cmd/compile: avoid excessive libfuzzer instrumentation of int compares

Do not intercept integer compares that are used to increment libFuzzer's
8-bit counters. This is unnecessary and has a negative impact on the
fuzzing performance. This fixes #53760.

Change-Id: Id22efac968b18014eedabb6f0762e1456897024e
GitHub-Last-Rev: 52f69fd
GitHub-Pull-Request: #53786
Reviewed-on: https://go-review.googlesource.com/c/go/+/416796
Run-TryBot: Keith Randall <[email protected]>
Auto-Submit: Keith Randall <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Matthew Dempsky <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: kyakdan

src/cmd/compile/internal/walk/compare.go

@@ -116,7 +116,7 @@ func walkCompare(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
 
 	switch t.Kind() {
 	default:
-		if base.Debug.Libfuzzer != 0 && t.IsInteger() {
+		if base.Debug.Libfuzzer != 0 && t.IsInteger() && (n.X.Name() == nil || !n.X.Name().Libfuzzer8BitCounter()) {
 			n.X = cheapExpr(n.X, init)
 			n.Y = cheapExpr(n.Y, init)