[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>

1 files changed, 2 insertions, 2 deletions

diff --git a/test/nosplit.go b/test/nosplit.go
index e7c00f5783..e5c2a9f30e 100644
--- a/test/nosplit.go
+++ b/test/nosplit.go
@@ -285,12 +285,12 @@ TestCases:
 				// 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
 						}
 					}
 				}