cmd/compile: fold MOV*nop and MOV*const

MOV*nop and MOV*reg seem superfluous. They are there to keep type
information around that would otherwise get thrown away. Not sure
what we need it for. I think our compiler needs a normalization of
how types are represented in SSA, especially after lowering.

MOV*nop gets in the way of some optimization rules firing, like for
load combining.

For now, just fold MOV*nop and MOV*const. It's certainly safe to
do that, as the type info on the MOV*const isn't ever useful.

R=go1.17

Change-Id: I3630a80afc2455a8e9cd9fde10c7abe05ddc3767
Reviewed-on: https://go-review.googlesource.com/c/go/+/276792
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -546,6 +546,10 @@
 // MOVWnop doesn't emit instruction, only for ensuring the type.
 (MOVWreg x) && x.Uses == 1 => (MOVWnop x)
 
+// TODO: we should be able to get rid of MOVWnop all together.
+// But for now, this is enough to get rid of lots of them.
+(MOVWnop (MOVWconst [c])) => (MOVWconst [c])
+
 // mul by constant
 (MUL x (MOVWconst [c])) && int32(c) == -1 => (RSBconst [0] x)
 (MUL _ (MOVWconst [0])) => (MOVWconst [0])

src/cmd/compile/internal/ssa/gen/ARM64.rules

@@ -1127,6 +1127,10 @@
 // MOVDnop doesn't emit instruction, only for ensuring the type.
 (MOVDreg x) && x.Uses == 1 => (MOVDnop x)
 
+// TODO: we should be able to get rid of MOVDnop all together.
+// But for now, this is enough to get rid of lots of them.
+(MOVDnop (MOVDconst [c])) => (MOVDconst [c])
+
 // fold constant into arithmatic ops
 (ADD x (MOVDconst [c])) => (ADDconst [c] x)
 (SUB x (MOVDconst [c])) => (SUBconst [c] x)

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

@@ -559,6 +559,10 @@
 // MOVWnop doesn't emit instruction, only for ensuring the type.
 (MOVWreg x) && x.Uses == 1 => (MOVWnop x)
 
+// TODO: we should be able to get rid of MOVWnop all together.
+// But for now, this is enough to get rid of lots of them.
+(MOVWnop (MOVWconst [c])) => (MOVWconst [c])
+
 // fold constant into arithmatic ops
 (ADD x (MOVWconst [c])) => (ADDconst [c] x)
 (SUB x (MOVWconst [c])) => (SUBconst [c] x)

src/cmd/compile/internal/ssa/gen/MIPS64.rules

@@ -558,6 +558,10 @@
 // MOVVnop doesn't emit instruction, only for ensuring the type.
 (MOVVreg x) && x.Uses == 1 => (MOVVnop x)
 
+// TODO: we should be able to get rid of MOVVnop all together.
+// But for now, this is enough to get rid of lots of them.
+(MOVVnop (MOVVconst [c])) => (MOVVconst [c])
+
 // fold constant into arithmatic ops
 (ADDV x (MOVVconst [c])) && is32Bit(c) => (ADDVconst [c] x)
 (SUBV x (MOVVconst [c])) && is32Bit(c) => (SUBVconst [c] x)

src/cmd/compile/internal/ssa/gen/RISCV64.rules

@@ -673,6 +673,10 @@
 // MOVnop does not emit an instruction, only for ensuring the type.
 (MOVDreg x) && x.Uses == 1 => (MOVDnop x)
 
+// TODO: we should be able to get rid of MOVDnop all together.
+// But for now, this is enough to get rid of lots of them.
+(MOVDnop (MOVDconst [c])) => (MOVDconst [c])
+
 // Fold constant into immediate instructions where possible.
 (ADD (MOVBconst [val]) x) => (ADDI [int64(val)] x)
 (ADD (MOVHconst [val]) x) => (ADDI [int64(val)] x)

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

@@ -202,6 +202,8 @@ func rewriteValueARM(v *Value) bool {
 		return rewriteValueARM_OpARMMOVWloadshiftRA(v)
 	case OpARMMOVWloadshiftRL:
 		return rewriteValueARM_OpARMMOVWloadshiftRL(v)
+	case OpARMMOVWnop:
+		return rewriteValueARM_OpARMMOVWnop(v)
 	case OpARMMOVWreg:
 		return rewriteValueARM_OpARMMOVWreg(v)
 	case OpARMMOVWstore:
@@ -6501,6 +6503,21 @@ func rewriteValueARM_OpARMMOVWloadshiftRL(v *Value) bool {
 	}
 	return false
 }
+func rewriteValueARM_OpARMMOVWnop(v *Value) bool {
+	v_0 := v.Args[0]
+	// match: (MOVWnop (MOVWconst [c]))
+	// result: (MOVWconst [c])
+	for {
+		if v_0.Op != OpARMMOVWconst {
+			break
+		}
+		c := auxIntToInt32(v_0.AuxInt)
+		v.reset(OpARMMOVWconst)
+		v.AuxInt = int32ToAuxInt(c)
+		return true
+	}
+	return false
+}
 func rewriteValueARM_OpARMMOVWreg(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (MOVWreg x)

src/cmd/compile/internal/ssa/rewriteARM64.go

@@ -189,6 +189,8 @@ func rewriteValueARM64(v *Value) bool {
 		return rewriteValueARM64_OpARM64MOVDloadidx(v)
 	case OpARM64MOVDloadidx8:
 		return rewriteValueARM64_OpARM64MOVDloadidx8(v)
+	case OpARM64MOVDnop:
+		return rewriteValueARM64_OpARM64MOVDnop(v)
 	case OpARM64MOVDreg:
 		return rewriteValueARM64_OpARM64MOVDreg(v)
 	case OpARM64MOVDstore:
@@ -9011,6 +9013,21 @@ func rewriteValueARM64_OpARM64MOVDloadidx8(v *Value) bool {
 	}
 	return false
 }
+func rewriteValueARM64_OpARM64MOVDnop(v *Value) bool {
+	v_0 := v.Args[0]
+	// match: (MOVDnop (MOVDconst [c]))
+	// result: (MOVDconst [c])
+	for {
+		if v_0.Op != OpARM64MOVDconst {
+			break
+		}
+		c := auxIntToInt64(v_0.AuxInt)
+		v.reset(OpARM64MOVDconst)
+		v.AuxInt = int64ToAuxInt(c)
+		return true
+	}
+	return false
+}
 func rewriteValueARM64_OpARM64MOVDreg(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (MOVDreg x)

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

@@ -297,6 +297,8 @@ func rewriteValueMIPS(v *Value) bool {
 		return rewriteValueMIPS_OpMIPSMOVHstorezero(v)
 	case OpMIPSMOVWload:
 		return rewriteValueMIPS_OpMIPSMOVWload(v)
+	case OpMIPSMOVWnop:
+		return rewriteValueMIPS_OpMIPSMOVWnop(v)
 	case OpMIPSMOVWreg:
 		return rewriteValueMIPS_OpMIPSMOVWreg(v)
 	case OpMIPSMOVWstore:
@@ -3647,6 +3649,21 @@ func rewriteValueMIPS_OpMIPSMOVWload(v *Value) bool {
 	}
 	return false
 }
+func rewriteValueMIPS_OpMIPSMOVWnop(v *Value) bool {
+	v_0 := v.Args[0]
+	// match: (MOVWnop (MOVWconst [c]))
+	// result: (MOVWconst [c])
+	for {
+		if v_0.Op != OpMIPSMOVWconst {
+			break
+		}
+		c := auxIntToInt32(v_0.AuxInt)
+		v.reset(OpMIPSMOVWconst)
+		v.AuxInt = int32ToAuxInt(c)
+		return true
+	}
+	return false
+}
 func rewriteValueMIPS_OpMIPSMOVWreg(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (MOVWreg x)

src/cmd/compile/internal/ssa/rewriteMIPS64.go

@@ -339,6 +339,8 @@ func rewriteValueMIPS64(v *Value) bool {
 		return rewriteValueMIPS64_OpMIPS64MOVHstorezero(v)
 	case OpMIPS64MOVVload:
 		return rewriteValueMIPS64_OpMIPS64MOVVload(v)
+	case OpMIPS64MOVVnop:
+		return rewriteValueMIPS64_OpMIPS64MOVVnop(v)
 	case OpMIPS64MOVVreg:
 		return rewriteValueMIPS64_OpMIPS64MOVVreg(v)
 	case OpMIPS64MOVVstore:
@@ -3584,6 +3586,21 @@ func rewriteValueMIPS64_OpMIPS64MOVVload(v *Value) bool {
 	}
 	return false
 }
+func rewriteValueMIPS64_OpMIPS64MOVVnop(v *Value) bool {
+	v_0 := v.Args[0]
+	// match: (MOVVnop (MOVVconst [c]))
+	// result: (MOVVconst [c])
+	for {
+		if v_0.Op != OpMIPS64MOVVconst {
+			break
+		}
+		c := auxIntToInt64(v_0.AuxInt)
+		v.reset(OpMIPS64MOVVconst)
+		v.AuxInt = int64ToAuxInt(c)
+		return true
+	}
+	return false
+}
 func rewriteValueMIPS64_OpMIPS64MOVVreg(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (MOVVreg x)

src/cmd/compile/internal/ssa/rewriteRISCV64.go

@@ -435,6 +435,8 @@ func rewriteValueRISCV64(v *Value) bool {
 		return rewriteValueRISCV64_OpRISCV64MOVDconst(v)
 	case OpRISCV64MOVDload:
 		return rewriteValueRISCV64_OpRISCV64MOVDload(v)
+	case OpRISCV64MOVDnop:
+		return rewriteValueRISCV64_OpRISCV64MOVDnop(v)
 	case OpRISCV64MOVDreg:
 		return rewriteValueRISCV64_OpRISCV64MOVDreg(v)
 	case OpRISCV64MOVDstore:
@@ -3349,6 +3351,21 @@ func rewriteValueRISCV64_OpRISCV64MOVDload(v *Value) bool {
 	}
 	return false
 }
+func rewriteValueRISCV64_OpRISCV64MOVDnop(v *Value) bool {
+	v_0 := v.Args[0]
+	// match: (MOVDnop (MOVDconst [c]))
+	// result: (MOVDconst [c])
+	for {
+		if v_0.Op != OpRISCV64MOVDconst {
+			break
+		}
+		c := auxIntToInt64(v_0.AuxInt)
+		v.reset(OpRISCV64MOVDconst)
+		v.AuxInt = int64ToAuxInt(c)
+		return true
+	}
+	return false
+}
 func rewriteValueRISCV64_OpRISCV64MOVDreg(v *Value) bool {
 	v_0 := v.Args[0]
 	// match: (MOVDreg x)