cmd/compile: add "surprised by IData of Arg" case for register args

This fixes a compile crash for
GOEXPERIMENT=regabi,regabiargs go test -c  go/constant

Updates #40724.

Change-Id: I238cef436e045647815326fc8fdb025c30ba1f5c
Reviewed-on: https://go-review.googlesource.com/c/go/+/307309
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>

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

@@ -317,6 +317,15 @@ func (x *expandState) rewriteSelect(leaf *Value, selector *Value, offset int64,
 		}
 	}
 	switch selector.Op {
+	case OpArgIntReg, OpArgFloatReg:
+		if leafType == selector.Type { // OpIData leads us here, sometimes.
+			leaf.copyOf(selector)
+		} else {
+			x.f.Fatalf("Unexpected %s type, selector=%s, leaf=%s\n", selector.Op.String(), selector.LongString(), leaf.LongString())
+		}
+		if x.debug {
+			x.Printf("---%s, break\n", selector.Op.String())
+		}
 	case OpArg:
 		if !x.isAlreadyExpandedAggregateType(selector.Type) {
 			if leafType == selector.Type { // OpIData leads us here, sometimes.

test/abi/idata.go

@@ -0,0 +1,97 @@
+// run
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Excerpted from go/constant/value.go to capture a bug from there.
+
+package main
+
+import (
+	"fmt"
+	"math"
+	"math/big"
+)
+
+type (
+	unknownVal struct{}
+	intVal     struct{ val *big.Int }   // Int values not representable as an int64
+	ratVal     struct{ val *big.Rat }   // Float values representable as a fraction
+	floatVal   struct{ val *big.Float } // Float values not representable as a fraction
+	complexVal struct{ re, im Value }
+)
+
+const prec = 512
+
+func (unknownVal) String() string { return "unknown" }
+
+func (x intVal) String() string   { return x.val.String() }
+func (x ratVal) String() string   { return rtof(x).String() }
+
+func (x floatVal) String() string {
+	f := x.val
+
+	// Use exact fmt formatting if in float64 range (common case):
+	// proceed if f doesn't underflow to 0 or overflow to inf.
+	if x, _ := f.Float64(); f.Sign() == 0 == (x == 0) && !math.IsInf(x, 0) {
+		return fmt.Sprintf("%.6g", x)
+	}
+
+	return "OOPS"
+}
+
+func (x complexVal) String() string { return fmt.Sprintf("(%s + %si)", x.re, x.im) }
+
+func newFloat() *big.Float { return new(big.Float).SetPrec(prec) }
+
+//go:noinline
+//go:registerparams
+func itor(x intVal) ratVal       { return ratVal{nil} }
+
+//go:noinline
+//go:registerparams
+func itof(x intVal) floatVal     { return floatVal{nil} }
+func rtof(x ratVal) floatVal     { return floatVal{newFloat().SetRat(x.val)} }
+
+type Value interface {
+	String() string
+}
+
+//go:noinline
+//go:registerparams
+func ToFloat(x Value) Value {
+	switch x := x.(type) {
+	case intVal:
+		if smallInt(x.val) {
+			return itor(x)
+		}
+		return itof(x)
+	case ratVal, floatVal:
+		return x
+	case complexVal:
+		if Sign(x.im) == 0 {
+			return ToFloat(x.re)
+		}
+	}
+	return unknownVal{}
+}
+
+//go:noinline
+//go:registerparams
+func smallInt(x *big.Int) bool {
+	return false
+}
+
+//go:noinline
+//go:registerparams
+func Sign(x Value) int {
+	return 0
+}
+
+
+func main() {
+	v := ratVal{big.NewRat(22,7)}
+	s := ToFloat(v).String()
+	fmt.Printf("s=%s\n", s)
+}

test/abi/idata.out

@@ -0,0 +1 @@
+s=3.14286