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[release-branch.go1.21] Revert "cmd/compile: don't combine loads in generated equality functions" 

This reverts CL 583303.

Reason for revert: release branch is currently frozen.

Change-Id: Icbdb73b5b40690a875497dd0dc57ca84c728ef6f
Reviewed-on: https://go-review.googlesource.com/c/go/+/582961
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
This commit is contained in:
Cherry Mui 2024-05-06 20:18:00 +00:00
parent 58e77ad9b9
commit 78d89b2b67
2 changed files with 1 additions and 38 deletions
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7
src/cmd/compile/internal/compare/compare.go
View File

@ -148,7 +148,7 @@ func calculateCostForType(t *types.Type) int64 {
return EqStructCost(t)
case types.TSLICE:
// Slices are not comparable.
base.Fatalf("calculateCostForType: unexpected slice type")
base.Fatalf("eqStructFieldCost: unexpected slice type")
case types.TARRAY:
elemCost := calculateCostForType(t.Elem())
cost = t.NumElem() * elemCost
@ -374,11 +374,6 @@ func eqmem(p ir.Node, q ir.Node, field *types.Sym, size int64) ir.Node {
}
func eqmemfunc(size int64, t *types.Type) (fn *ir.Name, needsize bool) {
if !base.Ctxt.Arch.CanMergeLoads && t.Alignment() < int64(base.Ctxt.Arch.Alignment) && t.Alignment() < t.Size() {
// We can't use larger comparisons if the value might not be aligned
// enough for the larger comparison. See issues 46283 and 67160.
size = 0
}
switch size {
default:
fn = typecheck.LookupRuntime("memequal")

32
test/fixedbugs/issue67160.go
View File

@ -1,32 +0,0 @@
// run
// Copyright 2024 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.
// Test to make sure that we don't try using larger loads for
// generated equality functions on architectures that can't do
// unaligned loads.
package main
// T has a big field that wants to be compared with larger loads/stores.
// T is "special" because of the unnamed field, so it needs a generated equality function.
// T is an odd number of bytes in size and has alignment 1.
type T struct {
src [8]byte
_ byte
}
// U contains 8 copies of T, each at a different %8 alignment.
type U [8]T
//go:noinline
func f(x, y *U) bool {
return *x == *y
}
func main() {
var a U
_ = f(&a, &a)
}