cmd/compile: add Func.SetNilCheckDisabled

Generated hash and eq routines don't need nil checks.
Prior to this CL, this was accomplished by
temporarily incrementing the global variable disable_checknil.
However, that increment lasted only the lifetime of the
call to funccompile. After CL 41503, funccompile may
do nothing but enqueue the function for compilation,
resulting in nil checks being generated.

Fix this by adding an explicit flag to a function
indicating whether nil checks should be disabled
for that function.

While we're here, allow concurrent compilation
with the -w and -W flags, since that was needed
to investigate this issue.

Fixes #20242

Change-Id: Ib9140c22c49e9a09e62fa3cf350f5d3eff18e2bd
Reviewed-on: https://go-review.googlesource.com/42591
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marvin Stenger <marvin.stenger94@gmail.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/gc/alg.go

@@ -311,9 +311,8 @@ func genhash(sym *types.Sym, t *types.Type) {
 	old_safemode := safemode
 	safemode = false
 
-	disable_checknil++
+	fn.Func.SetNilCheckDisabled(true)
 	funccompile(fn)
-	disable_checknil--
 
 	safemode = old_safemode
 }
@@ -500,12 +499,10 @@ func geneq(sym *types.Sym, t *types.Type) {
 	// We are comparing a struct or an array,
 	// neither of which can be nil, and our comparisons
 	// are shallow.
-	disable_checknil++
-
+	fn.Func.SetNilCheckDisabled(true)
 	funccompile(fn)
 
 	safemode = old_safemode
-	disable_checknil--
 }
 
 // eqfield returns the node

src/cmd/compile/internal/gc/main.go

@@ -1087,6 +1087,8 @@ var concurrentFlagOK = [256]bool{
 	'I': true, // add `directory` to import search path
 	'N': true, // disable optimizations
 	'l': true, // disable inlining
+	'w': true, // all printing happens before compilation
+	'W': true, // all printing happens before compilation
 }
 
 func concurrentBackendAllowed() bool {

src/cmd/compile/internal/gc/ssa.go

@@ -3399,7 +3399,7 @@ func (s *state) exprPtr(n *Node, bounded bool, lineno src.XPos) *ssa.Value {
 // Used only for automatically inserted nil checks,
 // not for user code like 'x != nil'.
 func (s *state) nilCheck(ptr *ssa.Value) {
-	if disable_checknil != 0 {
+	if disable_checknil != 0 || s.curfn.Func.NilCheckDisabled() {
 		return
 	}
 	s.newValue2(ssa.OpNilCheck, ssa.TypeVoid, ptr, s.mem())

src/cmd/compile/internal/gc/syntax.go

@@ -386,25 +386,28 @@ const (
 	funcNeedctxt                  // function uses context register (has closure variables)
 	funcReflectMethod             // function calls reflect.Type.Method or MethodByName
 	funcIsHiddenClosure
-	funcNoFramePointer // Must not use a frame pointer for this function
-	funcHasDefer       // contains a defer statement
+	funcNoFramePointer   // Must not use a frame pointer for this function
+	funcHasDefer         // contains a defer statement
+	funcNilCheckDisabled // disable nil checks when compiling this function
 )
 
-func (f *Func) Dupok() bool           { return f.flags&funcDupok != 0 }
-func (f *Func) Wrapper() bool         { return f.flags&funcWrapper != 0 }
-func (f *Func) Needctxt() bool        { return f.flags&funcNeedctxt != 0 }
-func (f *Func) ReflectMethod() bool   { return f.flags&funcReflectMethod != 0 }
-func (f *Func) IsHiddenClosure() bool { return f.flags&funcIsHiddenClosure != 0 }
-func (f *Func) NoFramePointer() bool  { return f.flags&funcNoFramePointer != 0 }
-func (f *Func) HasDefer() bool        { return f.flags&funcHasDefer != 0 }
-
-func (f *Func) SetDupok(b bool)           { f.flags.set(funcDupok, b) }
-func (f *Func) SetWrapper(b bool)         { f.flags.set(funcWrapper, b) }
-func (f *Func) SetNeedctxt(b bool)        { f.flags.set(funcNeedctxt, b) }
-func (f *Func) SetReflectMethod(b bool)   { f.flags.set(funcReflectMethod, b) }
-func (f *Func) SetIsHiddenClosure(b bool) { f.flags.set(funcIsHiddenClosure, b) }
-func (f *Func) SetNoFramePointer(b bool)  { f.flags.set(funcNoFramePointer, b) }
-func (f *Func) SetHasDefer(b bool)        { f.flags.set(funcHasDefer, b) }
+func (f *Func) Dupok() bool            { return f.flags&funcDupok != 0 }
+func (f *Func) Wrapper() bool          { return f.flags&funcWrapper != 0 }
+func (f *Func) Needctxt() bool         { return f.flags&funcNeedctxt != 0 }
+func (f *Func) ReflectMethod() bool    { return f.flags&funcReflectMethod != 0 }
+func (f *Func) IsHiddenClosure() bool  { return f.flags&funcIsHiddenClosure != 0 }
+func (f *Func) NoFramePointer() bool   { return f.flags&funcNoFramePointer != 0 }
+func (f *Func) HasDefer() bool         { return f.flags&funcHasDefer != 0 }
+func (f *Func) NilCheckDisabled() bool { return f.flags&funcNilCheckDisabled != 0 }
+
+func (f *Func) SetDupok(b bool)            { f.flags.set(funcDupok, b) }
+func (f *Func) SetWrapper(b bool)          { f.flags.set(funcWrapper, b) }
+func (f *Func) SetNeedctxt(b bool)         { f.flags.set(funcNeedctxt, b) }
+func (f *Func) SetReflectMethod(b bool)    { f.flags.set(funcReflectMethod, b) }
+func (f *Func) SetIsHiddenClosure(b bool)  { f.flags.set(funcIsHiddenClosure, b) }
+func (f *Func) SetNoFramePointer(b bool)   { f.flags.set(funcNoFramePointer, b) }
+func (f *Func) SetHasDefer(b bool)         { f.flags.set(funcHasDefer, b) }
+func (f *Func) SetNilCheckDisabled(b bool) { f.flags.set(funcNilCheckDisabled, b) }
 
 type Op uint8