cmd/compile: fix constant conversion involving complex types
In CL 187657, I refactored constant conversion logic without realizing
that conversions between int/float and complex types are allowed for
constants (assuming the constant values are representable by the
destination type), but are never allowed for non-constant expressions.
This CL expands convertop to take an extra srcConstant parameter to
indicate whether the source expression is a constant; and if so, to
allow any numeric-to-numeric conversion. (Conversions of values that
cannot be represented in the destination type are rejected by
evconst.)
Fixes #38117.
Change-Id: Id7077d749a14c8fd910be38da170fa5254819f2b
Reviewed-on: https://go-review.googlesource.com/c/go/+/226197
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/src/cmd/compile/internal/gc/subr.go b/src/cmd/compile/internal/gc/subr.go
index 0a2a116..7c1ab89 100644
--- a/src/cmd/compile/internal/gc/subr.go
+++ b/src/cmd/compile/internal/gc/subr.go
@@ -542,7 +542,7 @@
// Is type src assignment compatible to type dst?
// If so, return op code to use in conversion.
// If not, return OXXX.
-func assignop(src *types.Type, dst *types.Type, why *string) Op {
+func assignop(src, dst *types.Type, why *string) Op {
if why != nil {
*why = ""
}
@@ -665,7 +665,8 @@
// Can we convert a value of type src to a value of type dst?
// If so, return op code to use in conversion (maybe OCONVNOP).
// If not, return OXXX.
-func convertop(src *types.Type, dst *types.Type, why *string) Op {
+// srcConstant indicates whether the value of type src is a constant.
+func convertop(srcConstant bool, src, dst *types.Type, why *string) Op {
if why != nil {
*why = ""
}
@@ -741,6 +742,13 @@
return OCONV
}
+ // Special case for constant conversions: any numeric
+ // conversion is potentially okay. We'll validate further
+ // within evconst. See #38117.
+ if srcConstant && (src.IsInteger() || src.IsFloat() || src.IsComplex()) && (dst.IsInteger() || dst.IsFloat() || dst.IsComplex()) {
+ return OCONV
+ }
+
// 6. src is an integer or has type []byte or []rune
// and dst is a string type.
if src.IsInteger() && dst.IsString() {
diff --git a/src/cmd/compile/internal/gc/typecheck.go b/src/cmd/compile/internal/gc/typecheck.go
index 2ca7f2d..6e04908 100644
--- a/src/cmd/compile/internal/gc/typecheck.go
+++ b/src/cmd/compile/internal/gc/typecheck.go
@@ -1634,7 +1634,7 @@
return n
}
var why string
- n.Op = convertop(t, n.Type, &why)
+ n.Op = convertop(n.Left.Op == OLITERAL, t, n.Type, &why)
if n.Op == 0 {
if !n.Diag() && !n.Type.Broke() && !n.Left.Diag() {
yyerror("cannot convert %L to type %v%s", n.Left, n.Type, why)
diff --git a/test/fixedbugs/issue38117.go b/test/fixedbugs/issue38117.go
new file mode 100644
index 0000000..11edef7
--- /dev/null
+++ b/test/fixedbugs/issue38117.go
@@ -0,0 +1,17 @@
+// errorcheck
+
+// Copyright 2020 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.
+
+// cmd/compile erroneously rejected conversions of constant values
+// between int/float and complex types.
+
+package p
+
+const (
+ _ = int(complex64(int(0)))
+ _ = float64(complex128(float64(0)))
+
+ _ = int8(complex128(1000)) // ERROR "overflow"
+)
