[dev.typeparams] cmd/compile: fix export/import of constants with typeparam type

A constant will have a TYPEPARAM type if it appears in a place where it
must match that typeparam type (e.g. in a binary operation with a
variable of that typeparam type). If so, then we must write out its
actual constant kind as well, so its constant val can be read in
properly during import.

Fixed some export/import tests which were casting some untyped constants
to avoid this problem.

Change-Id: I285ad8f1c8febbe526769c96e6b27acbd23050f0
Reviewed-on: https://go-review.googlesource.com/c/go/+/324189
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

1 files changed, 24 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/typecheck/iimport.go b/src/cmd/compile/internal/typecheck/iimport.go
index 4c31e47378..96107b657b 100644
--- a/src/cmd/compile/internal/typecheck/iimport.go
+++ b/src/cmd/compile/internal/typecheck/iimport.go
@@ -400,19 +400,39 @@ func (r *importReader) doDecl(sym *types.Sym) *ir.Name {
 }
 
 func (p *importReader) value(typ *types.Type) constant.Value {
-	switch constTypeOf(typ) {
+	var kind constant.Kind
+	var valType *types.Type
+
+	if typ.Kind() == types.TTYPEPARAM {
+		// If a constant had a typeparam type, then we wrote out its
+		// actual constant kind as well.
+		kind = constant.Kind(p.int64())
+		switch kind {
+		case constant.Int:
+			valType = types.Types[types.TINT64]
+		case constant.Float:
+			valType = types.Types[types.TFLOAT64]
+		case constant.Complex:
+			valType = types.Types[types.TCOMPLEX128]
+		}
+	} else {
+		kind = constTypeOf(typ)
+		valType = typ
+	}
+
+	switch kind {
 	case constant.Bool:
 		return constant.MakeBool(p.bool())
 	case constant.String:
 		return constant.MakeString(p.string())
 	case constant.Int:
 		var i big.Int
-		p.mpint(&i, typ)
+		p.mpint(&i, valType)
 		return constant.Make(&i)
 	case constant.Float:
-		return p.float(typ)
+		return p.float(valType)
 	case constant.Complex:
-		return makeComplex(p.float(typ), p.float(typ))
+		return makeComplex(p.float(valType), p.float(valType))
 	}
 
 	base.Fatalf("unexpected value type: %v", typ)