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cmd/compile: keep pointer input arguments live throughout function

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Introduce a KeepAlive op which makes sure that its argument is kept
live until the KeepAlive.  Use KeepAlive to mark pointer input
arguments as live after each function call and at each return.

We do this change only for pointer arguments.  Those are the
critical ones to handle because they might have finalizers.
Doing compound arguments (slices, structs, ...) is more complicated
because we would need to track field liveness individually (we do
that for auto variables now, but inputs requires extra trickery).

Turn off the automatic marking of args as live.  That way, when args
are explicitly nulled, plive will know that the original argument is
dead.

The KeepAlive op will be the eventual implementation of
runtime.KeepAlive.

Fixes #15277

Change-Id: I5f223e65d99c9f8342c03fbb1512c4d363e903e5
Reviewed-on: https://go-review.googlesource.com/22365
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
This commit is contained in:
Keith Randall 2016-04-21 19:28:28 -07:00
parent d52022676d
commit 3572c6418b
10 changed files with 145 additions and 34 deletions
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12
src/cmd/compile/internal/amd64/ssa.go
View file

@ -878,6 +878,18 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
gc.Gvarkill(v.Aux.(*gc.Node))
case ssa.OpVarLive:
gc.Gvarlive(v.Aux.(*gc.Node))
case ssa.OpKeepAlive:
if !v.Args[0].Type.IsPtrShaped() {
v.Fatalf("keeping non-pointer alive %v", v.Args[0])
}
n, off := gc.AutoVar(v.Args[0])
if n == nil {
v.Fatalf("KeepLive with non-spilled value %s %s", v, v.Args[0])
}
if off != 0 {
v.Fatalf("KeepLive with non-zero offset spill location %s:%d", n, off)
}
gc.Gvarlive(n)
case ssa.OpAMD64LoweredNilCheck:
// Optimization - if the subsequent block has a load or store
// at the same address, we don't need to issue this instruction.