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cmd/asm: fix encoding for arm right shift by constant 0

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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>
This commit is contained in:
Keith Randall 2023-12-14 13:07:50 -08:00
parent 5e939b3a9c
commit b60bf8f8e1
4 changed files with 42 additions and 0 deletions
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8
src/cmd/asm/internal/asm/testdata/arm.s vendored
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@ -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

8
src/cmd/internal/obj/arm/asm5.go
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@ -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]

25
test/fixedbugs/issue64715.go Normal file
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@ -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)))
}

1
test/fixedbugs/issue64715.out Normal file
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@ -0,0 +1 @@
65535