cmd/compile: allow disable of PGO function value devirtualization with flag

Extend the pgodevirtualize debug flag to distinguish interface and
function devirtualization. Setting 1 keeps interface devirtualization
enabled but disables function value devirtualization.

For #64209.

Change-Id: I33aa7eb95ca0bdb215256d8c7cc8f9dac53ae30e
Reviewed-on: https://go-review.googlesource.com/c/go/+/543115
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/devirtualize/pgo.go b/src/cmd/compile/internal/devirtualize/pgo.go
index 7b6c8ba0c0..05b37d6be6 100644
--- a/src/cmd/compile/internal/devirtualize/pgo.go
+++ b/src/cmd/compile/internal/devirtualize/pgo.go
@@ -194,6 +194,10 @@ func ProfileGuided(fn *ir.Func, p *pgo.Profile) {
 // ir.Node if call was devirtualized, and if so also the callee and weight of
 // the devirtualized edge.
 func maybeDevirtualizeInterfaceCall(p *pgo.Profile, fn *ir.Func, call *ir.CallExpr) (ir.Node, *ir.Func, int64) {
+	if base.Debug.PGODevirtualize < 1 {
+		return nil, nil, 0
+	}
+
 	// Bail if we do not have a hot callee.
 	callee, weight := findHotConcreteInterfaceCallee(p, fn, call)
 	if callee == nil {
@@ -220,6 +224,10 @@ func maybeDevirtualizeInterfaceCall(p *pgo.Profile, fn *ir.Func, call *ir.CallEx
 // ir.Node if call was devirtualized, and if so also the callee and weight of
 // the devirtualized edge.
 func maybeDevirtualizeFunctionCall(p *pgo.Profile, fn *ir.Func, call *ir.CallExpr) (ir.Node, *ir.Func, int64) {
+	if base.Debug.PGODevirtualize < 2 {
+		return nil, nil, 0
+	}
+
 	// Bail if this is a direct call; no devirtualization necessary.
 	callee := pgo.DirectCallee(call.Fun)
 	if callee != nil {