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cmd/compile: enhance the chunked indexing case to include reslicing

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this helps SIMD, but also helps plain old Go

Cherry-picked from the dev.simd branch. This CL is not
necessarily SIMD specific. Apply early to reduce risk.

Change-Id: Idcdacd54b6776f5c32b497bc94485052611cfa8d
Reviewed-on: https://go-review.googlesource.com/c/go/+/704756
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/708862
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
David Chase 2025-09-17 14:25:16 -04:00 • committed by Cherry Mui
parent ad3db2562e
commit 20c9377e47
1 changed files with 26 additions and 8 deletions
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32
src/cmd/compile/internal/ssa/prove.go
View file

@ -2177,10 +2177,18 @@ func unsignedSubUnderflows(a, b uint64) bool {
// checkForChunkedIndexBounds looks for index expressions of the form // checkForChunkedIndexBounds looks for index expressions of the form
// A[i+delta] where delta < K and i <= len(A)-K. That is, this is a chunked // A[i+delta] where delta < K and i <= len(A)-K. That is, this is a chunked
// iteration where the index is not directly compared to the length. // iteration where the index is not directly compared to the length.
func checkForChunkedIndexBounds(ft *factsTable, b *Block, index, bound *Value) bool { // if isReslice, then delta can be equal to K.
if bound.Op != OpSliceLen { func checkForChunkedIndexBounds(ft *factsTable, b *Block, index, bound *Value, isReslice bool) bool {
if bound.Op != OpSliceLen && bound.Op != OpSliceCap {
return false return false
} }
// this is a slice bounds check against len or capacity,
// and refers back to a prior check against length, which
// will also work for the cap since that is not smaller
// than the length.
slice := bound.Args[0]
lim := ft.limits[index.ID] lim := ft.limits[index.ID]
if lim.min < 0 { if lim.min < 0 {
return false return false
@ -2206,9 +2214,9 @@ func checkForChunkedIndexBounds(ft *factsTable, b *Block, index, bound *Value) b
} }
if ow := o.w; ow.Op == OpAdd64 { if ow := o.w; ow.Op == OpAdd64 {
var lenOffset *Value var lenOffset *Value
if ow.Args[0] == bound { if bound := ow.Args[0]; bound.Op == OpSliceLen && bound.Args[0] == slice {
lenOffset = ow.Args[1] lenOffset = ow.Args[1]
} else if ow.Args[1] == bound { } else if bound := ow.Args[1]; bound.Op == OpSliceLen && bound.Args[0] == slice {
lenOffset = ow.Args[0] lenOffset = ow.Args[0]
} }
if lenOffset == nil || lenOffset.Op != OpConst64 { if lenOffset == nil || lenOffset.Op != OpConst64 {
@ -2216,12 +2224,15 @@ func checkForChunkedIndexBounds(ft *factsTable, b *Block, index, bound *Value) b
} }
if K := -lenOffset.AuxInt; K >= 0 { if K := -lenOffset.AuxInt; K >= 0 {
or := o.r or := o.r
if isReslice {
K++
}
if or == lt { if or == lt {
or = lt | eq or = lt | eq
K++ K++
if K < 0 {
continue
} }
if K < 0 { // We hate thinking about overflow
continue
} }
if delta < K && or == lt|eq { if delta < K && or == lt|eq {
@ -2345,12 +2356,19 @@ func addLocalFacts(ft *factsTable, b *Block) {
ft.update(b, v, v.Args[0].Args[2], signed, eq) ft.update(b, v, v.Args[0].Args[2], signed, eq)
} }
case OpIsInBounds: case OpIsInBounds:
if checkForChunkedIndexBounds(ft, b, v.Args[0], v.Args[1]) { if checkForChunkedIndexBounds(ft, b, v.Args[0], v.Args[1], false) {
if b.Func.pass.debug > 0 { if b.Func.pass.debug > 0 {
b.Func.Warnl(v.Pos, "Proved %s for blocked indexing", v.Op) b.Func.Warnl(v.Pos, "Proved %s for blocked indexing", v.Op)
} }
ft.booleanTrue(v) ft.booleanTrue(v)
} }
case OpIsSliceInBounds:
if checkForChunkedIndexBounds(ft, b, v.Args[0], v.Args[1], true) {
if b.Func.pass.debug > 0 {
b.Func.Warnl(v.Pos, "Proved %s for blocked reslicing", v.Op)
}
ft.booleanTrue(v)
}
case OpPhi: case OpPhi:
addLocalFactsPhi(ft, v) addLocalFactsPhi(ft, v)
} }