cmd/compile: add -d=inlstaticinit debug flag

This CL adds -d=inlstaticinit to control whether static initialization
of inlined function calls (added in CL 450136) is allowed.

We've needed to fix it once already (CL 451555) and Google-internal
testing is hitting additional failure cases, so putting this
optimization behind a feature flag seems appropriate regardless.

Also, while we diagnose and fix the remaining cases, this CL also
disables the optimization to avoid miscompilations.

Updates #56894.

Change-Id: If52a358ad1e9d6aad1c74fac5a81ff9cfa5a3793
Reviewed-on: https://go-review.googlesource.com/c/go/+/452676
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/base/debug.go

@@ -31,6 +31,7 @@ type DebugFlags struct {
 	GCProg                int    `help:"print dump of GC programs"`
 	Gossahash             string `help:"hash value for use in debugging the compiler"`
 	InlFuncsWithClosures  int    `help:"allow functions with closures to be inlined" concurrent:"ok"`
+	InlStaticInit         int    `help:"allow static initialization of inlined calls"`
 	InterfaceCycles       int    `help:"allow anonymous interface cycles"`
 	Libfuzzer             int    `help:"enable coverage instrumentation for libfuzzer"`
 	LocationLists         int    `help:"print information about DWARF location list creation"`

src/cmd/compile/internal/base/flag.go

@@ -167,6 +167,7 @@ func ParseFlags() {
 
 	Debug.ConcurrentOk = true
 	Debug.InlFuncsWithClosures = 1
+	Debug.InlStaticInit = 0
 	if buildcfg.Experiment.Unified {
 		Debug.Unified = 1
 	}

src/cmd/compile/internal/staticinit/sched.go

@@ -451,6 +451,10 @@ func (s *Schedule) addvalue(p *Plan, xoffset int64, n ir.Node) {
 }
 
 func (s *Schedule) staticAssignInlinedCall(l *ir.Name, loff int64, call *ir.InlinedCallExpr, typ *types.Type) bool {
+	if base.Debug.InlStaticInit == 0 {
+		return false
+	}
+
 	// Handle the special case of an inlined call of
 	// a function body with a single return statement,
 	// which turns into a single assignment plus a goto.

test/fixedbugs/issue56778.go

@@ -1,4 +1,4 @@
-// compiledir
+// compiledir -d=inlstaticinit=1
 
 // Copyright 2022 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

test/inline.go

@@ -1,4 +1,4 @@
-// errorcheckwithauto -0 -m -d=inlfuncswithclosures=1
+// errorcheckwithauto -0 -m -d=inlfuncswithclosures=1 -d=inlstaticinit=1
 
 // Copyright 2015 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

test/noinit.go

@@ -1,4 +1,4 @@
-// run
+// run -gcflags=-d=inlstaticinit=1
 //go:build !gcflags_noopt
 
 // Copyright 2010 The Go Authors. All rights reserved.