cmd/gc: error on constant shift overflows.
Fixes #3019.
R=golang-dev, rsc
CC=golang-dev, remy
https://golang.org/cl/5674044
diff --git a/test/const2.go b/test/const2.go
index b083735..12c5c24 100644
--- a/test/const2.go
+++ b/test/const2.go
@@ -13,4 +13,6 @@
const LargeA = 1000000000000000000
const LargeB = LargeA * LargeA * LargeA
-const LargeC = LargeB * LargeB * LargeB // ERROR "constant multiplication overflow"
+const LargeC = LargeB * LargeB * LargeB // ERROR "constant multiplication overflow"
+
+const AlsoLargeA = LargeA << 400 << 400 >> 400 >> 400 // ERROR "constant shift overflow"
