cmd/compile: avoid ifaceeq call if we know the interface is direct

We can just use == if the interface is direct.

Fixes #70738

Change-Id: Ia9a644791a370fec969c04c42d28a9b58f16911f
Reviewed-on: https://go-review.googlesource.com/c/go/+/635435
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/reflectdata/reflect.go

@@ -592,11 +592,21 @@ func TypePtrAt(pos src.XPos, t *types.Type) *ir.AddrExpr {
 // it may sometimes, but not always, be a type that can't implement the specified
 // interface.
 func ITabLsym(typ, iface *types.Type) *obj.LSym {
+	return itabLsym(typ, iface, true)
+}
+
+func itabLsym(typ, iface *types.Type, allowNonImplement bool) *obj.LSym {
 	s, existed := ir.Pkgs.Itab.LookupOK(typ.LinkString() + "," + iface.LinkString())
 	lsym := s.Linksym()
+	signatmu.Lock()
+	if lsym.Extra == nil {
+		ii := lsym.NewItabInfo()
+		ii.Type = typ
+	}
+	signatmu.Unlock()
 
 	if !existed {
-		writeITab(lsym, typ, iface, true)
+		writeITab(lsym, typ, iface, allowNonImplement)
 	}
 	return lsym
 }
@@ -605,13 +615,7 @@ func ITabLsym(typ, iface *types.Type) *obj.LSym {
 // *runtime.itab value for concrete type typ implementing interface
 // iface.
 func ITabAddrAt(pos src.XPos, typ, iface *types.Type) *ir.AddrExpr {
-	s, existed := ir.Pkgs.Itab.LookupOK(typ.LinkString() + "," + iface.LinkString())
-	lsym := s.Linksym()
-
-	if !existed {
-		writeITab(lsym, typ, iface, false)
-	}
-
+	lsym := itabLsym(typ, iface, false)
 	return typecheck.LinksymAddr(pos, lsym, types.Types[types.TUINT8])
 }
 

src/cmd/compile/internal/ssa/_gen/generic.rules

@@ -2072,6 +2072,11 @@
 (NilCheck          ptr:(Addr {_} (SB))    _) => ptr
 (NilCheck ptr:(Convert (Addr {_} (SB)) _) _) => ptr
 
+// Addresses of locals are always non-nil.
+(NilCheck ptr:(LocalAddr _ _) _)
+	&& warnRule(fe.Debug_checknil(), v, "removed nil check")
+	=> ptr
+
 // Nil checks of nil checks are redundant.
 // See comment at the end of https://go-review.googlesource.com/c/go/+/537775.
 (NilCheck ptr:(NilCheck _ _) _ ) => ptr
@@ -2774,3 +2779,19 @@
 // If we don't use the result of cmpstring, might as well not call it.
 // Note that this could pretty easily generalize to any pure function.
 (SelectN [1] c:(StaticLECall {f} _ _ mem)) && c.Uses == 1 && isSameCall(f, "runtime.cmpstring") && clobber(c) => mem
+
+// We can easily compute the result of efaceeq if
+// we know the underlying type is pointer-ish.
+(StaticLECall {f} typ_ x y mem)
+	&& isSameCall(f, "runtime.efaceeq")
+	&& isDirectType(typ_)
+	&& clobber(v)
+	=> (MakeResult (EqPtr x y) mem)
+
+// We can easily compute the result of ifaceeq if
+// we know the underlying type is pointer-ish.
+(StaticLECall {f} itab x y mem)
+	&& isSameCall(f, "runtime.ifaceeq")
+	&& isDirectIface(itab)
+	&& clobber(v)
+	=> (MakeResult (EqPtr x y) mem)

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

@@ -2424,3 +2424,86 @@ func rewriteStructStore(v *Value) *Value {
 
 	return mem
 }
+
+// isDirectType reports whether v represents a type
+// (a *runtime._type) whose value is stored directly in an
+// interface (i.e., is pointer or pointer-like).
+func isDirectType(v *Value) bool {
+	return isDirectType1(v)
+}
+
+// v is a type
+func isDirectType1(v *Value) bool {
+	switch v.Op {
+	case OpITab:
+		return isDirectType2(v.Args[0])
+	case OpAddr:
+		lsym := v.Aux.(*obj.LSym)
+		if lsym.Extra == nil {
+			return false
+		}
+		if ti, ok := (*lsym.Extra).(*obj.TypeInfo); ok {
+			return types.IsDirectIface(ti.Type.(*types.Type))
+		}
+	}
+	return false
+}
+
+// v is an empty interface
+func isDirectType2(v *Value) bool {
+	switch v.Op {
+	case OpIMake:
+		return isDirectType1(v.Args[0])
+	}
+	return false
+}
+
+// isDirectIface reports whether v represents an itab
+// (a *runtime._itab) for a type whose value is stored directly
+// in an interface (i.e., is pointer or pointer-like).
+func isDirectIface(v *Value) bool {
+	return isDirectIface1(v, 9)
+}
+
+// v is an itab
+func isDirectIface1(v *Value, depth int) bool {
+	if depth == 0 {
+		return false
+	}
+	switch v.Op {
+	case OpITab:
+		return isDirectIface2(v.Args[0], depth-1)
+	case OpAddr:
+		lsym := v.Aux.(*obj.LSym)
+		if lsym.Extra == nil {
+			return false
+		}
+		if ii, ok := (*lsym.Extra).(*obj.ItabInfo); ok {
+			return types.IsDirectIface(ii.Type.(*types.Type))
+		}
+	case OpConstNil:
+		// We can treat this as direct, because if the itab is
+		// nil, the data field must be nil also.
+		return true
+	}
+	return false
+}
+
+// v is an interface
+func isDirectIface2(v *Value, depth int) bool {
+	if depth == 0 {
+		return false
+	}
+	switch v.Op {
+	case OpIMake:
+		return isDirectIface1(v.Args[0], depth-1)
+	case OpPhi:
+		for _, a := range v.Args {
+			if !isDirectIface2(a, depth-1) {
+				return false
+			}
+		}
+		return true
+	}
+	return false
+}

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

@@ -20678,6 +20678,17 @@ func rewriteValuegeneric_OpNilCheck(v *Value) bool {
 		v.copyOf(ptr)
 		return true
 	}
+	// match: (NilCheck ptr:(LocalAddr _ _) _)
+	// cond: warnRule(fe.Debug_checknil(), v, "removed nil check")
+	// result: ptr
+	for {
+		ptr := v_0
+		if ptr.Op != OpLocalAddr || !(warnRule(fe.Debug_checknil(), v, "removed nil check")) {
+			break
+		}
+		v.copyOf(ptr)
+		return true
+	}
 	// match: (NilCheck ptr:(NilCheck _ _) _ )
 	// result: ptr
 	for {
@@ -30297,6 +30308,48 @@ func rewriteValuegeneric_OpStaticLECall(v *Value) bool {
 		v.AddArg2(v0, mem)
 		return true
 	}
+	// match: (StaticLECall {f} typ_ x y mem)
+	// cond: isSameCall(f, "runtime.efaceeq") && isDirectType(typ_) && clobber(v)
+	// result: (MakeResult (EqPtr x y) mem)
+	for {
+		if len(v.Args) != 4 {
+			break
+		}
+		f := auxToCall(v.Aux)
+		mem := v.Args[3]
+		typ_ := v.Args[0]
+		x := v.Args[1]
+		y := v.Args[2]
+		if !(isSameCall(f, "runtime.efaceeq") && isDirectType(typ_) && clobber(v)) {
+			break
+		}
+		v.reset(OpMakeResult)
+		v0 := b.NewValue0(v.Pos, OpEqPtr, typ.Bool)
+		v0.AddArg2(x, y)
+		v.AddArg2(v0, mem)
+		return true
+	}
+	// match: (StaticLECall {f} itab x y mem)
+	// cond: isSameCall(f, "runtime.ifaceeq") && isDirectIface(itab) && clobber(v)
+	// result: (MakeResult (EqPtr x y) mem)
+	for {
+		if len(v.Args) != 4 {
+			break
+		}
+		f := auxToCall(v.Aux)
+		mem := v.Args[3]
+		itab := v.Args[0]
+		x := v.Args[1]
+		y := v.Args[2]
+		if !(isSameCall(f, "runtime.ifaceeq") && isDirectIface(itab) && clobber(v)) {
+			break
+		}
+		v.reset(OpMakeResult)
+		v0 := b.NewValue0(v.Pos, OpEqPtr, typ.Bool)
+		v0.AddArg2(x, y)
+		v.AddArg2(v0, mem)
+		return true
+	}
 	return false
 }
 func rewriteValuegeneric_OpStore(v *Value) bool {

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

@@ -317,8 +317,17 @@ func walkCompare(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
 }
 
 func walkCompareInterface(n *ir.BinaryExpr, init *ir.Nodes) ir.Node {
+	swap := n.X.Op() != ir.OCONVIFACE && n.Y.Op() == ir.OCONVIFACE
 	n.Y = cheapExpr(n.Y, init)
 	n.X = cheapExpr(n.X, init)
+	if swap {
+		// Put the concrete type first in the comparison.
+		// This passes a constant type (itab) to efaceeq (ifaceeq)
+		// which is easier to match against in rewrite rules.
+		// See issue 70738.
+		n.X, n.Y = n.Y, n.X
+	}
+
 	eqtab, eqdata := compare.EqInterface(n.X, n.Y)
 	var cmp ir.Node
 	if n.Op() == ir.OEQ {

src/cmd/internal/obj/link.go

@@ -603,6 +603,22 @@ func (s *LSym) NewTypeInfo() *TypeInfo {
 	return t
 }
 
+// An ItabInfo contains information for a symbol
+// that contains a runtime.itab.
+type ItabInfo struct {
+	Type interface{} // a *cmd/compile/internal/types.Type
+}
+
+func (s *LSym) NewItabInfo() *ItabInfo {
+	if s.Extra != nil {
+		panic(fmt.Sprintf("invalid use of LSym - NewItabInfo with Extra of type %T", *s.Extra))
+	}
+	t := new(ItabInfo)
+	s.Extra = new(interface{})
+	*s.Extra = t
+	return t
+}
+
 // WasmImport represents a WebAssembly (WASM) imported function with
 // parameters and results translated into WASM types based on the Go function
 // declaration.

test/codegen/ifaces.go

@@ -25,3 +25,39 @@ func ConvToM(x any) I {
 	// arm64:`CALL\truntime.typeAssert`,`LDAR`,`MOVWU`,`MOVD\t\(R.*\)\(R.*\)`
 	return x.(I)
 }
+
+func e1(x any, y *int) bool {
+	// amd64:-`.*faceeq`,`SETEQ`
+	// arm64:-`.*faceeq`,`CSET\tEQ`
+	return x == y
+}
+
+func e2(x any, y *int) bool {
+	// amd64:-`.*faceeq`,`SETEQ`
+	// arm64:-`.*faceeq`,`CSET\tEQ`
+	return y == x
+}
+
+type E *int
+
+func e3(x any, y E) bool {
+	// amd64:-`.*faceeq`,`SETEQ`
+	// arm64:-`.*faceeq`,`CSET\tEQ`
+	return x == y
+}
+
+type T int
+
+func (t *T) M() {}
+
+func i1(x I, y *T) bool {
+	// amd64:-`.*faceeq`,`SETEQ`
+	// arm64:-`.*faceeq`,`CSET\tEQ`
+	return x == y
+}
+
+func i2(x I, y *T) bool {
+	// amd64:-`.*faceeq`,`SETEQ`
+	// arm64:-`.*faceeq`,`CSET\tEQ`
+	return y == x
+}