[release-branch.go1.20] cmd/compile: remove constant arithmetic overflows during typecheck

Since go1.19, these errors are already reported by types2 for any user's
Go code. Compiler generated code, which looks like constant expression
should be evaluated as non-constant semantic, which allows overflows.

Fixes #58319

Change-Id: I6f0049a69bdb0a8d0d7a0db49c7badaa92598ea2
Reviewed-on: https://go-review.googlesource.com/c/go/+/466676
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

2 files changed, 15 insertions, 34 deletions

diff --git a/src/cmd/compile/internal/typecheck/const.go b/src/cmd/compile/internal/typecheck/const.go
index edc399ffd7..6855f05b7b 100644
--- a/src/cmd/compile/internal/typecheck/const.go
+++ b/src/cmd/compile/internal/typecheck/const.go
@@ -34,10 +34,7 @@ func roundFloat(v constant.Value, sz int64) constant.Value {
 // truncate float literal fv to 32-bit or 64-bit precision
 // according to type; return truncated value.
 func truncfltlit(v constant.Value, t *types.Type) constant.Value {
-	if t.IsUntyped() || overflow(v, t) {
-		// If there was overflow, simply continuing would set the
-		// value to Inf which in turn would lead to spurious follow-on
-		// errors. Avoid this by returning the existing value.
+	if t.IsUntyped() {
 		return v
 	}
 
@@ -48,10 +45,7 @@ func truncfltlit(v constant.Value, t *types.Type) constant.Value {
 // precision, according to type; return truncated value. In case of
 // overflow, calls Errorf but does not truncate the input value.
 func trunccmplxlit(v constant.Value, t *types.Type) constant.Value {
-	if t.IsUntyped() || overflow(v, t) {
-		// If there was overflow, simply continuing would set the
-		// value to Inf which in turn would lead to spurious follow-on
-		// errors. Avoid this by returning the existing value.
+	if t.IsUntyped() {
 		return v
 	}
 
@@ -251,7 +245,6 @@ func convertVal(v constant.Value, t *types.Type, explicit bool) constant.Value {
 		switch {
 		case t.IsInteger():
 			v = toint(v)
-			overflow(v, t)
 			return v
 		case t.IsFloat():
 			v = toflt(v)
@@ -273,9 +266,6 @@ func tocplx(v constant.Value) constant.Value {
 
 func toflt(v constant.Value) constant.Value {
 	if v.Kind() == constant.Complex {
-		if constant.Sign(constant.Imag(v)) != 0 {
-			base.Errorf("constant %v truncated to real", v)
-		}
 		v = constant.Real(v)
 	}
 
@@ -284,9 +274,6 @@ func toflt(v constant.Value) constant.Value {
 
 func toint(v constant.Value) constant.Value {
 	if v.Kind() == constant.Complex {
-		if constant.Sign(constant.Imag(v)) != 0 {
-			base.Errorf("constant %v truncated to integer", v)
-		}
 		v = constant.Real(v)
 	}
 
@@ -321,25 +308,6 @@ func toint(v constant.Value) constant.Value {
 	return constant.MakeInt64(1)
 }
 
-// overflow reports whether constant value v is too large
-// to represent with type t, and emits an error message if so.
-func overflow(v constant.Value, t *types.Type) bool {
-	// v has already been converted
-	// to appropriate form for t.
-	if t.IsUntyped() {
-		return false
-	}
-	if v.Kind() == constant.Int && constant.BitLen(v) > ir.ConstPrec {
-		base.Errorf("integer too large")
-		return true
-	}
-	if ir.ConstOverflow(v, t) {
-		base.Errorf("constant %v overflows %v", types.FmtConst(v, false), t)
-		return true
-	}
-	return false
-}
-
 func tostr(v constant.Value) constant.Value {
 	if v.Kind() == constant.Int {
 		r := unicode.ReplacementChar
diff --git a/test/fixedbugs/issue58293.go b/test/fixedbugs/issue58293.go
new file mode 100644
index 0000000000..58d5500253
--- /dev/null
+++ b/test/fixedbugs/issue58293.go
@@ -0,0 +1,13 @@
+// compile
+
+// Copyright 2023 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.
+
+package p
+
+var bar = f(13579)
+
+func f(x uint16) uint16 {
+	return x>>8 | x<<8
+}