cmd/compile: use shared dom tree for cse, too

Missed this in the previous CL where the shared
dom tree was introduced.

Change-Id: If0bd85d4b4567d7e87814ed511603b1303ab3903
Reviewed-on: https://go-review.googlesource.com/21970
Run-TryBot: Alexandru Moșoi <alexandru@mosoi.ro>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/ssa/compile.go

@@ -233,8 +233,8 @@ var passes = [...]pass{
 	{name: "opt", fn: opt, required: true},               // TODO: split required rules and optimizing rules
 	{name: "zero arg cse", fn: zcse, required: true},     // required to merge OpSB values
 	{name: "opt deadcode", fn: deadcode, required: true}, // remove any blocks orphaned during opt
-	{name: "generic cse", fn: cse},
 	{name: "generic domtree", fn: domTree},
+	{name: "generic cse", fn: cse},
 	{name: "phiopt", fn: phiopt},
 	{name: "nilcheckelim", fn: nilcheckelim},
 	{name: "prove", fn: prove},
@@ -289,7 +289,8 @@ var passOrder = [...]constraint{
 	{"opt", "nilcheckelim"},
 	// tighten should happen before lowering to avoid splitting naturally paired instructions such as CMP/SET
 	{"tighten", "lower"},
-	// nilcheckelim, prove and loopbce share idom.
+	// cse, nilcheckelim, prove and loopbce share idom.
+	{"generic domtree", "generic cse"},
 	{"generic domtree", "nilcheckelim"},
 	{"generic domtree", "prove"},
 	{"generic domtree", "loopbce"},

src/cmd/compile/internal/ssa/cse.go

@@ -131,9 +131,7 @@ func cse(f *Func) {
 		}
 	}
 
-	// Compute dominator tree
-	idom := dominators(f)
-	sdom := newSparseTree(f, idom)
+	// Dominator tree (f.sdom) is computed by the generic domtree pass.
 
 	// Compute substitutions we would like to do. We substitute v for w
 	// if v and w are in the same equivalence class and v dominates w.
@@ -143,7 +141,7 @@ func cse(f *Func) {
 			// Find a maximal dominant element in e
 			v := e[0]
 			for _, w := range e[1:] {
-				if sdom.isAncestorEq(w.Block, v.Block) {
+				if f.sdom.isAncestorEq(w.Block, v.Block) {
 					v = w
 				}
 			}
@@ -153,7 +151,7 @@ func cse(f *Func) {
 				w := e[i]
 				if w == v {
 					e, e[i] = e[:len(e)-1], e[len(e)-1]
-				} else if sdom.isAncestorEq(v.Block, w.Block) {
+				} else if f.sdom.isAncestorEq(v.Block, w.Block) {
 					rewrite[w.ID] = v
 					e, e[i] = e[:len(e)-1], e[len(e)-1]
 				} else {

src/cmd/compile/internal/ssa/cse_test.go

@@ -44,6 +44,7 @@ func TestCSEAuxPartitionBug(t *testing.T) {
 			Exit("rstore")))
 
 	CheckFunc(fun.f)
+	domTree(fun.f)
 	cse(fun.f)
 	deadcode(fun.f)
 	CheckFunc(fun.f)