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cmd/compile/internal/ssa: recognize constant pointer comparison

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Teach the backend to recognize that the address of a symbol
is equal with itself, and that the addresses of two different
symbols are different.

Some examples of where this rule hits in the standard library:

 - inlined uses of (*time.Time).setLoc (e.g. time.UTC)
 - inlined uses of bufio.NewReader (via type assertion)

Change-Id: I23dcb068c2ec333655c1292917bec13bbd908c24
Reviewed-on: https://go-review.googlesource.com/38338
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
philhofer 2017-03-15 15:34:52 -07:00 committed by Josh Bleecher Snyder
parent f8b0231639
commit d68bb16b1e
3 changed files with 43 additions and 3 deletions
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8
src/cmd/compile/internal/gc/ssa.go
View File

@ -1366,7 +1366,7 @@ func (s *state) expr(n *Node) *ssa.Value {
if n.Class == PFUNC {
// "value" of a function is the address of the function's closure
sym := Linksym(funcsym(n.Sym))
aux := &ssa.ExternSymbol{Typ: n.Type, Sym: sym}
aux := s.lookupSymbol(n, &ssa.ExternSymbol{Typ: n.Type, Sym: sym})
return s.entryNewValue1A(ssa.OpAddr, typPtr(n.Type), aux, s.sb)
}
if s.canSSA(n) {
@ -2137,7 +2137,8 @@ func (s *state) append(n *Node, inplace bool) *ssa.Value {
// Call growslice
s.startBlock(grow)
taddr := s.newValue1A(ssa.OpAddr, Types[TUINTPTR], &ssa.ExternSymbol{Typ: Types[TUINTPTR], Sym: Linksym(typenamesym(n.Type.Elem()))}, s.sb)
sym := s.lookupSymbol(n, &ssa.ExternSymbol{Typ: Types[TUINTPTR], Sym: Linksym(typenamesym(n.Type.Elem()))})
taddr := s.newValue1A(ssa.OpAddr, Types[TUINTPTR], sym, s.sb)
r := s.rtcall(growslice, true, []*Type{pt, Types[TINT], Types[TINT]}, taddr, p, l, c, nl)
@ -4087,7 +4088,8 @@ func (s *state) dottype(n *Node, commaok bool) (res, resok *ssa.Value) {
if !commaok {
// on failure, panic by calling panicdottype
s.startBlock(bFail)
taddr := s.newValue1A(ssa.OpAddr, byteptr, &ssa.ExternSymbol{Typ: byteptr, Sym: Linksym(typenamesym(n.Left.Type))}, s.sb)
sym := s.lookupSymbol(n, &ssa.ExternSymbol{Typ: byteptr, Sym: Linksym(typenamesym(n.Left.Type))})
taddr := s.newValue1A(ssa.OpAddr, byteptr, sym, s.sb)
if n.Left.Type.IsEmptyInterface() {
s.rtcall(panicdottypeE, false, nil, itab, target, taddr)
} else {

4
src/cmd/compile/internal/ssa/gen/generic.rules
View File

@ -1432,6 +1432,10 @@
&& warnRule(fe.Debug_checknil() && v.Pos.Line() > 1, v, "removed nil check")
-> (Invalid)
// Address comparison shows up in type assertions.
(EqPtr x x) -> (ConstBool [1])
(EqPtr (Addr {a} x) (Addr {b} x)) -> (ConstBool [b2i(a == b)])
// De-virtualize interface calls into static calls.
// Note that (ITab (IMake)) doesn't get
// rewritten until after the first opt pass,

34
src/cmd/compile/internal/ssa/rewritegeneric.go
View File

@ -5332,6 +5332,40 @@ func rewriteValuegeneric_OpEqPtr(v *Value) bool {
v.AddArg(v0)
return true
}
// match: (EqPtr x x)
// cond:
// result: (ConstBool [1])
for {
x := v.Args[0]
if x != v.Args[1] {
break
}
v.reset(OpConstBool)
v.AuxInt = 1
return true
}
// match: (EqPtr (Addr {a} x) (Addr {b} x))
// cond:
// result: (ConstBool [b2i(a == b)])
for {
v_0 := v.Args[0]
if v_0.Op != OpAddr {
break
}
a := v_0.Aux
x := v_0.Args[0]
v_1 := v.Args[1]
if v_1.Op != OpAddr {
break
}
b := v_1.Aux
if x != v_1.Args[0] {
break
}
v.reset(OpConstBool)
v.AuxInt = b2i(a == b)
return true
}
return false
}
func rewriteValuegeneric_OpEqSlice(v *Value) bool {