cmd/compile: set/unset base register for better assembly print

For address of an auto or arg, on all non-x86 architectures
the assembler backend encodes the actual SP offset in the
instruction but leaves the offset in Prog unchanged. When the
assembly is printed in compile -S, it shows an offset
relative to pseudo FP/SP with an actual hardware SP base
register (e.g. R13 on ARM). This is confusing. Unset the
base register if it is indeed SP, so the assembly output is
consistent. If the base register isn't SP, it should be an
error and the error output contains the actual base register.

For address loading instructions, the base register isn't set
in the compiler on non-x86 architectures. Set it. Normally it
is SP and will be unset in the change mentioned above for
printing. If it is not, it will be an error and the error
output contains the actual base register.

No change in generated binary, only printed assembly. Passes
"go build -a -toolexec 'toolstash -cmp' std cmd" on all
architectures.

Fixes #21064.

Change-Id: Ifafe8d5f9b437efbe824b63b3cbc2f5f6cdc1fd5
Reviewed-on: https://go-review.googlesource.com/49432
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -464,6 +464,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 	case ssa.OpARMMOVWaddr:
 		p := s.Prog(arm.AMOVW)
 		p.From.Type = obj.TYPE_ADDR
+		p.From.Reg = v.Args[0].Reg()
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
 
@@ -485,7 +486,6 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		case nil:
 			// No sym, just MOVW $off(SP), R
 			wantreg = "SP"
-			p.From.Reg = arm.REGSP
 			p.From.Offset = v.AuxInt
 		}
 		if reg := v.Args[0].RegName(); reg != wantreg {

src/cmd/compile/internal/arm64/ssa.go

@@ -260,6 +260,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 	case ssa.OpARM64MOVDaddr:
 		p := s.Prog(arm64.AMOVD)
 		p.From.Type = obj.TYPE_ADDR
+		p.From.Reg = v.Args[0].Reg()
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
 
@@ -281,7 +282,6 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		case nil:
 			// No sym, just MOVD $off(SP), R
 			wantreg = "SP"
-			p.From.Reg = arm64.REGSP
 			p.From.Offset = v.AuxInt
 		}
 		if reg := v.Args[0].RegName(); reg != wantreg {

src/cmd/compile/internal/gc/asm_test.go

@@ -898,6 +898,17 @@ var linuxAMD64Tests = []*asmTest{
 		}`,
 		[]string{"\tCMPL\t[A-Z]"},
 	},
+	{
+		// make sure assembly output has matching offset and base register.
+		`
+		func f72(a, b int) int {
+			var x [16]byte // use some frame
+			_ = x
+			return b
+		}
+		`,
+		[]string{"b\\+40\\(SP\\)"},
+	},
 }
 
 var linux386Tests = []*asmTest{
@@ -1302,6 +1313,17 @@ var linuxARMTests = []*asmTest{
 		`,
 		[]string{"\tCLZ\t"},
 	},
+	{
+		// make sure assembly output has matching offset and base register.
+		`
+		func f13(a, b int) int {
+			var x [16]byte // use some frame
+			_ = x
+			return b
+		}
+		`,
+		[]string{"b\\+4\\(FP\\)"},
+	},
 }
 
 var linuxARM64Tests = []*asmTest{
@@ -1473,7 +1495,7 @@ var linuxARM64Tests = []*asmTest{
 			return
 		}
 		`,
-		[]string{"\tMOVD\t\"\"\\.a\\+[0-9]+\\(RSP\\), R[0-9]+", "\tMOVD\tR[0-9]+, \"\"\\.b\\+[0-9]+\\(RSP\\)"},
+		[]string{"\tMOVD\t\"\"\\.a\\+[0-9]+\\(FP\\), R[0-9]+", "\tMOVD\tR[0-9]+, \"\"\\.b\\+[0-9]+\\(FP\\)"},
 	},
 }
 

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

@@ -273,6 +273,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 	case ssa.OpMIPSMOVWaddr:
 		p := s.Prog(mips.AMOVW)
 		p.From.Type = obj.TYPE_ADDR
+		p.From.Reg = v.Args[0].Reg()
 		var wantreg string
 		// MOVW $sym+off(base), R
 		// the assembler expands it as the following:
@@ -291,7 +292,6 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		case nil:
 			// No sym, just MOVW $off(SP), R
 			wantreg = "SP"
-			p.From.Reg = mips.REGSP
 			p.From.Offset = v.AuxInt
 		}
 		if reg := v.Args[0].RegName(); reg != wantreg {

src/cmd/compile/internal/mips64/ssa.go

@@ -247,6 +247,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 	case ssa.OpMIPS64MOVVaddr:
 		p := s.Prog(mips.AMOVV)
 		p.From.Type = obj.TYPE_ADDR
+		p.From.Reg = v.Args[0].Reg()
 		var wantreg string
 		// MOVV $sym+off(base), R
 		// the assembler expands it as the following:
@@ -265,7 +266,6 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		case nil:
 			// No sym, just MOVV $off(SP), R
 			wantreg = "SP"
-			p.From.Reg = mips.REGSP
 			p.From.Offset = v.AuxInt
 		}
 		if reg := v.Args[0].RegName(); reg != wantreg {

src/cmd/compile/internal/ppc64/ssa.go

@@ -638,6 +638,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 	case ssa.OpPPC64MOVDaddr:
 		p := s.Prog(ppc64.AMOVD)
 		p.From.Type = obj.TYPE_ADDR
+		p.From.Reg = v.Args[0].Reg()
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = v.Reg()
 
@@ -660,7 +661,6 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		case nil:
 			// No sym, just MOVD $off(SP), R
 			wantreg = "SP"
-			p.From.Reg = ppc64.REGSP
 			p.From.Offset = v.AuxInt
 		}
 		if reg := v.Args[0].RegName(); reg != wantreg {

src/cmd/internal/obj/arm/asm5.go

@@ -1167,6 +1167,11 @@ func (c *ctxt5) aclass(a *obj.Addr) int {
 			return C_ADDR
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = c.autosize + a.Offset
 			if t := immaddr(int32(c.instoffset)); t != 0 {
 				if immhalf(int32(c.instoffset)) {
@@ -1185,6 +1190,11 @@ func (c *ctxt5) aclass(a *obj.Addr) int {
 			return C_LAUTO
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = c.autosize + a.Offset + 4
 			if t := immaddr(int32(c.instoffset)); t != 0 {
 				if immhalf(int32(c.instoffset)) {
@@ -1285,10 +1295,20 @@ func (c *ctxt5) aclass(a *obj.Addr) int {
 			return C_LCONADDR
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = c.autosize + a.Offset
 			return c.aconsize()
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = c.autosize + a.Offset + 4
 			return c.aconsize()
 		}

src/cmd/internal/obj/arm64/asm7.go

@@ -1149,10 +1149,20 @@ func (c *ctxt7) aclass(a *obj.Addr) int {
 			return C_GOTADDR
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			return autoclass(c.instoffset)
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + 8
 			return autoclass(c.instoffset)
 
@@ -1228,10 +1238,20 @@ func (c *ctxt7) aclass(a *obj.Addr) int {
 			return C_VCONADDR
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			goto aconsize
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + 8
 			goto aconsize
 		}

src/cmd/internal/obj/mips/asm0.go

@@ -556,6 +556,11 @@ func (c *ctxt0) aclass(a *obj.Addr) int {
 			return C_LEXT
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SAUTO
@@ -563,6 +568,11 @@ func (c *ctxt0) aclass(a *obj.Addr) int {
 			return C_LAUTO
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + c.ctxt.FixedFrameSize()
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SAUTO
@@ -616,6 +626,11 @@ func (c *ctxt0) aclass(a *obj.Addr) int {
 			return C_LECON
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SACON
@@ -623,6 +638,11 @@ func (c *ctxt0) aclass(a *obj.Addr) int {
 			return C_LACON
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + c.ctxt.FixedFrameSize()
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SACON

src/cmd/internal/obj/ppc64/asm9.go

@@ -758,6 +758,11 @@ func (c *ctxt9) aclass(a *obj.Addr) int {
 			return C_GOTADDR
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SAUTO
@@ -765,6 +770,11 @@ func (c *ctxt9) aclass(a *obj.Addr) int {
 			return C_LAUTO
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + c.ctxt.FixedFrameSize()
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SAUTO
@@ -817,6 +827,11 @@ func (c *ctxt9) aclass(a *obj.Addr) int {
 			return C_LCON
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SACON
@@ -824,6 +839,11 @@ func (c *ctxt9) aclass(a *obj.Addr) int {
 			return C_LACON
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + c.ctxt.FixedFrameSize()
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SACON

src/cmd/internal/obj/s390x/asmz.go

@@ -505,6 +505,11 @@ func (c *ctxtz) aclass(a *obj.Addr) int {
 			return C_GOTADDR
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SAUTO
@@ -512,6 +517,11 @@ func (c *ctxtz) aclass(a *obj.Addr) int {
 			return C_LAUTO
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + c.ctxt.FixedFrameSize()
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SAUTO
@@ -567,6 +577,11 @@ func (c *ctxtz) aclass(a *obj.Addr) int {
 			return C_SYMADDR
 
 		case obj.NAME_AUTO:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-SP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SACON
@@ -574,6 +589,11 @@ func (c *ctxtz) aclass(a *obj.Addr) int {
 			return C_LACON
 
 		case obj.NAME_PARAM:
+			if a.Reg == REGSP {
+				// unset base register for better printing, since
+				// a.Offset is still relative to pseudo-FP.
+				a.Reg = obj.REG_NONE
+			}
 			c.instoffset = int64(c.autosize) + a.Offset + c.ctxt.FixedFrameSize()
 			if c.instoffset >= -BIG && c.instoffset < BIG {
 				return C_SACON