cmd/compile: don't depend on arch-dependent conversions in the compiler

Leave those constant foldings for runtime, similar to how we do it
for NaN generation.

These are the only instances I could find in cmd/compile/..., using

objdump -d ../pkg/tool/darwin_arm64/compile| egrep "(fcvtz|>:)" | grep -B1 fcvt

(There are instances in other places, like runtime and reflect, but I don't
think those places would affect compiler output.)

Change-Id: I4113fe4570115e4765825cf442cb1fde97cf2f27
Reviewed-on: https://go-review.googlesource.com/c/go/+/711281
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>

2 files changed, 20 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/ssa/_gen/generic.rules b/src/cmd/compile/internal/ssa/_gen/generic.rules
index 23ce21a8b2..af9c24f53f 100644
--- a/src/cmd/compile/internal/ssa/_gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/_gen/generic.rules
@@ -50,10 +50,10 @@
 (Cvt32to64F  (Const32  [c])) => (Const64F [float64(c)])
 (Cvt64to32F  (Const64  [c])) => (Const32F [float32(c)])
 (Cvt64to64F  (Const64  [c])) => (Const64F [float64(c)])
-(Cvt32Fto32  (Const32F [c])) => (Const32  [int32(c)])
-(Cvt32Fto64  (Const32F [c])) => (Const64  [int64(c)])
-(Cvt64Fto32  (Const64F [c])) => (Const32  [int32(c)])
-(Cvt64Fto64  (Const64F [c])) => (Const64  [int64(c)])
+(Cvt32Fto32  (Const32F [c])) && c >= -1<<31 && c < 1<<31 => (Const32 [int32(c)])
+(Cvt32Fto64  (Const32F [c])) && c >= -1<<63 && c < 1<<63 => (Const64 [int64(c)])
+(Cvt64Fto32  (Const64F [c])) && c >= -1<<31 && c < 1<<31 => (Const32 [int32(c)])
+(Cvt64Fto64  (Const64F [c])) && c >= -1<<63 && c < 1<<63 => (Const64 [int64(c)])
 (Round32F x:(Const32F)) => x
 (Round64F x:(Const64F)) => x
 (CvtBoolToUint8 (ConstBool [false])) => (Const8 [0])
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index c36ecc1cc6..79c444a86b 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -6607,12 +6607,16 @@ func rewriteValuegeneric_OpCtz8(v *Value) bool {
 func rewriteValuegeneric_OpCvt32Fto32(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (Cvt32Fto32 (Const32F [c]))
+	// cond: c >= -1<<31 && c < 1<<31
 	// result: (Const32 [int32(c)])
 	for {
 		if v_0.Op != OpConst32F {
 			break
 		}
 		c := auxIntToFloat32(v_0.AuxInt)
+		if !(c >= -1<<31 && c < 1<<31) {
+			break
+		}
 		v.reset(OpConst32)
 		v.AuxInt = int32ToAuxInt(int32(c))
 		return true
@@ -6622,12 +6626,16 @@ func rewriteValuegeneric_OpCvt32Fto32(v *Value) bool {
 func rewriteValuegeneric_OpCvt32Fto64(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (Cvt32Fto64 (Const32F [c]))
+	// cond: c >= -1<<63 && c < 1<<63
 	// result: (Const64 [int64(c)])
 	for {
 		if v_0.Op != OpConst32F {
 			break
 		}
 		c := auxIntToFloat32(v_0.AuxInt)
+		if !(c >= -1<<63 && c < 1<<63) {
+			break
+		}
 		v.reset(OpConst64)
 		v.AuxInt = int64ToAuxInt(int64(c))
 		return true
@@ -6682,12 +6690,16 @@ func rewriteValuegeneric_OpCvt32to64F(v *Value) bool {
 func rewriteValuegeneric_OpCvt64Fto32(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (Cvt64Fto32 (Const64F [c]))
+	// cond: c >= -1<<31 && c < 1<<31
 	// result: (Const32 [int32(c)])
 	for {
 		if v_0.Op != OpConst64F {
 			break
 		}
 		c := auxIntToFloat64(v_0.AuxInt)
+		if !(c >= -1<<31 && c < 1<<31) {
+			break
+		}
 		v.reset(OpConst32)
 		v.AuxInt = int32ToAuxInt(int32(c))
 		return true
@@ -6732,12 +6744,16 @@ func rewriteValuegeneric_OpCvt64Fto32F(v *Value) bool {
 func rewriteValuegeneric_OpCvt64Fto64(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (Cvt64Fto64 (Const64F [c]))
+	// cond: c >= -1<<63 && c < 1<<63
 	// result: (Const64 [int64(c)])
 	for {
 		if v_0.Op != OpConst64F {
 			break
 		}
 		c := auxIntToFloat64(v_0.AuxInt)
+		if !(c >= -1<<63 && c < 1<<63) {
+			break
+		}
 		v.reset(OpConst64)
 		v.AuxInt = int64ToAuxInt(int64(c))
 		return true