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cmd/compile: don't short-circuit copies whose source is volatile

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Current optimization: When we copy a->b and then b->c, we might as well
copy a->c instead of b->c (then b might be dead and go away).

*Except* if a is a volatile location (might be clobbered by a call).
In that case, we really do want to copy a immediately, because there
might be a call before we can do the a->c copy.

User calls can't happen in between, because the rule matches up the
memory states. But calls inserted for memory barriers, particularly
runtime.typedmemmove, can.

(I guess we could introduce a register-calling-convention version
of runtime.typedmemmove, but that seems a bigger change than this one.)

Fixes #43570

Change-Id: Ifa518bb1a6f3a8dd46c352d4fd54ea9713b3eb1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/282492
Trust: Keith Randall <khr@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
This commit is contained in:
Keith Randall 2021-01-07 14:57:53 -08:00
parent ae97717133
commit 304f769ffc
3 changed files with 46 additions and 6 deletions
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4
src/cmd/compile/internal/ssa/gen/generic.rules
View File

@ -2512,7 +2512,7 @@
(Move {t1} [s] dst tmp1 midmem:(Move {t2} [s] tmp2 src _))
&& t1.Compare(t2) == types.CMPeq
&& isSamePtr(tmp1, tmp2)
&& isStackPtr(src)
&& isStackPtr(src) && !isVolatile(src)
&& disjoint(src, s, tmp2, s)
&& (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
=> (Move {t1} [s] dst src midmem)
@ -2521,7 +2521,7 @@
(Move {t1} [s] dst tmp1 midmem:(VarDef (Move {t2} [s] tmp2 src _)))
&& t1.Compare(t2) == types.CMPeq
&& isSamePtr(tmp1, tmp2)
&& isStackPtr(src)
&& isStackPtr(src) && !isVolatile(src)
&& disjoint(src, s, tmp2, s)
&& (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
=> (Move {t1} [s] dst src midmem)

8
src/cmd/compile/internal/ssa/rewritegeneric.go
View File

@ -13637,7 +13637,7 @@ func rewriteValuegeneric_OpMove(v *Value) bool {
return true
}
// match: (Move {t1} [s] dst tmp1 midmem:(Move {t2} [s] tmp2 src _))
// cond: t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
// cond: t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
// result: (Move {t1} [s] dst src midmem)
for {
s := auxIntToInt64(v.AuxInt)
@ -13651,7 +13651,7 @@ func rewriteValuegeneric_OpMove(v *Value) bool {
t2 := auxToType(midmem.Aux)
src := midmem.Args[1]
tmp2 := midmem.Args[0]
if !(t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
if !(t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
break
}
v.reset(OpMove)
@ -13661,7 +13661,7 @@ func rewriteValuegeneric_OpMove(v *Value) bool {
return true
}
// match: (Move {t1} [s] dst tmp1 midmem:(VarDef (Move {t2} [s] tmp2 src _)))
// cond: t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
// cond: t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
// result: (Move {t1} [s] dst src midmem)
for {
s := auxIntToInt64(v.AuxInt)
@ -13679,7 +13679,7 @@ func rewriteValuegeneric_OpMove(v *Value) bool {
t2 := auxToType(midmem_0.Aux)
src := midmem_0.Args[1]
tmp2 := midmem_0.Args[0]
if !(t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
if !(t1.Compare(t2) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
break
}
v.reset(OpMove)

40
test/fixedbugs/issue43570.go Normal file
View File

@ -0,0 +1,40 @@
// run
// Copyright 2021 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
import "fmt"
type T [8]*int
//go:noinline
func f(x int) T {
return T{}
}
//go:noinline
func g(x int, t T) {
if t != (T{}) {
panic(fmt.Sprintf("bad: %v", t))
}
}
func main() {
const N = 10000
var q T
func() {
for i := 0; i < N; i++ {
q = f(0)
g(0, q)
sink = make([]byte, 1024)
}
}()
// Note that the closure is a trick to get the write to q to be a
// write to a pointer that is known to be non-nil and requires
// a write barrier.
}
var sink []byte