cmd/compile: manage Slot array better

steals idea from CL 312093

further investigation revealed additional duplicate
slots (equivalent, but not equal), so delete those too.

Rearranged Func.Names to be addresses of slots,
create canonical addresses so that split slots
(which use those addresses to refer to their parent,
and split slots can be further split)
will preserve "equivalent slots are equal".

Removes duplicates, improves metrics for "args at entry".

Change-Id: I5bbdcb50bd33655abcab3d27ad8cdce25499faaf
Reviewed-on: https://go-review.googlesource.com/c/go/+/312292
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/ssa/stackalloc.go b/src/cmd/compile/internal/ssa/stackalloc.go
index d962579122..d41f3996af 100644
--- a/src/cmd/compile/internal/ssa/stackalloc.go
+++ b/src/cmd/compile/internal/ssa/stackalloc.go
@@ -141,10 +141,11 @@ func (s *stackAllocState) stackalloc() {
 		s.names = make([]LocalSlot, n)
 	}
 	names := s.names
+	empty := LocalSlot{}
 	for _, name := range f.Names {
 		// Note: not "range f.NamedValues" above, because
 		// that would be nondeterministic.
-		for _, v := range f.NamedValues[name] {
+		for _, v := range f.NamedValues[*name] {
 			if v.Op == OpArgIntReg || v.Op == OpArgFloatReg {
 				aux := v.Aux.(*AuxNameOffset)
 				// Never let an arg be bound to a differently named thing.
@@ -162,10 +163,12 @@ func (s *stackAllocState) stackalloc() {
 				continue
 			}
 
-			if f.pass.debug > stackDebug {
-				fmt.Printf("stackalloc value %s to name %s\n", v, name)
+			if names[v.ID] == empty {
+				if f.pass.debug > stackDebug {
+					fmt.Printf("stackalloc value %s to name %s\n", v, *name)
+				}
+				names[v.ID] = *name
 			}
-			names[v.ID] = name
 		}
 	}