if this is a problem or not.
// Schedule values dependent on the control value at the end.
// This reduces the number of register spills. We don't find
// all values that depend on the control, just values with a
// direct dependency. This is cheaper and in testing there
// was no difference in the number of spills.
for _, v := range b.Values {
if v.Op != OpPhi {
for _, a := range v.Args {
if a == b.Control {
score[v.ID] = 4
}
}
}
}
}
// Initialize priority queue with schedulable values.