[dev.typeparams] cmd/compile: make softfloat mode work with register ABI

Previously, softfloat mode does not work with register ABI, mainly
because the compiler doesn't know how to pass floating point
arguments and results. According to the ABI it should be passed in
FP registers, but there isn't any in softfloat mode.

This CL makes it work. When softfloat is used, we define the ABI
as having 0 floating point registers (because there aren't any).
The integer registers are unchanged. So floating point arguments
and results are passed in memory.

Another option is to pass (the bit representation of) floating
point values in integer registers. But this complicates things
because it'd need to reorder integer argument registers.

Change-Id: Ibecbeccb658c10a868fa7f2dcf75138f719cc809
Reviewed-on: https://go-review.googlesource.com/c/go/+/327274
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -160,9 +160,6 @@ func Main(archInit func(*ssagen.ArchInfo)) {
 		dwarf.EnableLogging(base.Debug.DwarfInl != 0)
 	}
 	if base.Debug.SoftFloat != 0 {
-		if buildcfg.Experiment.RegabiArgs {
-			log.Fatalf("softfloat mode with GOEXPERIMENT=regabiargs not implemented ")
-		}
 		ssagen.Arch.SoftFloat = true
 	}
 

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

@@ -171,7 +171,7 @@ type Frontend interface {
 }
 
 // NewConfig returns a new configuration object for the given architecture.
-func NewConfig(arch string, types Types, ctxt *obj.Link, optimize bool) *Config {
+func NewConfig(arch string, types Types, ctxt *obj.Link, optimize, softfloat bool) *Config {
 	c := &Config{arch: arch, Types: types}
 	c.useAvg = true
 	c.useHmul = true
@@ -320,6 +320,10 @@ func NewConfig(arch string, types Types, ctxt *obj.Link, optimize bool) *Config
 	c.optimize = optimize
 	c.useSSE = true
 	c.UseFMA = true
+	c.SoftFloat = softfloat
+	if softfloat {
+		c.floatParamRegs = nil // no FP registers in softfloat mode
+	}
 
 	c.ABI0 = abi.NewABIConfig(0, 0, ctxt.FixedFrameSize())
 	c.ABI1 = abi.NewABIConfig(len(c.intParamRegs), len(c.floatParamRegs), ctxt.FixedFrameSize())

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

@@ -215,7 +215,7 @@ func (x *expandState) isAlreadyExpandedAggregateType(t *types.Type) bool {
 		return false
 	}
 	return t.IsStruct() || t.IsArray() || t.IsComplex() || t.IsInterface() || t.IsString() || t.IsSlice() ||
-		t.Size() > x.regSize && t.IsInteger()
+		(t.Size() > x.regSize && (t.IsInteger() || (x.f.Config.SoftFloat && t.IsFloat())))
 }
 
 // offsetFrom creates an offset from a pointer, simplifying chained offsets and offsets from SP
@@ -380,6 +380,12 @@ func (x *expandState) rewriteSelect(leaf *Value, selector *Value, offset int64,
 		// The OpLoad was created to load the single field of the IData
 		// This case removes that StructSelect.
 		if leafType != selector.Type {
+			if x.f.Config.SoftFloat && selector.Type.IsFloat() {
+				if x.debug {
+					x.Printf("---OpLoad, break\n")
+				}
+				break // softfloat pass will take care of that
+			}
 			x.f.Fatalf("Unexpected Load as selector, leaf=%s, selector=%s\n", leaf.LongString(), selector.LongString())
 		}
 		leaf.copyOf(selector)
@@ -525,11 +531,11 @@ func (x *expandState) rewriteSelect(leaf *Value, selector *Value, offset int64,
 
 	case OpComplexReal:
 		ls := x.rewriteSelect(leaf, selector.Args[0], offset, regOffset)
-		locs = x.splitSlots(ls, ".real", 0, leafType)
+		locs = x.splitSlots(ls, ".real", 0, selector.Type)
 
 	case OpComplexImag:
-		ls := x.rewriteSelect(leaf, selector.Args[0], offset+leafType.Width, regOffset+RO_complex_imag) // result is FloatNN, width of result is offset of imaginary part.
-		locs = x.splitSlots(ls, ".imag", leafType.Width, leafType)
+		ls := x.rewriteSelect(leaf, selector.Args[0], offset+selector.Type.Width, regOffset+RO_complex_imag) // result is FloatNN, width of result is offset of imaginary part.
+		locs = x.splitSlots(ls, ".imag", selector.Type.Width, selector.Type)
 
 	case OpStringLen, OpSliceLen:
 		ls := x.rewriteSelect(leaf, selector.Args[0], offset+x.ptrSize, regOffset+RO_slice_len)

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

@@ -39,7 +39,7 @@ func testConfigArch(tb testing.TB, arch string) *Conf {
 		tb.Fatal("testTypes is 64-bit only")
 	}
 	c := &Conf{
-		config: NewConfig(arch, testTypes, ctxt, true),
+		config: NewConfig(arch, testTypes, ctxt, true, false),
 		tb:     tb,
 	}
 	return c

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

@@ -63,6 +63,7 @@ func softfloat(f *Func) {
 					v.Aux = f.Config.Types.UInt32
 				case 8:
 					v.Aux = f.Config.Types.UInt64
+					newInt64 = true
 				default:
 					v.Fatalf("bad float type with size %d", size)
 				}

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

@@ -87,8 +87,7 @@ func InitConfig() {
 	_ = types.NewPtr(types.Types[types.TINT64])                             // *int64
 	_ = types.NewPtr(types.ErrorType)                                       // *error
 	types.NewPtrCacheEnabled = false
-	ssaConfig = ssa.NewConfig(base.Ctxt.Arch.Name, *types_, base.Ctxt, base.Flag.N == 0)
-	ssaConfig.SoftFloat = Arch.SoftFloat
+	ssaConfig = ssa.NewConfig(base.Ctxt.Arch.Name, *types_, base.Ctxt, base.Flag.N == 0, Arch.SoftFloat)
 	ssaConfig.Race = base.Flag.Race
 	ssaCaches = make([]ssa.Cache, base.Flag.LowerC)
 
@@ -3653,6 +3652,16 @@ func softfloatInit() {
 // TODO: do not emit sfcall if operation can be optimized to constant in later
 // opt phase
 func (s *state) sfcall(op ssa.Op, args ...*ssa.Value) (*ssa.Value, bool) {
+	f2i := func(t *types.Type) *types.Type {
+		switch t.Kind() {
+		case types.TFLOAT32:
+			return types.Types[types.TUINT32]
+		case types.TFLOAT64:
+			return types.Types[types.TUINT64]
+		}
+		return t
+	}
+
 	if callDef, ok := softFloatOps[op]; ok {
 		switch op {
 		case ssa.OpLess32F,
@@ -3665,7 +3674,19 @@ func (s *state) sfcall(op ssa.Op, args ...*ssa.Value) (*ssa.Value, bool) {
 			args[1] = s.newValue1(s.ssaOp(ir.ONEG, types.Types[callDef.rtype]), args[1].Type, args[1])
 		}
 
-		result := s.rtcall(callDef.rtfn, true, []*types.Type{types.Types[callDef.rtype]}, args...)[0]
+		// runtime functions take uints for floats and returns uints.
+		// Convert to uints so we use the right calling convention.
+		for i, a := range args {
+			if a.Type.IsFloat() {
+				args[i] = s.newValue1(ssa.OpCopy, f2i(a.Type), a)
+			}
+		}
+
+		rt := types.Types[callDef.rtype]
+		result := s.rtcall(callDef.rtfn, true, []*types.Type{f2i(rt)}, args...)[0]
+		if rt.IsFloat() {
+			result = s.newValue1(ssa.OpCopy, rt, result)
+		}
 		if op == ssa.OpNeq32F || op == ssa.OpNeq64F {
 			result = s.newValue1(ssa.OpNot, result.Type, result)
 		}

test/fixedbugs/issue26163.go

@@ -1,4 +1,4 @@
-// compile -N -d=softfloat -goexperiment noregabiargs
+// compile -N -d=softfloat
 
 // Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style

test/fixedbugs/issue28688.go

@@ -1,4 +1,4 @@
-// run -gcflags=-d=softfloat -goexperiment noregabiargs
+// run -gcflags=-d=softfloat
 
 // Copyright 2018 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style