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fix before precedence relation

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"before" precedence relation should be transitive, such that if a is
before b, and b is before c, then a should before c
This commit is contained in:
Yi Yang 2024-07-01 15:47:37 +08:00
parent 9fd9a54977
commit 36f564c189
1 changed files with 34 additions and 5 deletions
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35
src/cmd/compile/internal/ssa/layout.go
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@ -291,12 +291,36 @@ func (g *chainGraph) print() {
fmt.Printf("%v\n", blockOrder)
}
func greedyBlockOrder(fn *Func) []*Block {
func newChainGraph(fn *Func) *chainGraph {
graph := &chainGraph{
chains: []*chain{},
edges: []*edge{},
b2chain: make([]*chain, fn.NumBlocks(), fn.NumBlocks()),
}
return graph
}
// isBefore returns true if block a is before block b in the block order. The
// "before" precedence relation is transitive, i.e., if a is before b and b is
// before c, then a is before c.
func isBefore(before map[*chain][]*chain, visited map[*chain]bool, a, b *chain) bool {
if _, ok := visited[a]; ok {
return false
}
visited[a] = true
for _, c := range before[a] {
if c == b {
return true
}
if isBefore(before, visited, c, b) {
return true
}
}
return false
}
func greedyBlockOrder(fn *Func) []*Block {
graph := newChainGraph(fn)
// Initially every block is in its own chain
for _, block := range fn.Blocks {
@ -377,6 +401,9 @@ func greedyBlockOrder(fn *Func) []*Block {
src := graph.getChain(edge.src)
dst := graph.getChain(edge.dst)
before[src] = append(before[src], dst)
if fn.pass.debug > 2 {
fmt.Printf("%v comes before %v\n", src.blocks, dst.blocks)
}
}
}
sort.SliceStable(graph.chains, func(i, j int) bool {
@ -389,10 +416,12 @@ func greedyBlockOrder(fn *Func) []*Block {
return false
}
// Respect precedence relation
for _, b := range before[c1] {
if b == c2 {
visited := make(map[*chain]bool)
if isBefore(before, visited, c1, c2) {
return true
}
if isBefore(before, visited, c2, c1) {
return false
}
// Higher merge count is considered
if c1.priority != c2.priority {