cmd/compile/internal: small tweak to merge locals trace output

For -gcflags=-d=mergelocalstrace=1 (which reports estimated savings
from stack slot merging), emit separate values for pointerful vs
non-pointerful variables, for a bit more detail.

Updates #62737.
Updates #65532.
Updates #65495.

Change-Id: I9dd27d2a254036448c85c13d189d1ed36157c9d7
Reviewed-on: https://go-review.googlesource.com/c/go/+/576680
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

Author: thanm

src/cmd/compile/internal/liveness/mergelocals.go

@@ -139,16 +139,22 @@ func (mls *MergeLocalsState) Followers(n *ir.Name, tmp []*ir.Name) []*ir.Name {
 	return tmp
 }
 
-// EstSavings returns the estimated reduction in stack size for
-// the given merge locals state.
-func (mls *MergeLocalsState) EstSavings() int {
-	tot := 0
+// EstSavings returns the estimated reduction in stack size (number of bytes) for
+// the given merge locals state via a pair of ints, the first for non-pointer types and the second for pointer types.
+func (mls *MergeLocalsState) EstSavings() (int, int) {
+	totnp := 0
+	totp := 0
 	for n := range mls.partition {
 		if mls.Subsumed(n) {
-			tot += int(n.Type().Size())
+			sz := int(n.Type().Size())
+			if n.Type().HasPointers() {
+				totp += sz
+			} else {
+				totnp += sz
+			}
 		}
 	}
-	return tot
+	return totnp, totp
 }
 
 // check tests for various inconsistencies and problems in mls,

src/cmd/compile/internal/ssagen/pgen.go

@@ -155,8 +155,9 @@ func (s *ssafn) AllocFrame(f *ssa.Func) {
 	var mls *liveness.MergeLocalsState
 	if base.Debug.MergeLocals != 0 {
 		mls = liveness.MergeLocals(fn, f)
-		if base.Debug.MergeLocalsTrace == 1 && mls != nil {
-			fmt.Fprintf(os.Stderr, "%s: %d bytes of stack space saved via stack slot merging\n", ir.FuncName(fn), mls.EstSavings())
+		if base.Debug.MergeLocalsTrace > 0 && mls != nil {
+			savedNP, savedP := mls.EstSavings()
+			fmt.Fprintf(os.Stderr, "%s: %d bytes of stack space saved via stack slot merging (%d nonpointer %d pointer)\n", ir.FuncName(fn), savedNP+savedP, savedNP, savedP)
 			if base.Debug.MergeLocalsTrace > 1 {
 				fmt.Fprintf(os.Stderr, "=-= merge locals state for %v:\n%v",
 					fn, mls)