cmd/compile: plumb abi info into ssagen/ssa

Plumb abi information into ssa/ssagen for plain calls
and plain functions (not methods).  Does not extend all the
way through the compiler (yet).

One test disabled because it extends far enough to break the test.

Normalized all the compiler's register args TODOs to
// TODO(register args) ...

For #40724.

Change-Id: I0173a4579f032ac3c9db3aef1749d40da5ea01ff
Reviewed-on: https://go-review.googlesource.com/c/go/+/293389
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

11 files changed, 134 insertions, 51 deletions

diff --git a/src/cmd/compile/internal/abi/abiutils.go b/src/cmd/compile/internal/abi/abiutils.go
index e935821802..7b388ec3dc 100644
--- a/src/cmd/compile/internal/abi/abiutils.go
+++ b/src/cmd/compile/internal/abi/abiutils.go
@@ -116,6 +116,13 @@ func NewABIConfig(iRegsCount, fRegsCount int) *ABIConfig {
 	return &ABIConfig{regAmounts: RegAmounts{iRegsCount, fRegsCount}, regsForTypeCache: make(map[*types.Type]int)}
 }
 
+// Copy returns a copy of an ABIConfig for use in a function's compilation so that access to the cache does not need to be protected with a mutex.
+func (a *ABIConfig) Copy() *ABIConfig {
+	b := *a
+	b.regsForTypeCache = make(map[*types.Type]int)
+	return &b
+}
+
 // NumParamRegs returns the number of parameter registers used for a given type,
 // without regard for the number available.
 func (a *ABIConfig) NumParamRegs(t *types.Type) int {
@@ -157,12 +164,12 @@ func (a *ABIConfig) NumParamRegs(t *types.Type) int {
 // 'config' and analyzes the function to determine how its parameters
 // and results will be passed (in registers or on the stack), returning
 // an ABIParamResultInfo object that holds the results of the analysis.
-func (config *ABIConfig) ABIAnalyze(t *types.Type) ABIParamResultInfo {
+func (config *ABIConfig) ABIAnalyze(t *types.Type) *ABIParamResultInfo {
 	setup()
 	s := assignState{
 		rTotal: config.regAmounts,
 	}
-	result := ABIParamResultInfo{config: config}
+	result := &ABIParamResultInfo{config: config}
 
 	// Receiver
 	ft := t.FuncType()
diff --git a/src/cmd/compile/internal/ir/node.go b/src/cmd/compile/internal/ir/node.go
index 59643713fa..38f9123582 100644
--- a/src/cmd/compile/internal/ir/node.go
+++ b/src/cmd/compile/internal/ir/node.go
@@ -456,7 +456,7 @@ const (
 	// Go command pragmas
 	GoBuildPragma
 
-	RegisterParams // TODO remove after register abi is working
+	RegisterParams // TODO(register args) remove after register abi is working
 
 )
 
diff --git a/src/cmd/compile/internal/noder/lex.go b/src/cmd/compile/internal/noder/lex.go
index cdca9e55f3..36cfb9bc23 100644
--- a/src/cmd/compile/internal/noder/lex.go
+++ b/src/cmd/compile/internal/noder/lex.go
@@ -28,7 +28,7 @@ const (
 		ir.Nosplit |
 		ir.Noinline |
 		ir.NoCheckPtr |
-		ir.RegisterParams | // TODO remove after register abi is working
+		ir.RegisterParams | // TODO(register args) remove after register abi is working
 		ir.CgoUnsafeArgs |
 		ir.UintptrEscapes |
 		ir.Systemstack |
@@ -80,7 +80,7 @@ func pragmaFlag(verb string) ir.PragmaFlag {
 		// in the argument list.
 		// Used in syscall/dll_windows.go.
 		return ir.UintptrEscapes
-	case "go:registerparams": // TODO remove after register abi is working
+	case "go:registerparams": // TODO(register args) remove after register abi is working
 		return ir.RegisterParams
 	case "go:notinheap":
 		return ir.NotInHeap
diff --git a/src/cmd/compile/internal/ssa/func.go b/src/cmd/compile/internal/ssa/func.go
index de99a8d4af..a36529af03 100644
--- a/src/cmd/compile/internal/ssa/func.go
+++ b/src/cmd/compile/internal/ssa/func.go
@@ -5,6 +5,7 @@
 package ssa
 
 import (
+	"cmd/compile/internal/abi"
 	"cmd/compile/internal/types"
 	"cmd/internal/src"
 	"crypto/sha1"
@@ -43,6 +44,10 @@ type Func struct {
 	DebugTest      bool           // default true unless $GOSSAHASH != ""; as a debugging aid, make new code conditional on this and use GOSSAHASH to binary search for failing cases
 	PrintOrHtmlSSA bool           // true if GOSSAFUNC matches, true even if fe.Log() (spew phase results to stdout) is false.
 	ruleMatches    map[string]int // number of times countRule was called during compilation for any given string
+	ABI0           *abi.ABIConfig // A copy, for no-sync access
+	ABI1           *abi.ABIConfig // A copy, for no-sync access
+	ABISelf        *abi.ABIConfig // ABI for function being compiled
+	ABIDefault     *abi.ABIConfig // ABI for rtcall and other no-parsed-signature/pragma functions.
 
 	scheduled   bool  // Values in Blocks are in final order
 	laidout     bool  // Blocks are ordered
diff --git a/src/cmd/compile/internal/ssa/loopreschedchecks.go b/src/cmd/compile/internal/ssa/loopreschedchecks.go
index 9c73bcff26..5308d1ac48 100644
--- a/src/cmd/compile/internal/ssa/loopreschedchecks.go
+++ b/src/cmd/compile/internal/ssa/loopreschedchecks.go
@@ -246,7 +246,8 @@ func insertLoopReschedChecks(f *Func) {
 		//    mem1 := call resched (mem0)
 		//    goto header
 		resched := f.fe.Syslook("goschedguarded")
-		mem1 := sched.NewValue1A(bb.Pos, OpStaticCall, types.TypeMem, StaticAuxCall(resched, nil, nil), mem0)
+		// TODO(register args) -- will need more details
+		mem1 := sched.NewValue1A(bb.Pos, OpStaticCall, types.TypeMem, StaticAuxCall(resched, nil, nil, nil), mem0)
 		sched.AddEdgeTo(h)
 		headerMemPhi.AddArg(mem1)
 
diff --git a/src/cmd/compile/internal/ssa/op.go b/src/cmd/compile/internal/ssa/op.go
index cf0d2affc7..4bda7369bb 100644
--- a/src/cmd/compile/internal/ssa/op.go
+++ b/src/cmd/compile/internal/ssa/op.go
@@ -5,6 +5,7 @@
 package ssa
 
 import (
+	"cmd/compile/internal/abi"
 	"cmd/compile/internal/ir"
 	"cmd/compile/internal/types"
 	"cmd/internal/obj"
@@ -71,15 +72,18 @@ type auxType int8
 
 type Param struct {
 	Type   *types.Type
-	Offset int32    // Offset of Param if not in a register.
+	Offset int32 // Offset of Param if not in a register, spill offset if it is in a register input, types.BADWIDTH if it is a register output.
+	Reg    []abi.RegIndex
 	Name   *ir.Name // For OwnAux, need to prepend stores with Vardefs
 }
 
 type AuxCall struct {
+	// TODO(register args) this information is largely redundant with ../abi information, needs cleanup once new ABI is in place.
 	Fn      *obj.LSym
 	args    []Param // Includes receiver for method calls.  Does NOT include hidden closure pointer.
 	results []Param
-	reg     *regInfo // regInfo for this call // TODO for now nil means ignore
+	reg     *regInfo                // regInfo for this call // TODO for now nil means ignore
+	abiInfo *abi.ABIParamResultInfo // TODO remove fields above redundant with this information.
 }
 
 // ResultForOffset returns the index of the result at a particular offset among the results
@@ -186,9 +190,9 @@ func (a *AuxCall) String() string {
 }
 
 // StaticAuxCall returns an AuxCall for a static call.
-func StaticAuxCall(sym *obj.LSym, args []Param, results []Param) *AuxCall {
+func StaticAuxCall(sym *obj.LSym, args []Param, results []Param, paramResultInfo *abi.ABIParamResultInfo) *AuxCall {
 	// TODO Create regInfo for AuxCall
-	return &AuxCall{Fn: sym, args: args, results: results}
+	return &AuxCall{Fn: sym, args: args, results: results, abiInfo: paramResultInfo}
 }
 
 // InterfaceAuxCall returns an AuxCall for an interface call.
@@ -206,9 +210,10 @@ func ClosureAuxCall(args []Param, results []Param) *AuxCall {
 func (*AuxCall) CanBeAnSSAAux() {}
 
 // OwnAuxCall returns a function's own AuxCall
-func OwnAuxCall(fn *obj.LSym, args []Param, results []Param) *AuxCall {
+
+func OwnAuxCall(fn *obj.LSym, args []Param, results []Param, paramResultInfo *abi.ABIParamResultInfo) *AuxCall {
 	// TODO if this remains identical to ClosureAuxCall above after new ABI is done, should deduplicate.
-	return &AuxCall{Fn: fn, args: args, results: results}
+	return &AuxCall{Fn: fn, args: args, results: results, abiInfo: paramResultInfo}
 }
 
 const (
diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index e82aa84cdf..ac6278ab9d 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -765,7 +765,7 @@ func devirt(v *Value, aux Aux, sym Sym, offset int64) *AuxCall {
 		return nil
 	}
 	va := aux.(*AuxCall)
-	return StaticAuxCall(lsym, va.args, va.results)
+	return StaticAuxCall(lsym, va.args, va.results, va.abiInfo)
 }
 
 // de-virtualize an InterLECall
diff --git a/src/cmd/compile/internal/ssa/writebarrier.go b/src/cmd/compile/internal/ssa/writebarrier.go
index 4378f2d627..7d375da128 100644
--- a/src/cmd/compile/internal/ssa/writebarrier.go
+++ b/src/cmd/compile/internal/ssa/writebarrier.go
@@ -512,7 +512,8 @@ func wbcall(pos src.XPos, b *Block, fn, typ *obj.LSym, ptr, val, mem, sp, sb *Va
 	off = round(off, config.PtrSize)
 
 	// issue call
-	mem = b.NewValue1A(pos, OpStaticCall, types.TypeMem, StaticAuxCall(fn, ACArgs, nil), mem)
+	// TODO(register args) -- will need more details
+	mem = b.NewValue1A(pos, OpStaticCall, types.TypeMem, StaticAuxCall(fn, ACArgs, nil, nil), mem)
 	mem.AuxInt = off - config.ctxt.FixedFrameSize()
 	return mem
 }
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index cfc54ae0ab..d69eb17ca9 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -357,7 +357,20 @@ func buildssa(fn *ir.Func, worker int) *ssa.Func {
 	if fn.Pragma&ir.Nosplit != 0 {
 		s.f.NoSplit = true
 	}
-	if fn.Pragma&ir.RegisterParams != 0 { // TODO remove after register abi is working
+	s.f.ABI0 = ssaConfig.ABI0.Copy() // Make a copy to avoid racy map operations in type-width cache.
+	s.f.ABI1 = ssaConfig.ABI1.Copy()
+
+	s.f.ABIDefault = s.f.ABI1 // Default ABI for function calls with no parsed signature for a pragma, e.g. rtcall
+	// TODO(register args) -- remove "true ||"; in the short run, turning on the register ABI experiment still leaves the compiler defaulting to ABI0.
+	// TODO(register args) -- remove this conditional entirely when register ABI is not an experiment.
+	if true || objabi.Regabi_enabled == 0 {
+		s.f.ABIDefault = s.f.ABI0 // reset
+	}
+
+	s.f.ABISelf = s.f.ABIDefault
+
+	if fn.Pragma&ir.RegisterParams != 0 { // TODO(register args) remove after register abi is working
+		s.f.ABISelf = s.f.ABI1
 		if strings.Contains(name, ".") {
 			base.ErrorfAt(fn.Pos(), "Calls to //go:registerparams method %s won't work, remove the pragma from the declaration.", name)
 		}
@@ -449,18 +462,19 @@ func buildssa(fn *ir.Func, worker int) *ssa.Func {
 		s.vars[memVar] = s.newValue1Apos(ssa.OpVarLive, types.TypeMem, deferBitsTemp, s.mem(), false)
 	}
 
+	params := s.f.ABISelf.ABIAnalyze(fn.Type())
+
 	// Generate addresses of local declarations
 	s.decladdrs = map[*ir.Name]*ssa.Value{}
-	var args []ssa.Param
 	var results []ssa.Param
 	for _, n := range fn.Dcl {
 		switch n.Class {
 		case ir.PPARAM:
+			// Be aware that blank and unnamed input parameters will not appear here, but do appear in the type
 			s.decladdrs[n] = s.entryNewValue2A(ssa.OpLocalAddr, types.NewPtr(n.Type()), n, s.sp, s.startmem)
-			args = append(args, ssa.Param{Type: n.Type(), Offset: int32(n.FrameOffset())})
 		case ir.PPARAMOUT:
 			s.decladdrs[n] = s.entryNewValue2A(ssa.OpLocalAddr, types.NewPtr(n.Type()), n, s.sp, s.startmem)
-			results = append(results, ssa.Param{Type: n.Type(), Offset: int32(n.FrameOffset()), Name: n})
+			results = append(results, ssa.Param{Name: n})
 		case ir.PAUTO:
 			// processed at each use, to prevent Addr coming
 			// before the decl.
@@ -468,7 +482,36 @@ func buildssa(fn *ir.Func, worker int) *ssa.Func {
 			s.Fatalf("local variable with class %v unimplemented", n.Class)
 		}
 	}
-	s.f.OwnAux = ssa.OwnAuxCall(fn.LSym, args, results)
+
+	// TODO: figure out why base.Ctxt.FixedFrameSize() is not added to these offsets here (compare to calls).
+	// The input half is ignored unless a register ABI is used.
+	var args []ssa.Param
+	for _, p := range params.InParams() {
+		r := p.Registers
+		var o int32
+		if len(r) == 0 {
+			o = p.Offset()
+		} else {
+			o = p.SpillOffset() + int32(params.SpillAreaOffset())
+		}
+		args = append(args, ssa.Param{Type: p.Type, Offset: o, Reg: r})
+	}
+
+	// For now, need the ir.Name attached to these, so update those already created.
+	for i, p := range params.OutParams() {
+		r := p.Registers
+		var o int32
+		if len(r) == 0 {
+			o = p.Offset()
+		} else {
+			o = types.BADWIDTH
+		}
+		results[i].Type = p.Type
+		results[i].Offset = o
+		results[i].Reg = r
+	}
+
+	s.f.OwnAux = ssa.OwnAuxCall(fn.LSym, args, results, params)
 
 	// Populate SSAable arguments.
 	for _, n := range fn.Dcl {
@@ -1846,7 +1889,7 @@ func (s *state) exit() *ssa.Block {
 		}
 
 		// Run exit code. Today, this is just racefuncexit, in -race mode.
-		// TODO this seems risky here with a register-ABI, but not clear it is right to do it earlier either.
+		// TODO(register args) this seems risky here with a register-ABI, but not clear it is right to do it earlier either.
 		// Spills in register allocation might just fix it.
 		s.stmtList(s.curfn.Exit)
 
@@ -4691,7 +4734,7 @@ func (s *state) openDeferExit() {
 			aux := ssa.ClosureAuxCall(ACArgs, ACResults)
 			call = s.newValue2A(ssa.OpClosureLECall, aux.LateExpansionResultType(), aux, codeptr, v)
 		} else {
-			aux := ssa.StaticAuxCall(fn.(*ir.Name).Linksym(), ACArgs, ACResults)
+			aux := ssa.StaticAuxCall(fn.(*ir.Name).Linksym(), ACArgs, ACResults, nil) // TODO will need types for this.
 			call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
 		}
 		callArgs = append(callArgs, s.mem())
@@ -4738,18 +4781,9 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 	var codeptr *ssa.Value // ptr to target code (if dynamic)
 	var rcvr *ssa.Value    // receiver to set
 	fn := n.X
-	var ACArgs []ssa.Param
-	var ACResults []ssa.Param
-	var callArgs []*ssa.Value
-	res := n.X.Type().Results()
-	if k == callNormal {
-		nf := res.NumFields()
-		for i := 0; i < nf; i++ {
-			fp := res.Field(i)
-			ACResults = append(ACResults, ssa.Param{Type: fp.Type, Offset: int32(fp.Offset + base.Ctxt.FixedFrameSize())})
-		}
-	}
-
+	var ACArgs []ssa.Param    // AuxCall args
+	var ACResults []ssa.Param // AuxCall results
+	var callArgs []*ssa.Value // For late-expansion, the args themselves (not stored, args to the call instead).
 	inRegisters := false
 
 	switch n.Op() {
@@ -4757,7 +4791,7 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		if k == callNormal && fn.Op() == ir.ONAME && fn.(*ir.Name).Class == ir.PFUNC {
 			fn := fn.(*ir.Name)
 			callee = fn
-			// TODO remove after register abi is working
+			// TODO(register args) remove after register abi is working
 			inRegistersImported := fn.Pragma()&ir.RegisterParams != 0
 			inRegistersSamePackage := fn.Func != nil && fn.Func.Pragma&ir.RegisterParams != 0
 			inRegisters = inRegistersImported || inRegistersSamePackage
@@ -4790,6 +4824,27 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 	types.CalcSize(fn.Type())
 	stksize := fn.Type().ArgWidth() // includes receiver, args, and results
 
+	abi := s.f.ABI1
+	if !inRegisters {
+		abi = s.f.ABI0
+	}
+
+	params := abi.ABIAnalyze(n.X.Type())
+
+	res := n.X.Type().Results()
+	if k == callNormal {
+		for _, p := range params.OutParams() {
+			r := p.Registers
+			var o int32
+			if len(r) == 0 {
+				o = p.Offset()
+			} else {
+				o = p.SpillOffset() + int32(params.SpillAreaOffset())
+			}
+			ACResults = append(ACResults, ssa.Param{Type: p.Type, Offset: o + int32(base.Ctxt.FixedFrameSize()), Reg: r})
+		}
+	}
+
 	var call *ssa.Value
 	if k == callDeferStack {
 		// Make a defer struct d on the stack.
@@ -4841,14 +4896,14 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 
 		// Call runtime.deferprocStack with pointer to _defer record.
 		ACArgs = append(ACArgs, ssa.Param{Type: types.Types[types.TUINTPTR], Offset: int32(base.Ctxt.FixedFrameSize())})
-		aux := ssa.StaticAuxCall(ir.Syms.DeferprocStack, ACArgs, ACResults)
+		aux := ssa.StaticAuxCall(ir.Syms.DeferprocStack, ACArgs, ACResults, nil)
 		callArgs = append(callArgs, addr, s.mem())
 		call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
 		call.AddArgs(callArgs...)
 		if stksize < int64(types.PtrSize) {
 			// We need room for both the call to deferprocStack and the call to
 			// the deferred function.
-			// TODO Revisit this if/when we pass args in registers.
+			// TODO(register args) Revisit this if/when we pass args in registers.
 			stksize = int64(types.PtrSize)
 		}
 		call.AuxInt = stksize
@@ -4870,7 +4925,7 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 
 		// Set receiver (for interface calls).
 		if rcvr != nil {
-			ACArgs = append(ACArgs, ssa.Param{Type: types.Types[types.TUINTPTR], Offset: int32(argStart)})
+			// ACArgs = append(ACArgs, ssa.Param{Type: types.Types[types.TUINTPTR], Offset: int32(argStart)})
 			callArgs = append(callArgs, rcvr)
 		}
 
@@ -4880,11 +4935,20 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		if n.Op() == ir.OCALLMETH {
 			base.Fatalf("OCALLMETH missed by walkCall")
 		}
-		for i, n := range args {
-			f := t.Params().Field(i)
-			ACArg, arg := s.putArg(n, f.Type, argStart+f.Offset)
+
+		for _, p := range params.InParams() {
+			r := p.Registers
+			var o int32
+			if len(r) == 0 {
+				o = p.Offset()
+			} else {
+				o = p.SpillOffset() + int32(params.SpillAreaOffset())
+			}
+			ACArg := ssa.Param{Type: p.Type, Offset: int32(argStart) + o, Reg: r}
 			ACArgs = append(ACArgs, ACArg)
-			callArgs = append(callArgs, arg)
+		}
+		for i, n := range args {
+			callArgs = append(callArgs, s.putArg(n, t.Params().Field(i).Type))
 		}
 
 		callArgs = append(callArgs, s.mem())
@@ -4892,11 +4956,11 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		// call target
 		switch {
 		case k == callDefer:
-			aux := ssa.StaticAuxCall(ir.Syms.Deferproc, ACArgs, ACResults)
+			aux := ssa.StaticAuxCall(ir.Syms.Deferproc, ACArgs, ACResults, nil) // TODO paramResultInfo for DeferProc
 			call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
 		case k == callGo:
-			aux := ssa.StaticAuxCall(ir.Syms.Newproc, ACArgs, ACResults)
-			call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
+			aux := ssa.StaticAuxCall(ir.Syms.Newproc, ACArgs, ACResults, nil)
+			call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux) // TODO paramResultInfo for NewProc
 		case closure != nil:
 			// rawLoad because loading the code pointer from a
 			// closure is always safe, but IsSanitizerSafeAddr
@@ -4910,7 +4974,7 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 			aux := ssa.InterfaceAuxCall(ACArgs, ACResults)
 			call = s.newValue1A(ssa.OpInterLECall, aux.LateExpansionResultType(), aux, codeptr)
 		case callee != nil:
-			aux := ssa.StaticAuxCall(callTargetLSym(callee, s.curfn.LSym), ACArgs, ACResults)
+			aux := ssa.StaticAuxCall(callTargetLSym(callee, s.curfn.LSym), ACArgs, ACResults, params)
 			call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
 		default:
 			s.Fatalf("bad call type %v %v", n.Op(), n)
@@ -5391,7 +5455,7 @@ func (s *state) rtcall(fn *obj.LSym, returns bool, results []*types.Type, args .
 
 	// Issue call
 	var call *ssa.Value
-	aux := ssa.StaticAuxCall(fn, ACArgs, ACResults)
+	aux := ssa.StaticAuxCall(fn, ACArgs, ACResults, nil) // WILL NEED A TYPE FOR THIS.)
 	callArgs = append(callArgs, s.mem())
 	call = s.newValue0A(ssa.OpStaticLECall, aux.LateExpansionResultType(), aux)
 	call.AddArgs(callArgs...)
@@ -5539,15 +5603,15 @@ func (s *state) storeTypePtrs(t *types.Type, left, right *ssa.Value) {
 	}
 }
 
-// putArg evaluates n for the purpose of passing it as an argument to a function and returns the corresponding Param and value for the call.
-func (s *state) putArg(n ir.Node, t *types.Type, off int64) (ssa.Param, *ssa.Value) {
+// putArg evaluates n for the purpose of passing it as an argument to a function and returns the value for the call.
+func (s *state) putArg(n ir.Node, t *types.Type) *ssa.Value {
 	var a *ssa.Value
 	if !TypeOK(t) {
 		a = s.newValue2(ssa.OpDereference, t, s.addr(n), s.mem())
 	} else {
 		a = s.expr(n)
 	}
-	return ssa.Param{Type: t, Offset: int32(off)}, a
+	return a
 }
 
 func (s *state) storeArgWithBase(n ir.Node, t *types.Type, base *ssa.Value, off int64) {
diff --git a/src/cmd/compile/internal/typecheck/iexport.go b/src/cmd/compile/internal/typecheck/iexport.go
index 6fab74e61f..38ac753201 100644
--- a/src/cmd/compile/internal/typecheck/iexport.go
+++ b/src/cmd/compile/internal/typecheck/iexport.go
@@ -1025,7 +1025,7 @@ func (w *exportWriter) funcExt(n *ir.Name) {
 	w.linkname(n.Sym())
 	w.symIdx(n.Sym())
 
-	// TODO remove after register abi is working.
+	// TODO(register args) remove after register abi is working.
 	w.uint64(uint64(n.Func.Pragma))
 
 	// Escape analysis.
diff --git a/src/cmd/compile/internal/typecheck/iimport.go b/src/cmd/compile/internal/typecheck/iimport.go
index 29090a9178..17aa35549d 100644
--- a/src/cmd/compile/internal/typecheck/iimport.go
+++ b/src/cmd/compile/internal/typecheck/iimport.go
@@ -673,7 +673,7 @@ func (r *importReader) funcExt(n *ir.Name) {
 	r.linkname(n.Sym())
 	r.symIdx(n.Sym())
 
-	// TODO remove after register abi is working
+	// TODO(register args) remove after register abi is working
 	n.SetPragma(ir.PragmaFlag(r.uint64()))
 
 	// Escape analysis.