[dev.ssa] cmd/compile: rewrites for constant shifts
Add rewrite rules to optimize constant shifts.
Fixes #10637
Change-Id: I74b724d3e81aeb7098c696d02c050f7fdfd5b523
Reviewed-on: https://go-review.googlesource.com/19106
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index f7da347..7dd0d2e 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -181,6 +181,11 @@
return int64(math.Float64bits(f))
}
+// uaddOvf returns true if unsigned a+b would overflow.
+func uaddOvf(a, b int64) bool {
+ return uint64(a)+uint64(b) < uint64(a)
+}
+
// DUFFZERO consists of repeated blocks of 4 MOVUPSs + ADD,
// See runtime/mkduff.go.
const (
