cmd/compile: tweak offset-generator to elide more +0 offsets
this caused a problem in write barrier code when a spurious
zero-offset prevented a write barrier elision.
removed cache after instrumenting it and discovering
zero safe hits (one value must dominate the other, else
unsafe).
Change-Id: I42dfdb4d38ebfe158b13e766a7fabfc514d773f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/297349
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
diff --git a/src/cmd/compile/internal/ssa/expand_calls.go b/src/cmd/compile/internal/ssa/expand_calls.go
index fd8ae30..03b2a98 100644
--- a/src/cmd/compile/internal/ssa/expand_calls.go
+++ b/src/cmd/compile/internal/ssa/expand_calls.go
@@ -20,12 +20,6 @@
typ *types.Type
}
-type offsetKey struct {
- from *Value
- offset int64
- pt *types.Type
-}
-
type Abi1RO uint8 // An offset within a parameter's slice of register indices, for abi1.
func isBlockMultiValueExit(b *Block) bool {
@@ -194,8 +188,7 @@
sdom SparseTree
commonSelectors map[selKey]*Value // used to de-dupe selectors
commonArgs map[selKey]*Value // used to de-dupe OpArg/OpArgIntReg/OpArgFloatReg
- offsets map[offsetKey]*Value
- memForCall map[ID]*Value // For a call, need to know the unique selector that gets the mem.
+ memForCall map[ID]*Value // For a call, need to know the unique selector that gets the mem.
}
// intPairTypes returns the pair of 32-bit int types needed to encode a 64-bit integer type on a target
@@ -223,9 +216,16 @@
// offsetFrom creates an offset from a pointer, simplifying chained offsets and offsets from SP
// TODO should also optimize offsets from SB?
-func (x *expandState) offsetFrom(from *Value, offset int64, pt *types.Type) *Value {
- if offset == 0 && from.Type == pt { // this is not actually likely
- return from
+func (x *expandState) offsetFrom(b *Block, from *Value, offset int64, pt *types.Type) *Value {
+ ft := from.Type
+ if offset == 0 {
+ if ft == pt {
+ return from
+ }
+ // This captures common, (apparently) safe cases. The unsafe cases involve ft == uintptr
+ if (ft.IsPtr() || ft.IsUnsafePtr()) && pt.IsPtr() {
+ return from
+ }
}
// Simplify, canonicalize
for from.Op == OpOffPtr {
@@ -235,14 +235,7 @@
if from == x.sp {
return x.f.ConstOffPtrSP(pt, offset, x.sp)
}
- key := offsetKey{from, offset, pt}
- v := x.offsets[key]
- if v != nil {
- return v
- }
- v = from.Block.NewValue1I(from.Pos.WithNotStmt(), OpOffPtr, pt, offset, from)
- x.offsets[key] = v
- return v
+ return b.NewValue1I(from.Pos.WithNotStmt(), OpOffPtr, pt, offset, from)
}
// splitSlots splits one "field" (specified by sfx, offset, and ty) out of the LocalSlots in ls and returns the new LocalSlots this generates.
@@ -426,7 +419,7 @@
leaf.copyOf(w)
}
} else {
- off := x.offsetFrom(x.sp, offset+aux.OffsetOfResult(which), pt)
+ off := x.offsetFrom(x.f.Entry, x.sp, offset+aux.OffsetOfResult(which), pt)
if leaf.Block == call.Block {
leaf.reset(OpLoad)
leaf.SetArgs2(off, call)
@@ -531,7 +524,7 @@
func (x *expandState) rewriteDereference(b *Block, base, a, mem *Value, offset, size int64, typ *types.Type, pos src.XPos) *Value {
source := a.Args[0]
- dst := x.offsetFrom(base, offset, source.Type)
+ dst := x.offsetFrom(b, base, offset, source.Type)
if a.Uses == 1 && a.Block == b {
a.reset(OpMove)
a.Pos = pos
@@ -624,7 +617,7 @@
// storeOneLoad creates a decomposed (one step) load that is then stored.
func storeOneLoad(x *expandState, pos src.XPos, b *Block, source, mem *Value, t *types.Type, offArg, offStore int64, loadRegOffset Abi1RO, storeRc registerCursor) *Value {
- from := x.offsetFrom(source.Args[0], offArg, types.NewPtr(t))
+ from := x.offsetFrom(b, source.Args[0], offArg, types.NewPtr(t))
w := source.Block.NewValue2(source.Pos, OpLoad, t, from, mem)
return x.storeArgOrLoad(pos, b, w, mem, t, offStore, loadRegOffset, storeRc)
}
@@ -826,7 +819,7 @@
if storeRc.hasRegs() {
storeRc.addArg(source)
} else {
- dst := x.offsetFrom(storeRc.storeDest, offset, types.NewPtr(t))
+ dst := x.offsetFrom(b, storeRc.storeDest, offset, types.NewPtr(t))
s = b.NewValue3A(pos, OpStore, types.TypeMem, t, dst, source, mem)
}
if x.debug {
@@ -904,7 +897,6 @@
namedSelects: make(map[*Value][]namedVal),
sdom: f.Sdom(),
commonArgs: make(map[selKey]*Value),
- offsets: make(map[offsetKey]*Value),
memForCall: make(map[ID]*Value),
}
@@ -1098,7 +1090,7 @@
which := v.AuxInt
aux := call.Aux.(*AuxCall)
pt := v.Type
- off := x.offsetFrom(x.sp, aux.OffsetOfResult(which), pt)
+ off := x.offsetFrom(x.f.Entry, x.sp, aux.OffsetOfResult(which), pt)
v.copyOf(off)
}
}
