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Diffstat (limited to 'vendor/golang.org/x/tools/go/ssa/dom.go')
| -rw-r--r-- | vendor/golang.org/x/tools/go/ssa/dom.go | 341 |
1 files changed, 0 insertions, 341 deletions
diff --git a/vendor/golang.org/x/tools/go/ssa/dom.go b/vendor/golang.org/x/tools/go/ssa/dom.go deleted file mode 100644 index 12ef430..0000000 --- a/vendor/golang.org/x/tools/go/ssa/dom.go +++ /dev/null @@ -1,341 +0,0 @@ -// Copyright 2013 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 ssa - -// This file defines algorithms related to dominance. - -// Dominator tree construction ---------------------------------------- -// -// We use the algorithm described in Lengauer & Tarjan. 1979. A fast -// algorithm for finding dominators in a flowgraph. -// http://doi.acm.org/10.1145/357062.357071 -// -// We also apply the optimizations to SLT described in Georgiadis et -// al, Finding Dominators in Practice, JGAA 2006, -// http://jgaa.info/accepted/2006/GeorgiadisTarjanWerneck2006.10.1.pdf -// to avoid the need for buckets of size > 1. - -import ( - "bytes" - "fmt" - "math/big" - "os" - "sort" -) - -// Idom returns the block that immediately dominates b: -// its parent in the dominator tree, if any. -// Neither the entry node (b.Index==0) nor recover node -// (b==b.Parent().Recover()) have a parent. -// -func (b *BasicBlock) Idom() *BasicBlock { return b.dom.idom } - -// Dominees returns the list of blocks that b immediately dominates: -// its children in the dominator tree. -// -func (b *BasicBlock) Dominees() []*BasicBlock { return b.dom.children } - -// Dominates reports whether b dominates c. -func (b *BasicBlock) Dominates(c *BasicBlock) bool { - return b.dom.pre <= c.dom.pre && c.dom.post <= b.dom.post -} - -type byDomPreorder []*BasicBlock - -func (a byDomPreorder) Len() int { return len(a) } -func (a byDomPreorder) Swap(i, j int) { a[i], a[j] = a[j], a[i] } -func (a byDomPreorder) Less(i, j int) bool { return a[i].dom.pre < a[j].dom.pre } - -// DomPreorder returns a new slice containing the blocks of f in -// dominator tree preorder. -// -func (f *Function) DomPreorder() []*BasicBlock { - n := len(f.Blocks) - order := make(byDomPreorder, n, n) - copy(order, f.Blocks) - sort.Sort(order) - return order -} - -// domInfo contains a BasicBlock's dominance information. -type domInfo struct { - idom *BasicBlock // immediate dominator (parent in domtree) - children []*BasicBlock // nodes immediately dominated by this one - pre, post int32 // pre- and post-order numbering within domtree -} - -// ltState holds the working state for Lengauer-Tarjan algorithm -// (during which domInfo.pre is repurposed for CFG DFS preorder number). -type ltState struct { - // Each slice is indexed by b.Index. - sdom []*BasicBlock // b's semidominator - parent []*BasicBlock // b's parent in DFS traversal of CFG - ancestor []*BasicBlock // b's ancestor with least sdom -} - -// dfs implements the depth-first search part of the LT algorithm. -func (lt *ltState) dfs(v *BasicBlock, i int32, preorder []*BasicBlock) int32 { - preorder[i] = v - v.dom.pre = i // For now: DFS preorder of spanning tree of CFG - i++ - lt.sdom[v.Index] = v - lt.link(nil, v) - for _, w := range v.Succs { - if lt.sdom[w.Index] == nil { - lt.parent[w.Index] = v - i = lt.dfs(w, i, preorder) - } - } - return i -} - -// eval implements the EVAL part of the LT algorithm. -func (lt *ltState) eval(v *BasicBlock) *BasicBlock { - // TODO(adonovan): opt: do path compression per simple LT. - u := v - for ; lt.ancestor[v.Index] != nil; v = lt.ancestor[v.Index] { - if lt.sdom[v.Index].dom.pre < lt.sdom[u.Index].dom.pre { - u = v - } - } - return u -} - -// link implements the LINK part of the LT algorithm. -func (lt *ltState) link(v, w *BasicBlock) { - lt.ancestor[w.Index] = v -} - -// buildDomTree computes the dominator tree of f using the LT algorithm. -// Precondition: all blocks are reachable (e.g. optimizeBlocks has been run). -// -func buildDomTree(f *Function) { - // The step numbers refer to the original LT paper; the - // reordering is due to Georgiadis. - - // Clear any previous domInfo. - for _, b := range f.Blocks { - b.dom = domInfo{} - } - - n := len(f.Blocks) - // Allocate space for 5 contiguous [n]*BasicBlock arrays: - // sdom, parent, ancestor, preorder, buckets. - space := make([]*BasicBlock, 5*n, 5*n) - lt := ltState{ - sdom: space[0:n], - parent: space[n : 2*n], - ancestor: space[2*n : 3*n], - } - - // Step 1. Number vertices by depth-first preorder. - preorder := space[3*n : 4*n] - root := f.Blocks[0] - prenum := lt.dfs(root, 0, preorder) - recover := f.Recover - if recover != nil { - lt.dfs(recover, prenum, preorder) - } - - buckets := space[4*n : 5*n] - copy(buckets, preorder) - - // In reverse preorder... - for i := int32(n) - 1; i > 0; i-- { - w := preorder[i] - - // Step 3. Implicitly define the immediate dominator of each node. - for v := buckets[i]; v != w; v = buckets[v.dom.pre] { - u := lt.eval(v) - if lt.sdom[u.Index].dom.pre < i { - v.dom.idom = u - } else { - v.dom.idom = w - } - } - - // Step 2. Compute the semidominators of all nodes. - lt.sdom[w.Index] = lt.parent[w.Index] - for _, v := range w.Preds { - u := lt.eval(v) - if lt.sdom[u.Index].dom.pre < lt.sdom[w.Index].dom.pre { - lt.sdom[w.Index] = lt.sdom[u.Index] - } - } - - lt.link(lt.parent[w.Index], w) - - if lt.parent[w.Index] == lt.sdom[w.Index] { - w.dom.idom = lt.parent[w.Index] - } else { - buckets[i] = buckets[lt.sdom[w.Index].dom.pre] - buckets[lt.sdom[w.Index].dom.pre] = w - } - } - - // The final 'Step 3' is now outside the loop. - for v := buckets[0]; v != root; v = buckets[v.dom.pre] { - v.dom.idom = root - } - - // Step 4. Explicitly define the immediate dominator of each - // node, in preorder. - for _, w := range preorder[1:] { - if w == root || w == recover { - w.dom.idom = nil - } else { - if w.dom.idom != lt.sdom[w.Index] { - w.dom.idom = w.dom.idom.dom.idom - } - // Calculate Children relation as inverse of Idom. - w.dom.idom.dom.children = append(w.dom.idom.dom.children, w) - } - } - - pre, post := numberDomTree(root, 0, 0) - if recover != nil { - numberDomTree(recover, pre, post) - } - - // printDomTreeDot(os.Stderr, f) // debugging - // printDomTreeText(os.Stderr, root, 0) // debugging - - if f.Prog.mode&SanityCheckFunctions != 0 { - sanityCheckDomTree(f) - } -} - -// numberDomTree sets the pre- and post-order numbers of a depth-first -// traversal of the dominator tree rooted at v. These are used to -// answer dominance queries in constant time. -// -func numberDomTree(v *BasicBlock, pre, post int32) (int32, int32) { - v.dom.pre = pre - pre++ - for _, child := range v.dom.children { - pre, post = numberDomTree(child, pre, post) - } - v.dom.post = post - post++ - return pre, post -} - -// Testing utilities ---------------------------------------- - -// sanityCheckDomTree checks the correctness of the dominator tree -// computed by the LT algorithm by comparing against the dominance -// relation computed by a naive Kildall-style forward dataflow -// analysis (Algorithm 10.16 from the "Dragon" book). -// -func sanityCheckDomTree(f *Function) { - n := len(f.Blocks) - - // D[i] is the set of blocks that dominate f.Blocks[i], - // represented as a bit-set of block indices. - D := make([]big.Int, n) - - one := big.NewInt(1) - - // all is the set of all blocks; constant. - var all big.Int - all.Set(one).Lsh(&all, uint(n)).Sub(&all, one) - - // Initialization. - for i, b := range f.Blocks { - if i == 0 || b == f.Recover { - // A root is dominated only by itself. - D[i].SetBit(&D[0], 0, 1) - } else { - // All other blocks are (initially) dominated - // by every block. - D[i].Set(&all) - } - } - - // Iteration until fixed point. - for changed := true; changed; { - changed = false - for i, b := range f.Blocks { - if i == 0 || b == f.Recover { - continue - } - // Compute intersection across predecessors. - var x big.Int - x.Set(&all) - for _, pred := range b.Preds { - x.And(&x, &D[pred.Index]) - } - x.SetBit(&x, i, 1) // a block always dominates itself. - if D[i].Cmp(&x) != 0 { - D[i].Set(&x) - changed = true - } - } - } - - // Check the entire relation. O(n^2). - // The Recover block (if any) must be treated specially so we skip it. - ok := true - for i := 0; i < n; i++ { - for j := 0; j < n; j++ { - b, c := f.Blocks[i], f.Blocks[j] - if c == f.Recover { - continue - } - actual := b.Dominates(c) - expected := D[j].Bit(i) == 1 - if actual != expected { - fmt.Fprintf(os.Stderr, "dominates(%s, %s)==%t, want %t\n", b, c, actual, expected) - ok = false - } - } - } - - preorder := f.DomPreorder() - for _, b := range f.Blocks { - if got := preorder[b.dom.pre]; got != b { - fmt.Fprintf(os.Stderr, "preorder[%d]==%s, want %s\n", b.dom.pre, got, b) - ok = false - } - } - - if !ok { - panic("sanityCheckDomTree failed for " + f.String()) - } - -} - -// Printing functions ---------------------------------------- - -// printDomTree prints the dominator tree as text, using indentation. -func printDomTreeText(buf *bytes.Buffer, v *BasicBlock, indent int) { - fmt.Fprintf(buf, "%*s%s\n", 4*indent, "", v) - for _, child := range v.dom.children { - printDomTreeText(buf, child, indent+1) - } -} - -// printDomTreeDot prints the dominator tree of f in AT&T GraphViz -// (.dot) format. -func printDomTreeDot(buf *bytes.Buffer, f *Function) { - fmt.Fprintln(buf, "//", f) - fmt.Fprintln(buf, "digraph domtree {") - for i, b := range f.Blocks { - v := b.dom - fmt.Fprintf(buf, "\tn%d [label=\"%s (%d, %d)\",shape=\"rectangle\"];\n", v.pre, b, v.pre, v.post) - // TODO(adonovan): improve appearance of edges - // belonging to both dominator tree and CFG. - - // Dominator tree edge. - if i != 0 { - fmt.Fprintf(buf, "\tn%d -> n%d [style=\"solid\",weight=100];\n", v.idom.dom.pre, v.pre) - } - // CFG edges. - for _, pred := range b.Preds { - fmt.Fprintf(buf, "\tn%d -> n%d [style=\"dotted\",weight=0];\n", pred.dom.pre, v.pre) - } - } - fmt.Fprintln(buf, "}") -} |