[dev.ssa] cmd/compile: Use varkill only for non-SSAable vars
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>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 8e0f0dc..6cb5c57 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -794,7 +794,9 @@
// We only care about liveness info at call sites, so putting the
// varkill in the store chain is enough to keep it correctly ordered
// 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:
p := s.expr(n.Left)
diff --git a/src/cmd/internal/obj/stack.go b/src/cmd/internal/obj/stack.go
index b1630b5..87698b3 100644
--- a/src/cmd/internal/obj/stack.go
+++ b/src/cmd/internal/obj/stack.go
@@ -41,7 +41,7 @@
STACKSYSTEM = 0
StackSystem = STACKSYSTEM
StackBig = 4096
- StackGuard = 960*stackGuardMultiplier + StackSystem
+ StackGuard = 640*stackGuardMultiplier + StackSystem
StackSmall = 128
StackLimit = StackGuard - StackSystem - StackSmall
)
diff --git a/src/runtime/stack2.go b/src/runtime/stack2.go
index 02b82eb..59d4ef6 100644
--- a/src/runtime/stack2.go
+++ b/src/runtime/stack2.go
@@ -86,7 +86,7 @@
// The stack guard is a pointer this many bytes above the
// bottom of the stack.
- _StackGuard = 960*stackGuardMultiplier + _StackSystem
+ _StackGuard = 640*stackGuardMultiplier + _StackSystem
// After a stack split check the SP is allowed to be this
// many bytes below the stack guard. This saves an instruction
diff --git a/test/nosplit.go b/test/nosplit.go
index e7c00f5..e5c2a9f 100644
--- a/test/nosplit.go
+++ b/test/nosplit.go
@@ -285,12 +285,12 @@
// Instead of rewriting the test cases above, adjust
// the first stack frame to use up the extra bytes.
if i == 0 {
- size += 832 - 128
+ size += 512 - 128
// Noopt builds have a larger stackguard.
// See ../cmd/dist/buildruntime.go:stackGuardMultiplier
for _, s := range strings.Split(os.Getenv("GO_GCFLAGS"), " ") {
if s == "-N" {
- size += 960
+ size += 640
}
}
}
