cmd/asm: fix encoding for arm right shift by constant 0
Right shifts, for some odd reasons, can encode shifts of constant
1-32 instead of 0-31. Left shifts, however, can encode shifts 0-31.
When the shift amount is 0, arm recommends encoding right shifts
using left shifts.
Fixes #64715
Change-Id: Id3825349aa7195028037893dfe01fa0e405eaa51
Reviewed-on: https://go-review.googlesource.com/c/go/+/549955
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
diff --git a/src/cmd/asm/internal/asm/testdata/arm.s b/src/cmd/asm/internal/asm/testdata/arm.s
index 2ba22c7..2b8cadb 100644
--- a/src/cmd/asm/internal/asm/testdata/arm.s
+++ b/src/cmd/asm/internal/asm/testdata/arm.s
@@ -870,10 +870,13 @@
BIC.S R0@>R1, R2 // 7021d2e1
// SRL
+ SRL $0, R5, R6 // 0560a0e1
+ SRL $1, R5, R6 // a560a0e1
SRL $14, R5, R6 // 2567a0e1
SRL $15, R5, R6 // a567a0e1
SRL $30, R5, R6 // 256fa0e1
SRL $31, R5, R6 // a56fa0e1
+ SRL $32, R5, R6 // 2560a0e1
SRL.S $14, R5, R6 // 2567b0e1
SRL.S $15, R5, R6 // a567b0e1
SRL.S $30, R5, R6 // 256fb0e1
@@ -892,10 +895,13 @@
SRL.S R5, R7 // 3775b0e1
// SRA
+ SRA $0, R5, R6 // 0560a0e1
+ SRA $1, R5, R6 // c560a0e1
SRA $14, R5, R6 // 4567a0e1
SRA $15, R5, R6 // c567a0e1
SRA $30, R5, R6 // 456fa0e1
SRA $31, R5, R6 // c56fa0e1
+ SRA $32, R5, R6 // 4560a0e1
SRA.S $14, R5, R6 // 4567b0e1
SRA.S $15, R5, R6 // c567b0e1
SRA.S $30, R5, R6 // 456fb0e1
@@ -914,6 +920,8 @@
SRA.S R5, R7 // 5775b0e1
// SLL
+ SLL $0, R5, R6 // 0560a0e1
+ SLL $1, R5, R6 // 8560a0e1
SLL $14, R5, R6 // 0567a0e1
SLL $15, R5, R6 // 8567a0e1
SLL $30, R5, R6 // 056fa0e1
diff --git a/src/cmd/internal/obj/arm/asm5.go b/src/cmd/internal/obj/arm/asm5.go
index 24b9bdd..9731bd4 100644
--- a/src/cmd/internal/obj/arm/asm5.go
+++ b/src/cmd/internal/obj/arm/asm5.go
@@ -1099,6 +1099,14 @@
fmt.Printf("\t\t%d %d\n", p.From.Type, p.To.Type)
}
+ if (p.As == ASRL || p.As == ASRA) && p.From.Type == obj.TYPE_CONST && p.From.Offset == 0 {
+ // Right shifts are weird - a shift that looks like "shift by constant 0" actually
+ // means "shift by constant 32". Use left shift in this situation instead.
+ // See issue 64715.
+ // TODO: rotate by 0? Not currently supported, but if we ever do then include it here.
+ p.As = ASLL
+ }
+
ops := oprange[p.As&obj.AMask]
c1 := &xcmp[a1]
c3 := &xcmp[a3]
diff --git a/test/fixedbugs/issue64715.go b/test/fixedbugs/issue64715.go
new file mode 100644
index 0000000..bf11716
--- /dev/null
+++ b/test/fixedbugs/issue64715.go
@@ -0,0 +1,25 @@
+// run
+
+// 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 main
+
+func boolInt32(b bool) int32 {
+ if b {
+ return 1
+ }
+
+ return 0
+}
+
+func f(left uint16, right int32) (r uint16) {
+ return left >> right
+}
+
+var n = uint16(65535)
+
+func main() {
+ println(f(n, boolInt32(int64(n^n) > 1)))
+}
diff --git a/test/fixedbugs/issue64715.out b/test/fixedbugs/issue64715.out
new file mode 100644
index 0000000..7a53b35
--- /dev/null
+++ b/test/fixedbugs/issue64715.out
@@ -0,0 +1 @@
+65535
