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 2ba22c71dec17f2c09e5a754ec216ca969184ab0..2b8cadbed8bbea770349ec99248c1e022fb45411 100644 (file)
--- a/src/cmd/asm/internal/asm/testdata/arm.s
+++ b/src/cmd/asm/internal/asm/testdata/arm.s
@@ -870,10 +870,13 @@ jmp_label_3:
        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 @@ jmp_label_3:
        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 @@ jmp_label_3:
        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 24b9bdd980c8bb2325f4d98fc82ddfde3449de86..9731bd415140372ac8e1c2247c7eac883b3d974c 100644 (file)
--- a/src/cmd/internal/obj/arm/asm5.go
+++ b/src/cmd/internal/obj/arm/asm5.go
@@ -1099,6 +1099,14 @@ func (c *ctxt5) oplook(p *obj.Prog) *Optab {
                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 (file)
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 (file)
index 0000000..7a53b35
--- /dev/null
+++ b/test/fixedbugs/issue64715.out
@@ -0,0 +1 @@
+65535