cmd/compile: automate resultInArg0 register checks

No functional changes; passes toolstash-check.
No measureable performance changes.

Change-Id: I2629f73d4a3cc56d80f512f33cf57cf41d8f15d3
Reviewed-on: https://go-review.googlesource.com/c/go/+/296010
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

12 files changed, 52 insertions, 166 deletions

diff --git a/src/cmd/compile/internal/amd64/ssa.go b/src/cmd/compile/internal/amd64/ssa.go
index 6944ba7ce7..230219a383 100644
--- a/src/cmd/compile/internal/amd64/ssa.go
+++ b/src/cmd/compile/internal/amd64/ssa.go
@@ -202,9 +202,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.From = obj.Addr{Type: obj.TYPE_REG, Reg: v.Args[2].Reg()}
 		p.To = obj.Addr{Type: obj.TYPE_REG, Reg: v.Reg()}
 		p.SetFrom3(obj.Addr{Type: obj.TYPE_REG, Reg: v.Args[1].Reg()})
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 	case ssa.OpAMD64ADDQ, ssa.OpAMD64ADDL:
 		r := v.Reg()
 		r1 := v.Args[0].Reg()
@@ -254,11 +251,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssa.OpAMD64BTSL, ssa.OpAMD64BTSQ,
 		ssa.OpAMD64BTCL, ssa.OpAMD64BTCQ,
 		ssa.OpAMD64BTRL, ssa.OpAMD64BTRQ:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
-		opregreg(s, v.Op.Asm(), r, v.Args[1].Reg())
+		opregreg(s, v.Op.Asm(), v.Reg(), v.Args[1].Reg())
 
 	case ssa.OpAMD64DIVQU, ssa.OpAMD64DIVLU, ssa.OpAMD64DIVWU:
 		// Arg[0] (the dividend) is in AX.
@@ -401,20 +394,16 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		// compute (x+y)/2 unsigned.
 		// Do a 64-bit add, the overflow goes into the carry.
 		// Shift right once and pull the carry back into the 63rd bit.
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(x86.AADDQ)
 		p.From.Type = obj.TYPE_REG
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 		p.From.Reg = v.Args[1].Reg()
 		p = s.Prog(x86.ARCRQ)
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = 1
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 
 	case ssa.OpAMD64ADDQcarry, ssa.OpAMD64ADCQ:
 		r := v.Reg0()
@@ -530,21 +519,13 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssa.OpAMD64CMOVQCS, ssa.OpAMD64CMOVLCS, ssa.OpAMD64CMOVWCS,
 		ssa.OpAMD64CMOVQGTF, ssa.OpAMD64CMOVLGTF, ssa.OpAMD64CMOVWGTF,
 		ssa.OpAMD64CMOVQGEF, ssa.OpAMD64CMOVLGEF, ssa.OpAMD64CMOVWGEF:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = v.Args[1].Reg()
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 
 	case ssa.OpAMD64CMOVQNEF, ssa.OpAMD64CMOVLNEF, ssa.OpAMD64CMOVWNEF:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		// Flag condition: ^ZERO || PARITY
 		// Generate:
 		//   CMOV*NE  SRC,DST
@@ -553,7 +534,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = v.Args[1].Reg()
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 		var q *obj.Prog
 		if v.Op == ssa.OpAMD64CMOVQNEF {
 			q = s.Prog(x86.ACMOVQPS)
@@ -565,14 +546,9 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		q.From.Type = obj.TYPE_REG
 		q.From.Reg = v.Args[1].Reg()
 		q.To.Type = obj.TYPE_REG
-		q.To.Reg = r
+		q.To.Reg = v.Reg()
 
 	case ssa.OpAMD64CMOVQEQF, ssa.OpAMD64CMOVLEQF, ssa.OpAMD64CMOVWEQF:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
-
 		// Flag condition: ZERO && !PARITY
 		// Generate:
 		//   MOV      SRC,AX
@@ -589,7 +565,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
-		p.From.Reg = r
+		p.From.Reg = v.Reg()
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = x86.REG_AX
 		var q *obj.Prog
@@ -603,7 +579,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		q.From.Type = obj.TYPE_REG
 		q.From.Reg = x86.REG_AX
 		q.To.Type = obj.TYPE_REG
-		q.To.Reg = r
+		q.To.Reg = v.Reg()
 
 	case ssa.OpAMD64MULQconst, ssa.OpAMD64MULLconst:
 		r := v.Reg()
@@ -622,15 +598,11 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssa.OpAMD64SHRQconst, ssa.OpAMD64SHRLconst, ssa.OpAMD64SHRWconst, ssa.OpAMD64SHRBconst,
 		ssa.OpAMD64SARQconst, ssa.OpAMD64SARLconst, ssa.OpAMD64SARWconst, ssa.OpAMD64SARBconst,
 		ssa.OpAMD64ROLQconst, ssa.OpAMD64ROLLconst, ssa.OpAMD64ROLWconst, ssa.OpAMD64ROLBconst:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = v.AuxInt
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.OpAMD64SBBQcarrymask, ssa.OpAMD64SBBLcarrymask:
 		r := v.Reg()
 		p := s.Prog(v.Op.Asm())
@@ -913,9 +885,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssagen.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 	case ssa.OpAMD64ADDLloadidx1, ssa.OpAMD64ADDLloadidx4, ssa.OpAMD64ADDLloadidx8, ssa.OpAMD64ADDQloadidx1, ssa.OpAMD64ADDQloadidx8,
 		ssa.OpAMD64SUBLloadidx1, ssa.OpAMD64SUBLloadidx4, ssa.OpAMD64SUBLloadidx8, ssa.OpAMD64SUBQloadidx1, ssa.OpAMD64SUBQloadidx8,
 		ssa.OpAMD64ANDLloadidx1, ssa.OpAMD64ANDLloadidx4, ssa.OpAMD64ANDLloadidx8, ssa.OpAMD64ANDQloadidx1, ssa.OpAMD64ANDQloadidx8,
@@ -939,9 +908,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssagen.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 	case ssa.OpAMD64DUFFZERO:
 		if s.ABI != obj.ABIInternal {
 			v.Fatalf("MOVOconst can be only used in ABIInternal functions")
@@ -1078,22 +1044,14 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 	case ssa.OpAMD64NEGQ, ssa.OpAMD64NEGL,
 		ssa.OpAMD64BSWAPQ, ssa.OpAMD64BSWAPL,
 		ssa.OpAMD64NOTQ, ssa.OpAMD64NOTL:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 
 	case ssa.OpAMD64NEGLflags:
-		r := v.Reg0()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg0()
 
 	case ssa.OpAMD64BSFQ, ssa.OpAMD64BSRQ, ssa.OpAMD64BSFL, ssa.OpAMD64BSRL, ssa.OpAMD64SQRTSD:
 		p := s.Prog(v.Op.Asm())
@@ -1214,25 +1172,17 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg0()
 	case ssa.OpAMD64XCHGB, ssa.OpAMD64XCHGL, ssa.OpAMD64XCHGQ:
-		r := v.Reg0()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output[0] not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
-		p.From.Reg = r
+		p.From.Reg = v.Reg0()
 		p.To.Type = obj.TYPE_MEM
 		p.To.Reg = v.Args[1].Reg()
 		ssagen.AddAux(&p.To, v)
 	case ssa.OpAMD64XADDLlock, ssa.OpAMD64XADDQlock:
-		r := v.Reg0()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output[0] not in same register %s", v.LongString())
-		}
 		s.Prog(x86.ALOCK)
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
-		p.From.Reg = r
+		p.From.Reg = v.Reg0()
 		p.To.Type = obj.TYPE_MEM
 		p.To.Reg = v.Args[1].Reg()
 		ssagen.AddAux(&p.To, v)
diff --git a/src/cmd/compile/internal/arm/ssa.go b/src/cmd/compile/internal/arm/ssa.go
index 729d2dab2d..6cbdf4377d 100644
--- a/src/cmd/compile/internal/arm/ssa.go
+++ b/src/cmd/compile/internal/arm/ssa.go
@@ -173,9 +173,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = y
 	case ssa.OpARMMOVWnop:
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		// nothing to do
 	case ssa.OpLoadReg:
 		if v.Type.IsFlags() {
diff --git a/src/cmd/compile/internal/arm64/ssa.go b/src/cmd/compile/internal/arm64/ssa.go
index ca5eac72bf..2576aeb600 100644
--- a/src/cmd/compile/internal/arm64/ssa.go
+++ b/src/cmd/compile/internal/arm64/ssa.go
@@ -142,9 +142,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = y
 	case ssa.OpARM64MOVDnop:
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		// nothing to do
 	case ssa.OpLoadReg:
 		if v.Type.IsFlags() {
@@ -522,17 +519,13 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssagen.AddAux(&p.To, v)
 	case ssa.OpARM64BFI,
 		ssa.OpARM64BFXIL:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = v.AuxInt >> 8
 		p.SetFrom3(obj.Addr{Type: obj.TYPE_CONST, Offset: v.AuxInt & 0xff})
 		p.Reg = v.Args[1].Reg()
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.OpARM64SBFIZ,
 		ssa.OpARM64SBFX,
 		ssa.OpARM64UBFIZ,
diff --git a/src/cmd/compile/internal/mips/ssa.go b/src/cmd/compile/internal/mips/ssa.go
index f1cdbd3241..115e3cb8e2 100644
--- a/src/cmd/compile/internal/mips/ssa.go
+++ b/src/cmd/compile/internal/mips/ssa.go
@@ -112,9 +112,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 			p.To.Reg = y
 		}
 	case ssa.OpMIPSMOVWnop:
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		// nothing to do
 	case ssa.OpLoadReg:
 		if v.Type.IsFlags() {
@@ -244,9 +241,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
 	case ssa.OpMIPSCMOVZ:
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = v.Args[2].Reg()
@@ -254,9 +248,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
 	case ssa.OpMIPSCMOVZzero:
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = v.Args[1].Reg()
diff --git a/src/cmd/compile/internal/mips64/ssa.go b/src/cmd/compile/internal/mips64/ssa.go
index 14cf7af143..d9c47751e1 100644
--- a/src/cmd/compile/internal/mips64/ssa.go
+++ b/src/cmd/compile/internal/mips64/ssa.go
@@ -115,9 +115,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 			p.To.Reg = y
 		}
 	case ssa.OpMIPS64MOVVnop:
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		// nothing to do
 	case ssa.OpLoadReg:
 		if v.Type.IsFlags() {
diff --git a/src/cmd/compile/internal/riscv64/ssa.go b/src/cmd/compile/internal/riscv64/ssa.go
index 70c29a4b7b..0a3064323a 100644
--- a/src/cmd/compile/internal/riscv64/ssa.go
+++ b/src/cmd/compile/internal/riscv64/ssa.go
@@ -211,9 +211,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = rd
 	case ssa.OpRISCV64MOVDnop:
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		// nothing to do
 	case ssa.OpLoadReg:
 		if v.Type.IsFlags() {
diff --git a/src/cmd/compile/internal/s390x/ssa.go b/src/cmd/compile/internal/s390x/ssa.go
index d4c7a286e2..0c65f7a238 100644
--- a/src/cmd/compile/internal/s390x/ssa.go
+++ b/src/cmd/compile/internal/s390x/ssa.go
@@ -175,10 +175,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 			p.Reg = r1
 		}
 	case ssa.OpS390XRXSBG:
-		r1 := v.Reg()
-		if r1 != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		r2 := v.Args[1].Reg()
 		i := v.Aux.(s390x.RotateParams)
 		p := s.Prog(v.Op.Asm())
@@ -188,7 +184,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 			{Type: obj.TYPE_CONST, Offset: int64(i.Amount)},
 			{Type: obj.TYPE_REG, Reg: r2},
 		})
-		p.To = obj.Addr{Type: obj.TYPE_REG, Reg: r1}
+		p.To = obj.Addr{Type: obj.TYPE_REG, Reg: v.Reg()}
 	case ssa.OpS390XRISBGZ:
 		r1 := v.Reg()
 		r2 := v.Args[0].Reg()
@@ -233,12 +229,8 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 			p.Reg = r2
 		}
 	case ssa.OpS390XADDE, ssa.OpS390XSUBE:
-		r1 := v.Reg0()
-		if r1 != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		r2 := v.Args[1].Reg()
-		opregreg(s, v.Op.Asm(), r1, r2)
+		opregreg(s, v.Op.Asm(), v.Reg0(), r2)
 	case ssa.OpS390XADDCconst:
 		r1 := v.Reg0()
 		r3 := v.Args[0].Reg()
@@ -248,18 +240,10 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 	case ssa.OpS390XMULLD, ssa.OpS390XMULLW,
 		ssa.OpS390XMULHD, ssa.OpS390XMULHDU,
 		ssa.OpS390XFMULS, ssa.OpS390XFMUL, ssa.OpS390XFDIVS, ssa.OpS390XFDIV:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
-		opregreg(s, v.Op.Asm(), r, v.Args[1].Reg())
+		opregreg(s, v.Op.Asm(), v.Reg(), v.Args[1].Reg())
 	case ssa.OpS390XFSUBS, ssa.OpS390XFSUB,
 		ssa.OpS390XFADDS, ssa.OpS390XFADD:
-		r := v.Reg0()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
-		opregreg(s, v.Op.Asm(), r, v.Args[1].Reg())
+		opregreg(s, v.Op.Asm(), v.Reg0(), v.Args[1].Reg())
 	case ssa.OpS390XMLGR:
 		// MLGR Rx R3 -> R2:R3
 		r0 := v.Args[0].Reg()
@@ -274,10 +258,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.To.Type = obj.TYPE_REG
 	case ssa.OpS390XFMADD, ssa.OpS390XFMADDS,
 		ssa.OpS390XFMSUB, ssa.OpS390XFMSUBS:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		r1 := v.Args[1].Reg()
 		r2 := v.Args[2].Reg()
 		p := s.Prog(v.Op.Asm())
@@ -285,7 +265,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.From.Reg = r1
 		p.Reg = r2
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.OpS390XFIDBR:
 		switch v.AuxInt {
 		case 0, 1, 3, 4, 5, 6, 7:
@@ -361,15 +341,11 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssa.OpS390XANDconst, ssa.OpS390XANDWconst,
 		ssa.OpS390XORconst, ssa.OpS390XORWconst,
 		ssa.OpS390XXORconst, ssa.OpS390XXORWconst:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = v.AuxInt
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.OpS390XSLDconst, ssa.OpS390XSLWconst,
 		ssa.OpS390XSRDconst, ssa.OpS390XSRWconst,
 		ssa.OpS390XSRADconst, ssa.OpS390XSRAWconst,
@@ -441,16 +417,12 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssa.OpS390XANDWload, ssa.OpS390XANDload,
 		ssa.OpS390XORWload, ssa.OpS390XORload,
 		ssa.OpS390XXORWload, ssa.OpS390XXORload:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_MEM
 		p.From.Reg = v.Args[1].Reg()
 		ssagen.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.OpS390XMOVDload,
 		ssa.OpS390XMOVWZload, ssa.OpS390XMOVHZload, ssa.OpS390XMOVBZload,
 		ssa.OpS390XMOVDBRload, ssa.OpS390XMOVWBRload, ssa.OpS390XMOVHBRload,
@@ -608,16 +580,12 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 	case ssa.OpS390XSumBytes2, ssa.OpS390XSumBytes4, ssa.OpS390XSumBytes8:
 		v.Fatalf("SumBytes generated %s", v.LongString())
 	case ssa.OpS390XLOCGR:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = int64(v.Aux.(s390x.CCMask))
 		p.Reg = v.Args[1].Reg()
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.OpS390XFSQRT:
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
diff --git a/src/cmd/compile/internal/ssa/gen/main.go b/src/cmd/compile/internal/ssa/gen/main.go
index f5385389c3..8e5997b25a 100644
--- a/src/cmd/compile/internal/ssa/gen/main.go
+++ b/src/cmd/compile/internal/ssa/gen/main.go
@@ -407,6 +407,7 @@ func genOp() {
 	fmt.Fprintln(w, "func (o Op) IsCall() bool { return opcodeTable[o].call }")
 	fmt.Fprintln(w, "func (o Op) HasSideEffects() bool { return opcodeTable[o].hasSideEffects }")
 	fmt.Fprintln(w, "func (o Op) UnsafePoint() bool { return opcodeTable[o].unsafePoint }")
+	fmt.Fprintln(w, "func (o Op) ResultInArg0() bool { return opcodeTable[o].resultInArg0 }")
 
 	// generate registers
 	for _, a := range archs {
diff --git a/src/cmd/compile/internal/ssa/opGen.go b/src/cmd/compile/internal/ssa/opGen.go
index 551aa725b6..10ea57b36b 100644
--- a/src/cmd/compile/internal/ssa/opGen.go
+++ b/src/cmd/compile/internal/ssa/opGen.go
@@ -36193,6 +36193,7 @@ func (o Op) SymEffect() SymEffect { return opcodeTable[o].symEffect }
 func (o Op) IsCall() bool         { return opcodeTable[o].call }
 func (o Op) HasSideEffects() bool { return opcodeTable[o].hasSideEffects }
 func (o Op) UnsafePoint() bool    { return opcodeTable[o].unsafePoint }
+func (o Op) ResultInArg0() bool   { return opcodeTable[o].resultInArg0 }
 
 var registers386 = [...]Register{
 	{0, x86.REG_AX, 0, "AX"},
diff --git a/src/cmd/compile/internal/ssa/value.go b/src/cmd/compile/internal/ssa/value.go
index 6539631b9c..55e4b684c1 100644
--- a/src/cmd/compile/internal/ssa/value.go
+++ b/src/cmd/compile/internal/ssa/value.go
@@ -411,6 +411,23 @@ func (v *Value) isGenericIntConst() bool {
 	return v != nil && (v.Op == OpConst64 || v.Op == OpConst32 || v.Op == OpConst16 || v.Op == OpConst8)
 }
 
+// ResultReg returns the result register assigned to v, in cmd/internal/obj/$ARCH numbering.
+// It is similar to Reg and Reg0, except that it is usable interchangeably for all Value Ops.
+// If you know v.Op, using Reg or Reg0 (as appropriate) will be more efficient.
+func (v *Value) ResultReg() int16 {
+	reg := v.Block.Func.RegAlloc[v.ID]
+	if reg == nil {
+		v.Fatalf("nil reg for value: %s\n%s\n", v.LongString(), v.Block.Func)
+	}
+	if pair, ok := reg.(LocPair); ok {
+		reg = pair[0]
+	}
+	if reg == nil {
+		v.Fatalf("nil reg0 for value: %s\n%s\n", v.LongString(), v.Block.Func)
+	}
+	return reg.(*Register).objNum
+}
+
 // Reg returns the register assigned to v, in cmd/internal/obj/$ARCH numbering.
 func (v *Value) Reg() int16 {
 	reg := v.Block.Func.RegAlloc[v.ID]
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index d69eb17ca9..20acdbdc66 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -6509,6 +6509,10 @@ func genssa(f *ssa.Func, pp *objw.Progs) {
 			x := s.pp.Next
 			s.DebugFriendlySetPosFrom(v)
 
+			if v.Op.ResultInArg0() && v.ResultReg() != v.Args[0].Reg() {
+				v.Fatalf("input[0] and output not in same register %s", v.LongString())
+			}
+
 			switch v.Op {
 			case ssa.OpInitMem:
 				// memory arg needs no code
diff --git a/src/cmd/compile/internal/x86/ssa.go b/src/cmd/compile/internal/x86/ssa.go
index 00dfa07bf7..c5fe3ae2e2 100644
--- a/src/cmd/compile/internal/x86/ssa.go
+++ b/src/cmd/compile/internal/x86/ssa.go
@@ -161,31 +161,19 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssa.Op386PXOR,
 		ssa.Op386ADCL,
 		ssa.Op386SBBL:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
-		opregreg(s, v.Op.Asm(), r, v.Args[1].Reg())
+		opregreg(s, v.Op.Asm(), v.Reg(), v.Args[1].Reg())
 
 	case ssa.Op386ADDLcarry, ssa.Op386SUBLcarry:
 		// output 0 is carry/borrow, output 1 is the low 32 bits.
-		r := v.Reg0()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output[0] not in same register %s", v.LongString())
-		}
-		opregreg(s, v.Op.Asm(), r, v.Args[1].Reg())
+		opregreg(s, v.Op.Asm(), v.Reg0(), v.Args[1].Reg())
 
 	case ssa.Op386ADDLconstcarry, ssa.Op386SUBLconstcarry:
 		// output 0 is carry/borrow, output 1 is the low 32 bits.
-		r := v.Reg0()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output[0] not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = v.AuxInt
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg0()
 
 	case ssa.Op386DIVL, ssa.Op386DIVW,
 		ssa.Op386DIVLU, ssa.Op386DIVWU,
@@ -306,20 +294,16 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		// compute (x+y)/2 unsigned.
 		// Do a 32-bit add, the overflow goes into the carry.
 		// Shift right once and pull the carry back into the 31st bit.
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(x86.AADDL)
 		p.From.Type = obj.TYPE_REG
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 		p.From.Reg = v.Args[1].Reg()
 		p = s.Prog(x86.ARCRL)
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = 1
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 
 	case ssa.Op386ADDLconst:
 		r := v.Reg()
@@ -370,15 +354,11 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssa.Op386SHRLconst, ssa.Op386SHRWconst, ssa.Op386SHRBconst,
 		ssa.Op386SARLconst, ssa.Op386SARWconst, ssa.Op386SARBconst,
 		ssa.Op386ROLLconst, ssa.Op386ROLWconst, ssa.Op386ROLBconst:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = v.AuxInt
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.Op386SBBLcarrymask:
 		r := v.Reg()
 		p := s.Prog(v.Op.Asm())
@@ -536,9 +516,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssagen.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 	case ssa.Op386ADDLload, ssa.Op386SUBLload, ssa.Op386MULLload,
 		ssa.Op386ANDLload, ssa.Op386ORLload, ssa.Op386XORLload,
 		ssa.Op386ADDSDload, ssa.Op386ADDSSload, ssa.Op386SUBSDload, ssa.Op386SUBSSload,
@@ -549,9 +526,6 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		ssagen.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
-		if v.Reg() != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 	case ssa.Op386MOVSSstore, ssa.Op386MOVSDstore, ssa.Op386MOVLstore, ssa.Op386MOVWstore, ssa.Op386MOVBstore,
 		ssa.Op386ADDLmodify, ssa.Op386SUBLmodify, ssa.Op386ANDLmodify, ssa.Op386ORLmodify, ssa.Op386XORLmodify:
 		p := s.Prog(v.Op.Asm())
@@ -781,13 +755,9 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 	case ssa.Op386NEGL,
 		ssa.Op386BSWAPL,
 		ssa.Op386NOTL:
-		r := v.Reg()
-		if r != v.Args[0].Reg() {
-			v.Fatalf("input[0] and output not in same register %s", v.LongString())
-		}
 		p := s.Prog(v.Op.Asm())
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = r
+		p.To.Reg = v.Reg()
 	case ssa.Op386BSFL, ssa.Op386BSFW,
 		ssa.Op386BSRL, ssa.Op386BSRW,
 		ssa.Op386SQRTSD: