cmd/compile/internal/ssa: eliminate string copies for calls to unique.Make

unique.Make always copies strings passed into it, so it's safe to not
copy byte slices converted to strings either. Handle this just like map
accesses with string(b) as keys.

This CL only handles unique.Make(string(b)), not nested cases like
unique.Make([2]string{string(b1), string(b2)}); this could be done in a
followup CL but the map lookup code in walk is sufficiently different
than the call handling code that I didn't attempt it. (SSA is much
easier).

Fixes #71926

Change-Id: Ic2f82f2f91963d563b4ddb1282bd49fc40da8b85
Reviewed-on: https://go-review.googlesource.com/c/go/+/672135
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/compile/internal/ssa/_gen/generic.rules

@@ -2832,3 +2832,14 @@
   && clobber(sbts)
   && clobber(key)
 => (StaticLECall {f} [argsize] typ_ map_ (StringMake <typ.String> ptr len) mem)
+
+// Similarly to map lookups, also handle unique.Make for strings, which unique.Make will clone.
+(StaticLECall {f} [argsize] dict_ key:(SelectN [0] sbts:(StaticLECall {g} _ ptr len mem)) m:(SelectN [1] sbts))
+  && isSameCall(f, "unique.Make[go.shape.string]")
+  && isSameCall(g, "runtime.slicebytetostring")
+  && key.Uses == 1
+  && sbts.Uses == 2
+  && resetCopy(m, mem)
+  && clobber(sbts)
+  && clobber(key)
+=> (StaticLECall {f} [argsize] dict_ (StringMake <typ.String> ptr len) mem)

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

@@ -30743,6 +30743,41 @@ func rewriteValuegeneric_OpStaticLECall(v *Value) bool {
 		v.AddArg4(typ_, map_, v0, mem)
 		return true
 	}
+	// match: (StaticLECall {f} [argsize] dict_ key:(SelectN [0] sbts:(StaticLECall {g} _ ptr len mem)) m:(SelectN [1] sbts))
+	// cond: isSameCall(f, "unique.Make[go.shape.string]") && isSameCall(g, "runtime.slicebytetostring") && key.Uses == 1 && sbts.Uses == 2 && resetCopy(m, mem) && clobber(sbts) && clobber(key)
+	// result: (StaticLECall {f} [argsize] dict_ (StringMake <typ.String> ptr len) mem)
+	for {
+		if len(v.Args) != 3 {
+			break
+		}
+		argsize := auxIntToInt32(v.AuxInt)
+		f := auxToCall(v.Aux)
+		_ = v.Args[2]
+		dict_ := v.Args[0]
+		key := v.Args[1]
+		if key.Op != OpSelectN || auxIntToInt64(key.AuxInt) != 0 {
+			break
+		}
+		sbts := key.Args[0]
+		if sbts.Op != OpStaticLECall || len(sbts.Args) != 4 {
+			break
+		}
+		g := auxToCall(sbts.Aux)
+		mem := sbts.Args[3]
+		ptr := sbts.Args[1]
+		len := sbts.Args[2]
+		m := v.Args[2]
+		if m.Op != OpSelectN || auxIntToInt64(m.AuxInt) != 1 || sbts != m.Args[0] || !(isSameCall(f, "unique.Make[go.shape.string]") && isSameCall(g, "runtime.slicebytetostring") && key.Uses == 1 && sbts.Uses == 2 && resetCopy(m, mem) && clobber(sbts) && clobber(key)) {
+			break
+		}
+		v.reset(OpStaticLECall)
+		v.AuxInt = int32ToAuxInt(argsize)
+		v.Aux = callToAux(f)
+		v0 := b.NewValue0(v.Pos, OpStringMake, typ.String)
+		v0.AddArg2(ptr, len)
+		v.AddArg3(dict_, v0, mem)
+		return true
+	}
 	return false
 }
 func rewriteValuegeneric_OpStore(v *Value) bool {

src/unique/handle_test.go

@@ -233,7 +233,7 @@ func TestMakeAllocs(t *testing.T) {
 			stringHandle = Make(string(b[:]))
 		}},
 
-		{name: "bytes", allocs: 1, f: func() {
+		{name: "bytes", allocs: 0, f: func() {
 			stringHandle = Make(string(heapBytes))
 		}},
 
@@ -241,7 +241,7 @@ func TestMakeAllocs(t *testing.T) {
 			stringHandle = Make(string(heapBytes[:16]))
 		}},
 
-		{name: "bytes truncated long", allocs: 1, f: func() {
+		{name: "bytes truncated long", allocs: 0, f: func() {
 			stringHandle = Make(string(heapBytes[:40]))
 		}},
 

test/codegen/unique.go

@@ -0,0 +1,24 @@
+// asmcheck
+
+// Copyright 2015 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 codegen
+
+import "unique"
+
+func BytesToHandle(b []byte) unique.Handle[string] {
+	// amd64:-`.*runtime\.slicebytetostring\(`
+	return unique.Make(string(b))
+}
+
+type Pair struct {
+	S1 string
+	S2 string
+}
+
+func BytesPairToHandle(b1, b2 []byte) unique.Handle[Pair] {
+	// TODO: should not copy b1 and b2.
+	return unique.Make(Pair{string(b1), string(b2)})
+}