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[dev.ssa] cmd/compile: Use varkill only for non-SSAable vars

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For variables which get SSA'd, SSA keeps track of all the def/kill.
It is only for on-stack variables that we need them.

This reduces stack frame sizes significantly because often the
only use of a variable was a varkill, and without that last use
the variable doesn't get allocated in the frame at all.

Fixes #12602

Change-Id: I3f00a768aa5ddd8d7772f375b25f846086a3e689
Reviewed-on: https://go-review.googlesource.com/14758
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Keith Randall 2015-09-19 12:01:39 -07:00
parent 37590bddc4
commit d29e92be52
4 changed files with 7 additions and 5 deletions
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4
src/cmd/compile/internal/gc/ssa.go
View File

@ -794,7 +794,9 @@ func (s *state) stmt(n *Node) {
// We only care about liveness info at call sites, so putting the // We only care about liveness info at call sites, so putting the
// varkill in the store chain is enough to keep it correctly ordered // varkill in the store chain is enough to keep it correctly ordered
// with respect to call ops. // with respect to call ops.
s.vars[&memVar] = s.newValue1A(ssa.OpVarKill, ssa.TypeMem, n.Left, s.mem()) if !canSSA(n.Left) {
s.vars[&memVar] = s.newValue1A(ssa.OpVarKill, ssa.TypeMem, n.Left, s.mem())
}
case OCHECKNIL: case OCHECKNIL:
p := s.expr(n.Left) p := s.expr(n.Left)

2
src/cmd/internal/obj/stack.go
View File

@ -41,7 +41,7 @@ const (
STACKSYSTEM = 0 STACKSYSTEM = 0
StackSystem = STACKSYSTEM StackSystem = STACKSYSTEM
StackBig = 4096 StackBig = 4096
StackGuard = 960*stackGuardMultiplier + StackSystem StackGuard = 640*stackGuardMultiplier + StackSystem
StackSmall = 128 StackSmall = 128
StackLimit = StackGuard - StackSystem - StackSmall StackLimit = StackGuard - StackSystem - StackSmall
) )

2
src/runtime/stack2.go
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@ -86,7 +86,7 @@ const (
// The stack guard is a pointer this many bytes above the // The stack guard is a pointer this many bytes above the
// bottom of the stack. // bottom of the stack.
_StackGuard = 960*stackGuardMultiplier + _StackSystem _StackGuard = 640*stackGuardMultiplier + _StackSystem
// After a stack split check the SP is allowed to be this // After a stack split check the SP is allowed to be this
// many bytes below the stack guard. This saves an instruction // many bytes below the stack guard. This saves an instruction

4
test/nosplit.go
View File

@ -285,12 +285,12 @@ TestCases:
// Instead of rewriting the test cases above, adjust // Instead of rewriting the test cases above, adjust
// the first stack frame to use up the extra bytes. // the first stack frame to use up the extra bytes.
if i == 0 { if i == 0 {
size += 832 - 128 size += 512 - 128
// Noopt builds have a larger stackguard. // Noopt builds have a larger stackguard.
// See ../cmd/dist/buildruntime.go:stackGuardMultiplier // See ../cmd/dist/buildruntime.go:stackGuardMultiplier
for _, s := range strings.Split(os.Getenv("GO_GCFLAGS"), " ") { for _, s := range strings.Split(os.Getenv("GO_GCFLAGS"), " ") {
if s == "-N" { if s == "-N" {
size += 960 size += 640
} }
} }
} }