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cmd/compile: use zero constants in comparisons where possible

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Some integer comparisons with 1 and -1 can be rewritten as comparisons
with 0. For example, x < 1 is equivalent to x <= 0. This is an
advantageous transformation on riscv64 because comparisons with zero
do not require a constant to be loaded into a register. Other
architectures will likely benefit too and the transformation is
relatively benign on architectures that do not benefit.

Change-Id: I2ce9821dd7605a660eb71d76e83a61f9bae1bf25
Reviewed-on: https://go-review.googlesource.com/c/go/+/350831
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Munday <mike.munday@lowrisc.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Michael Munday 2021-09-20 21:39:39 +01:00
parent 0ff91e03db
commit 85d54a7667
4 changed files with 466 additions and 1 deletions
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9
src/cmd/compile/internal/ssa/_gen/generic.rules
View File

@ -518,8 +518,17 @@
(Leq32 (Const32 [0]) (Rsh32Ux64 _ (Const64 [c]))) && c > 0 => (ConstBool [true])
(Leq64 (Const64 [0]) (Rsh64Ux64 _ (Const64 [c]))) && c > 0 => (ConstBool [true])
// prefer equalities with zero
(Less(64|32|16|8) (Const(64|32|16|8) <t> [0]) x) && isNonNegative(x) => (Neq(64|32|16|8) (Const(64|32|16|8) <t> [0]) x)
(Less(64|32|16|8) x (Const(64|32|16|8) <t> [1])) && isNonNegative(x) => (Eq(64|32|16|8) (Const(64|32|16|8) <t> [0]) x)
(Less(64|32|16|8)U x (Const(64|32|16|8) <t> [1])) => (Eq(64|32|16|8) (Const(64|32|16|8) <t> [0]) x)
(Leq(64|32|16|8)U (Const(64|32|16|8) <t> [1]) x) => (Neq(64|32|16|8) (Const(64|32|16|8) <t> [0]) x)
// prefer comparisons with zero
(Less(64|32|16|8) x (Const(64|32|16|8) <t> [1])) => (Leq(64|32|16|8) x (Const(64|32|16|8) <t> [0]))
(Leq(64|32|16|8) x (Const(64|32|16|8) <t> [-1])) => (Less(64|32|16|8) x (Const(64|32|16|8) <t> [0]))
(Leq(64|32|16|8) (Const(64|32|16|8) <t> [1]) x) => (Less(64|32|16|8) (Const(64|32|16|8) <t> [0]) x)
(Less(64|32|16|8) (Const(64|32|16|8) <t> [-1]) x) => (Leq(64|32|16|8) (Const(64|32|16|8) <t> [0]) x)
// constant floating point comparisons
(Eq32F (Const32F [c]) (Const32F [d])) => (ConstBool [c == d])

420
src/cmd/compile/internal/ssa/rewritegeneric.go
View File

@ -11137,6 +11137,7 @@ func rewriteValuegeneric_OpIsSliceInBounds(v *Value) bool {
func rewriteValuegeneric_OpLeq16(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq16 (Const16 [c]) (Const16 [d]))
// result: (ConstBool [c <= d])
for {
@ -11196,11 +11197,46 @@ func rewriteValuegeneric_OpLeq16(v *Value) bool {
v.AuxInt = boolToAuxInt(true)
return true
}
// match: (Leq16 x (Const16 <t> [-1]))
// result: (Less16 x (Const16 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst16 {
break
}
t := v_1.Type
if auxIntToInt16(v_1.AuxInt) != -1 {
break
}
v.reset(OpLess16)
v0 := b.NewValue0(v.Pos, OpConst16, t)
v0.AuxInt = int16ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Leq16 (Const16 <t> [1]) x)
// result: (Less16 (Const16 <t> [0]) x)
for {
if v_0.Op != OpConst16 {
break
}
t := v_0.Type
if auxIntToInt16(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpLess16)
v0 := b.NewValue0(v.Pos, OpConst16, t)
v0.AuxInt = int16ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLeq16U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq16U (Const16 [c]) (Const16 [d]))
// result: (ConstBool [uint16(c) <= uint16(d)])
for {
@ -11216,6 +11252,23 @@ func rewriteValuegeneric_OpLeq16U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint16(c) <= uint16(d))
return true
}
// match: (Leq16U (Const16 <t> [1]) x)
// result: (Neq16 (Const16 <t> [0]) x)
for {
if v_0.Op != OpConst16 {
break
}
t := v_0.Type
if auxIntToInt16(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpNeq16)
v0 := b.NewValue0(v.Pos, OpConst16, t)
v0.AuxInt = int16ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Leq16U (Const16 [0]) _)
// result: (ConstBool [true])
for {
@ -11231,6 +11284,7 @@ func rewriteValuegeneric_OpLeq16U(v *Value) bool {
func rewriteValuegeneric_OpLeq32(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq32 (Const32 [c]) (Const32 [d]))
// result: (ConstBool [c <= d])
for {
@ -11290,6 +11344,40 @@ func rewriteValuegeneric_OpLeq32(v *Value) bool {
v.AuxInt = boolToAuxInt(true)
return true
}
// match: (Leq32 x (Const32 <t> [-1]))
// result: (Less32 x (Const32 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst32 {
break
}
t := v_1.Type
if auxIntToInt32(v_1.AuxInt) != -1 {
break
}
v.reset(OpLess32)
v0 := b.NewValue0(v.Pos, OpConst32, t)
v0.AuxInt = int32ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Leq32 (Const32 <t> [1]) x)
// result: (Less32 (Const32 <t> [0]) x)
for {
if v_0.Op != OpConst32 {
break
}
t := v_0.Type
if auxIntToInt32(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpLess32)
v0 := b.NewValue0(v.Pos, OpConst32, t)
v0.AuxInt = int32ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLeq32F(v *Value) bool {
@ -11315,6 +11403,7 @@ func rewriteValuegeneric_OpLeq32F(v *Value) bool {
func rewriteValuegeneric_OpLeq32U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq32U (Const32 [c]) (Const32 [d]))
// result: (ConstBool [uint32(c) <= uint32(d)])
for {
@ -11330,6 +11419,23 @@ func rewriteValuegeneric_OpLeq32U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint32(c) <= uint32(d))
return true
}
// match: (Leq32U (Const32 <t> [1]) x)
// result: (Neq32 (Const32 <t> [0]) x)
for {
if v_0.Op != OpConst32 {
break
}
t := v_0.Type
if auxIntToInt32(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpNeq32)
v0 := b.NewValue0(v.Pos, OpConst32, t)
v0.AuxInt = int32ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Leq32U (Const32 [0]) _)
// result: (ConstBool [true])
for {
@ -11345,6 +11451,7 @@ func rewriteValuegeneric_OpLeq32U(v *Value) bool {
func rewriteValuegeneric_OpLeq64(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq64 (Const64 [c]) (Const64 [d]))
// result: (ConstBool [c <= d])
for {
@ -11404,6 +11511,40 @@ func rewriteValuegeneric_OpLeq64(v *Value) bool {
v.AuxInt = boolToAuxInt(true)
return true
}
// match: (Leq64 x (Const64 <t> [-1]))
// result: (Less64 x (Const64 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst64 {
break
}
t := v_1.Type
if auxIntToInt64(v_1.AuxInt) != -1 {
break
}
v.reset(OpLess64)
v0 := b.NewValue0(v.Pos, OpConst64, t)
v0.AuxInt = int64ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Leq64 (Const64 <t> [1]) x)
// result: (Less64 (Const64 <t> [0]) x)
for {
if v_0.Op != OpConst64 {
break
}
t := v_0.Type
if auxIntToInt64(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpLess64)
v0 := b.NewValue0(v.Pos, OpConst64, t)
v0.AuxInt = int64ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLeq64F(v *Value) bool {
@ -11429,6 +11570,7 @@ func rewriteValuegeneric_OpLeq64F(v *Value) bool {
func rewriteValuegeneric_OpLeq64U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq64U (Const64 [c]) (Const64 [d]))
// result: (ConstBool [uint64(c) <= uint64(d)])
for {
@ -11444,6 +11586,23 @@ func rewriteValuegeneric_OpLeq64U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint64(c) <= uint64(d))
return true
}
// match: (Leq64U (Const64 <t> [1]) x)
// result: (Neq64 (Const64 <t> [0]) x)
for {
if v_0.Op != OpConst64 {
break
}
t := v_0.Type
if auxIntToInt64(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpNeq64)
v0 := b.NewValue0(v.Pos, OpConst64, t)
v0.AuxInt = int64ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Leq64U (Const64 [0]) _)
// result: (ConstBool [true])
for {
@ -11459,6 +11618,7 @@ func rewriteValuegeneric_OpLeq64U(v *Value) bool {
func rewriteValuegeneric_OpLeq8(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq8 (Const8 [c]) (Const8 [d]))
// result: (ConstBool [c <= d])
for {
@ -11518,11 +11678,46 @@ func rewriteValuegeneric_OpLeq8(v *Value) bool {
v.AuxInt = boolToAuxInt(true)
return true
}
// match: (Leq8 x (Const8 <t> [-1]))
// result: (Less8 x (Const8 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst8 {
break
}
t := v_1.Type
if auxIntToInt8(v_1.AuxInt) != -1 {
break
}
v.reset(OpLess8)
v0 := b.NewValue0(v.Pos, OpConst8, t)
v0.AuxInt = int8ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Leq8 (Const8 <t> [1]) x)
// result: (Less8 (Const8 <t> [0]) x)
for {
if v_0.Op != OpConst8 {
break
}
t := v_0.Type
if auxIntToInt8(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpLess8)
v0 := b.NewValue0(v.Pos, OpConst8, t)
v0.AuxInt = int8ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLeq8U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Leq8U (Const8 [c]) (Const8 [d]))
// result: (ConstBool [ uint8(c) <= uint8(d)])
for {
@ -11538,6 +11733,23 @@ func rewriteValuegeneric_OpLeq8U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint8(c) <= uint8(d))
return true
}
// match: (Leq8U (Const8 <t> [1]) x)
// result: (Neq8 (Const8 <t> [0]) x)
for {
if v_0.Op != OpConst8 {
break
}
t := v_0.Type
if auxIntToInt8(v_0.AuxInt) != 1 {
break
}
x := v_1
v.reset(OpNeq8)
v0 := b.NewValue0(v.Pos, OpConst8, t)
v0.AuxInt = int8ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Leq8U (Const8 [0]) _)
// result: (ConstBool [true])
for {
@ -11608,11 +11820,46 @@ func rewriteValuegeneric_OpLess16(v *Value) bool {
v.AddArg2(v0, x)
return true
}
// match: (Less16 x (Const16 <t> [1]))
// result: (Leq16 x (Const16 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst16 {
break
}
t := v_1.Type
if auxIntToInt16(v_1.AuxInt) != 1 {
break
}
v.reset(OpLeq16)
v0 := b.NewValue0(v.Pos, OpConst16, t)
v0.AuxInt = int16ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Less16 (Const16 <t> [-1]) x)
// result: (Leq16 (Const16 <t> [0]) x)
for {
if v_0.Op != OpConst16 {
break
}
t := v_0.Type
if auxIntToInt16(v_0.AuxInt) != -1 {
break
}
x := v_1
v.reset(OpLeq16)
v0 := b.NewValue0(v.Pos, OpConst16, t)
v0.AuxInt = int16ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLess16U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Less16U (Const16 [c]) (Const16 [d]))
// result: (ConstBool [uint16(c) < uint16(d)])
for {
@ -11628,6 +11875,23 @@ func rewriteValuegeneric_OpLess16U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint16(c) < uint16(d))
return true
}
// match: (Less16U x (Const16 <t> [1]))
// result: (Eq16 (Const16 <t> [0]) x)
for {
x := v_0
if v_1.Op != OpConst16 {
break
}
t := v_1.Type
if auxIntToInt16(v_1.AuxInt) != 1 {
break
}
v.reset(OpEq16)
v0 := b.NewValue0(v.Pos, OpConst16, t)
v0.AuxInt = int16ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Less16U _ (Const16 [0]))
// result: (ConstBool [false])
for {
@ -11698,6 +11962,40 @@ func rewriteValuegeneric_OpLess32(v *Value) bool {
v.AddArg2(v0, x)
return true
}
// match: (Less32 x (Const32 <t> [1]))
// result: (Leq32 x (Const32 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst32 {
break
}
t := v_1.Type
if auxIntToInt32(v_1.AuxInt) != 1 {
break
}
v.reset(OpLeq32)
v0 := b.NewValue0(v.Pos, OpConst32, t)
v0.AuxInt = int32ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Less32 (Const32 <t> [-1]) x)
// result: (Leq32 (Const32 <t> [0]) x)
for {
if v_0.Op != OpConst32 {
break
}
t := v_0.Type
if auxIntToInt32(v_0.AuxInt) != -1 {
break
}
x := v_1
v.reset(OpLeq32)
v0 := b.NewValue0(v.Pos, OpConst32, t)
v0.AuxInt = int32ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLess32F(v *Value) bool {
@ -11723,6 +12021,7 @@ func rewriteValuegeneric_OpLess32F(v *Value) bool {
func rewriteValuegeneric_OpLess32U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Less32U (Const32 [c]) (Const32 [d]))
// result: (ConstBool [uint32(c) < uint32(d)])
for {
@ -11738,6 +12037,23 @@ func rewriteValuegeneric_OpLess32U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint32(c) < uint32(d))
return true
}
// match: (Less32U x (Const32 <t> [1]))
// result: (Eq32 (Const32 <t> [0]) x)
for {
x := v_0
if v_1.Op != OpConst32 {
break
}
t := v_1.Type
if auxIntToInt32(v_1.AuxInt) != 1 {
break
}
v.reset(OpEq32)
v0 := b.NewValue0(v.Pos, OpConst32, t)
v0.AuxInt = int32ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Less32U _ (Const32 [0]))
// result: (ConstBool [false])
for {
@ -11808,6 +12124,40 @@ func rewriteValuegeneric_OpLess64(v *Value) bool {
v.AddArg2(v0, x)
return true
}
// match: (Less64 x (Const64 <t> [1]))
// result: (Leq64 x (Const64 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst64 {
break
}
t := v_1.Type
if auxIntToInt64(v_1.AuxInt) != 1 {
break
}
v.reset(OpLeq64)
v0 := b.NewValue0(v.Pos, OpConst64, t)
v0.AuxInt = int64ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Less64 (Const64 <t> [-1]) x)
// result: (Leq64 (Const64 <t> [0]) x)
for {
if v_0.Op != OpConst64 {
break
}
t := v_0.Type
if auxIntToInt64(v_0.AuxInt) != -1 {
break
}
x := v_1
v.reset(OpLeq64)
v0 := b.NewValue0(v.Pos, OpConst64, t)
v0.AuxInt = int64ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLess64F(v *Value) bool {
@ -11833,6 +12183,7 @@ func rewriteValuegeneric_OpLess64F(v *Value) bool {
func rewriteValuegeneric_OpLess64U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Less64U (Const64 [c]) (Const64 [d]))
// result: (ConstBool [uint64(c) < uint64(d)])
for {
@ -11848,6 +12199,23 @@ func rewriteValuegeneric_OpLess64U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint64(c) < uint64(d))
return true
}
// match: (Less64U x (Const64 <t> [1]))
// result: (Eq64 (Const64 <t> [0]) x)
for {
x := v_0
if v_1.Op != OpConst64 {
break
}
t := v_1.Type
if auxIntToInt64(v_1.AuxInt) != 1 {
break
}
v.reset(OpEq64)
v0 := b.NewValue0(v.Pos, OpConst64, t)
v0.AuxInt = int64ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Less64U _ (Const64 [0]))
// result: (ConstBool [false])
for {
@ -11918,11 +12286,46 @@ func rewriteValuegeneric_OpLess8(v *Value) bool {
v.AddArg2(v0, x)
return true
}
// match: (Less8 x (Const8 <t> [1]))
// result: (Leq8 x (Const8 <t> [0]))
for {
x := v_0
if v_1.Op != OpConst8 {
break
}
t := v_1.Type
if auxIntToInt8(v_1.AuxInt) != 1 {
break
}
v.reset(OpLeq8)
v0 := b.NewValue0(v.Pos, OpConst8, t)
v0.AuxInt = int8ToAuxInt(0)
v.AddArg2(x, v0)
return true
}
// match: (Less8 (Const8 <t> [-1]) x)
// result: (Leq8 (Const8 <t> [0]) x)
for {
if v_0.Op != OpConst8 {
break
}
t := v_0.Type
if auxIntToInt8(v_0.AuxInt) != -1 {
break
}
x := v_1
v.reset(OpLeq8)
v0 := b.NewValue0(v.Pos, OpConst8, t)
v0.AuxInt = int8ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
return false
}
func rewriteValuegeneric_OpLess8U(v *Value) bool {
v_1 := v.Args[1]
v_0 := v.Args[0]
b := v.Block
// match: (Less8U (Const8 [c]) (Const8 [d]))
// result: (ConstBool [ uint8(c) < uint8(d)])
for {
@ -11938,6 +12341,23 @@ func rewriteValuegeneric_OpLess8U(v *Value) bool {
v.AuxInt = boolToAuxInt(uint8(c) < uint8(d))
return true
}
// match: (Less8U x (Const8 <t> [1]))
// result: (Eq8 (Const8 <t> [0]) x)
for {
x := v_0
if v_1.Op != OpConst8 {
break
}
t := v_1.Type
if auxIntToInt8(v_1.AuxInt) != 1 {
break
}
v.reset(OpEq8)
v0 := b.NewValue0(v.Pos, OpConst8, t)
v0.AuxInt = int8ToAuxInt(0)
v.AddArg2(v0, x)
return true
}
// match: (Less8U _ (Const8 [0]))
// result: (ConstBool [false])
for {

36
test/codegen/compare_and_branch.go
View File

@ -204,3 +204,39 @@ func ui32xu8(x chan uint32) {
dummy()
}
}
// Signed 64-bit comparison with 1/-1 to comparison with 0.
func si64x0(x chan int64) {
// riscv64:"BGTZ"
for <-x >= 1 {
dummy()
}
// riscv64:"BLEZ"
for <-x < 1 {
dummy()
}
// riscv64:"BLTZ"
for <-x <= -1 {
dummy()
}
// riscv64:"BGEZ"
for <-x > -1 {
dummy()
}
}
// Unsigned 64-bit comparison with 1 to comparison with 0.
func ui64x0(x chan uint64) {
// riscv64:"BNEZ"
for <-x >= 1 {
dummy()
}
// riscv64:"BEQZ"
for <-x < 1 {
dummy()
}
}

2
test/prove.go
View File

@ -820,7 +820,7 @@ func unrollDownExcl0(a []int) int {
// Induction variable in unrolled loop.
func unrollDownExcl1(a []int) int {
var i, x int
for i = len(a) - 1; i >= 1; i -= 2 { // ERROR "Induction variable: limits \[1,\?\], increment 2$"
for i = len(a) - 1; i >= 1; i -= 2 { // ERROR "Induction variable: limits \(0,\?\], increment 2$"
x += a[i] // ERROR "Proved IsInBounds$"
x += a[i-1] // ERROR "Proved IsInBounds$"
}