cmd/compile: prevent constant folding of +/- when result is NaN

Missed as part of CL 221790. It isn't just * and / that can make NaNs.

Update #36400
Fixes #38359

Change-Id: I3fa562f772fe03b510793a6dc0cf6189c0c3e652
Reviewed-on: https://go-review.googlesource.com/c/go/+/227860
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -103,8 +103,8 @@
 (Add16  (Const16 [c])  (Const16 [d]))  -> (Const16 [int64(int16(c+d))])
 (Add32  (Const32 [c])  (Const32 [d]))  -> (Const32 [int64(int32(c+d))])
 (Add64  (Const64 [c])  (Const64 [d]))  -> (Const64 [c+d])
-(Add32F (Const32F [c]) (Const32F [d])) -> (Const32F [auxFrom32F(auxTo32F(c) + auxTo32F(d))])
+(Add32F (Const32F [c]) (Const32F [d])) && !math.IsNaN(float64(auxTo32F(c) + auxTo32F(d))) -> (Const32F [auxFrom32F(auxTo32F(c) + auxTo32F(d))])
-(Add64F (Const64F [c]) (Const64F [d])) -> (Const64F [auxFrom64F(auxTo64F(c) + auxTo64F(d))])
+(Add64F (Const64F [c]) (Const64F [d])) && !math.IsNaN(auxTo64F(c) + auxTo64F(d)) -> (Const64F [auxFrom64F(auxTo64F(c) + auxTo64F(d))])
 (AddPtr <t> x (Const64 [c])) -> (OffPtr <t> x [c])
 (AddPtr <t> x (Const32 [c])) -> (OffPtr <t> x [c])
 
@@ -112,8 +112,8 @@
 (Sub16  (Const16 [c]) (Const16 [d]))   -> (Const16 [int64(int16(c-d))])
 (Sub32  (Const32 [c]) (Const32 [d]))   -> (Const32 [int64(int32(c-d))])
 (Sub64  (Const64 [c]) (Const64 [d]))   -> (Const64 [c-d])
-(Sub32F (Const32F [c]) (Const32F [d])) -> (Const32F [auxFrom32F(auxTo32F(c) - auxTo32F(d))])
+(Sub32F (Const32F [c]) (Const32F [d])) && !math.IsNaN(float64(auxTo32F(c) - auxTo32F(d))) -> (Const32F [auxFrom32F(auxTo32F(c) - auxTo32F(d))])
-(Sub64F (Const64F [c]) (Const64F [d])) -> (Const64F [auxFrom64F(auxTo64F(c) - auxTo64F(d))])
+(Sub64F (Const64F [c]) (Const64F [d])) && !math.IsNaN(auxTo64F(c) - auxTo64F(d)) -> (Const64F [auxFrom64F(auxTo64F(c) - auxTo64F(d))])
 
 (Mul8   (Const8 [c])   (Const8 [d]))   -> (Const8  [int64(int8(c*d))])
 (Mul16  (Const16 [c])  (Const16 [d]))  -> (Const16 [int64(int16(c*d))])

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

@@ -957,6 +957,7 @@ func rewriteValuegeneric_OpAdd32F(v *Value) bool {
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
 	// match: (Add32F (Const32F [c]) (Const32F [d]))
+	// cond: !math.IsNaN(float64(auxTo32F(c) + auxTo32F(d)))
 	// result: (Const32F [auxFrom32F(auxTo32F(c) + auxTo32F(d))])
 	for {
 		for _i0 := 0; _i0 <= 1; _i0, v_0, v_1 = _i0+1, v_1, v_0 {
@@ -968,6 +969,9 @@ func rewriteValuegeneric_OpAdd32F(v *Value) bool {
 				continue
 			}
 			d := v_1.AuxInt
+			if !(!math.IsNaN(float64(auxTo32F(c) + auxTo32F(d)))) {
+				continue
+			}
 			v.reset(OpConst32F)
 			v.AuxInt = auxFrom32F(auxTo32F(c) + auxTo32F(d))
 			return true
@@ -1233,6 +1237,7 @@ func rewriteValuegeneric_OpAdd64F(v *Value) bool {
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
 	// match: (Add64F (Const64F [c]) (Const64F [d]))
+	// cond: !math.IsNaN(auxTo64F(c) + auxTo64F(d))
 	// result: (Const64F [auxFrom64F(auxTo64F(c) + auxTo64F(d))])
 	for {
 		for _i0 := 0; _i0 <= 1; _i0, v_0, v_1 = _i0+1, v_1, v_0 {
@@ -1244,6 +1249,9 @@ func rewriteValuegeneric_OpAdd64F(v *Value) bool {
 				continue
 			}
 			d := v_1.AuxInt
+			if !(!math.IsNaN(auxTo64F(c) + auxTo64F(d))) {
+				continue
+			}
 			v.reset(OpConst64F)
 			v.AuxInt = auxFrom64F(auxTo64F(c) + auxTo64F(d))
 			return true
@@ -22641,6 +22649,7 @@ func rewriteValuegeneric_OpSub32F(v *Value) bool {
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
 	// match: (Sub32F (Const32F [c]) (Const32F [d]))
+	// cond: !math.IsNaN(float64(auxTo32F(c) - auxTo32F(d)))
 	// result: (Const32F [auxFrom32F(auxTo32F(c) - auxTo32F(d))])
 	for {
 		if v_0.Op != OpConst32F {
@@ -22651,6 +22660,9 @@ func rewriteValuegeneric_OpSub32F(v *Value) bool {
 			break
 		}
 		d := v_1.AuxInt
+		if !(!math.IsNaN(float64(auxTo32F(c) - auxTo32F(d)))) {
+			break
+		}
 		v.reset(OpConst32F)
 		v.AuxInt = auxFrom32F(auxTo32F(c) - auxTo32F(d))
 		return true
@@ -22879,6 +22891,7 @@ func rewriteValuegeneric_OpSub64F(v *Value) bool {
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
 	// match: (Sub64F (Const64F [c]) (Const64F [d]))
+	// cond: !math.IsNaN(auxTo64F(c) - auxTo64F(d))
 	// result: (Const64F [auxFrom64F(auxTo64F(c) - auxTo64F(d))])
 	for {
 		if v_0.Op != OpConst64F {
@@ -22889,6 +22902,9 @@ func rewriteValuegeneric_OpSub64F(v *Value) bool {
 			break
 		}
 		d := v_1.AuxInt
+		if !(!math.IsNaN(auxTo64F(c) - auxTo64F(d))) {
+			break
+		}
 		v.reset(OpConst64F)
 		v.AuxInt = auxFrom64F(auxTo64F(c) - auxTo64F(d))
 		return true

test/fixedbugs/issue38359.go

@@ -0,0 +1,19 @@
+// compile
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Make sure NaN-NaN compiles correctly.
+
+package p
+
+func f() {
+	var st struct {
+		f    float64
+		_, _ string
+	}
+
+	f := 1e308
+	st.f = 2*f - 2*f
+}