[dev.ssa] cmd/compile: enhance SSA filtering, add OpConvert

Modified GOSSA{HASH.PKG} environment variable filters to
make it easier to make/run with all SSA for testing.
Disable attempts at SSA for architectures that are not
amd64 (avoid spurious errors/unimplementeds.)

Removed easy out for unimplemented features.

Add convert op for proper liveness in presence of uintptr
to/from unsafe.Pointer conversions.

Tweaked stack sizes to get a pass on windows;
1024 instead 768, was observed to pass at least once.

Change-Id: Ida3800afcda67d529e3b1cf48ca4a3f0fa48b2c5
Reviewed-on: https://go-review.googlesource.com/16201
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/pgen.go

@@ -414,7 +414,9 @@ func compile(fn *Node) {
 
 	// Build an SSA backend function.
 	// TODO: get rid of usessa.
-	ssafn, usessa = buildssa(Curfn)
+	if Thearch.Thestring == "amd64" {
+		ssafn, usessa = buildssa(Curfn)
+	}
 
 	continpc = nil
 	breakpc = nil

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

@@ -24,8 +24,32 @@ import (
 // it will never return nil, and the bool can be removed.
 func buildssa(fn *Node) (ssafn *ssa.Func, usessa bool) {
 	name := fn.Func.Nname.Sym.Name
+	gossahash := os.Getenv("GOSSAHASH")
 	usessa = strings.HasSuffix(name, "_ssa") || strings.Contains(name, "_ssa.") || name == os.Getenv("GOSSAFUNC")
 
+	// Environment variable control of SSA CG
+	// 1. IF GOSSAFUNC == current function name THEN
+	//       compile this function with SSA and log output to ssa.html
+
+	// 2. IF GOSSAHASH == "y" or "Y" THEN
+	//       compile this function (and everything else) with SSA
+
+	// 3. IF GOSSAHASH == "" THEN
+	//       IF GOSSAPKG == current package name THEN
+	//          compile this function (and everything in this package) with SSA
+	//       ELSE
+	//          use the old back end for this function.
+	//       This is for compatibility with existing test harness and should go away.
+
+	// 4. IF GOSSAHASH is a suffix of the binary-rendered SHA1 hash of the function name THEN
+	//          compile this function with SSA
+	//       ELSE
+	//          compile this function with the old back end.
+
+	// Plan is for 3 to be remove, and the 2) dependence on GOSSAHASH changes
+	// from "y"/"Y" to empty -- then SSA is default, and is disabled by setting
+	// GOSSAHASH to a value that is neither 0 nor 1 (e.g., "N" or "X")
+
 	if usessa {
 		fmt.Println("generating SSA for", name)
 		dumplist("buildssa-enter", fn.Func.Enter)
@@ -58,17 +82,6 @@ func buildssa(fn *Node) (ssafn *ssa.Func, usessa bool) {
 		}
 	}()
 
-	// If SSA support for the function is incomplete,
-	// assume that any panics are due to violated
-	// invariants. Swallow them silently.
-	defer func() {
-		if err := recover(); err != nil {
-			if !e.unimplemented {
-				panic(err)
-			}
-		}
-	}()
-
 	// We construct SSA using an algorithm similar to
 	// Brau, Buchwald, Hack, Leißa, Mallon, and Zwinkau
 	// http://pp.info.uni-karlsruhe.de/uploads/publikationen/braun13cc.pdf
@@ -167,27 +180,17 @@ func buildssa(fn *Node) (ssafn *ssa.Func, usessa bool) {
 	// Main call to ssa package to compile function
 	ssa.Compile(s.f)
 
-	// Calculate stats about what percentage of functions SSA handles.
-	if false {
-		fmt.Printf("SSA implemented: %t\n", !e.unimplemented)
-	}
-
-	if e.unimplemented {
-		return nil, false
-	}
-
-	// TODO: enable codegen more broadly once the codegen stabilizes
-	// and runtime support is in (gc maps, write barriers, etc.)
-	if usessa {
+	if usessa || gossahash == "y" || gossahash == "Y" {
 		return s.f, true
 	}
-	if localpkg.Name != os.Getenv("GOSSAPKG") {
-		return s.f, false
-	}
-	if os.Getenv("GOSSAHASH") == "" {
+	if gossahash == "" {
+		if localpkg.Name != os.Getenv("GOSSAPKG") {
+			return s.f, false
+		}
 		// Use everything in the package
 		return s.f, true
 	}
+
 	// Check the hash of the name against a partial input hash.
 	// We use this feature to do a binary search within a package to
 	// find a function that is incorrectly compiled.
@@ -195,10 +198,26 @@ func buildssa(fn *Node) (ssafn *ssa.Func, usessa bool) {
 	for _, b := range sha1.Sum([]byte(name)) {
 		hstr += fmt.Sprintf("%08b", b)
 	}
-	if strings.HasSuffix(hstr, os.Getenv("GOSSAHASH")) {
+
+	if strings.HasSuffix(hstr, gossahash) {
 		fmt.Printf("GOSSAHASH triggered %s\n", name)
 		return s.f, true
 	}
+
+	// Iteratively try additional hashes to allow tests for multi-point
+	// failure.
+	for i := 0; true; i++ {
+		ev := fmt.Sprintf("GOSSAHASH%d", i)
+		evv := os.Getenv(ev)
+		if evv == "" {
+			break
+		}
+		if strings.HasSuffix(hstr, evv) {
+			fmt.Printf("%s triggered %s\n", ev, name)
+			return s.f, true
+		}
+	}
+
 	return s.f, false
 }
 
@@ -1353,6 +1372,15 @@ func (s *state) expr(n *Node) *ssa.Value {
 		// Assume everything will work out, so set up our return value.
 		// Anything interesting that happens from here is a fatal.
 		x := s.expr(n.Left)
+
+		// Special case for not confusing GC and liveness.
+		// We don't want pointers accidentally classified
+		// as not-pointers or vice-versa because of copy
+		// elision.
+		if to.IsPtr() != from.IsPtr() {
+			return s.newValue1(ssa.OpConvert, to, x)
+		}
+
 		v := s.newValue1(ssa.OpCopy, to, x) // ensure that v has the right type
 
 		// CONVNOP closure
@@ -1364,6 +1392,7 @@ func (s *state) expr(n *Node) *ssa.Value {
 		if from.Etype == to.Etype {
 			return v
 		}
+
 		// unsafe.Pointer <--> *T
 		if to.Etype == TUNSAFEPTR && from.IsPtr() || from.Etype == TUNSAFEPTR && to.IsPtr() {
 			return v

src/cmd/compile/internal/ssa/gen/AMD64.rules

@@ -281,6 +281,9 @@
 (Store [2] ptr val mem) -> (MOVWstore ptr val mem)
 (Store [1] ptr val mem) -> (MOVBstore ptr val mem)
 
+// We want this to stick out so the to/from ptr conversion is obvious
+(Convert <t> x) -> (LEAQ <t> x)
+
 // checks
 (IsNonNil p) -> (SETNE (TESTQ p p))
 (IsInBounds idx len) -> (SETB (CMPQ idx len))

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

@@ -237,8 +237,9 @@ var genericOps = []opData{
 	{name: "Sqrt"}, // sqrt(arg0), float64 only
 
 	// Data movement
-	{name: "Phi"},  // select an argument based on which predecessor block we came from
-	{name: "Copy"}, // output = arg0
+	{name: "Phi"},     // select an argument based on which predecessor block we came from
+	{name: "Copy"},    // output = arg0
+	{name: "Convert"}, // output = arg0 -- a copy that converts to/from a pointer
 
 	// constants.  Constant values are stored in the aux field.
 	// booleans have a bool aux field, strings have a string aux

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

@@ -455,6 +455,7 @@ const (
 	OpSqrt
 	OpPhi
 	OpCopy
+	OpConvert
 	OpConstBool
 	OpConstString
 	OpConstNil
@@ -3866,6 +3867,10 @@ var opcodeTable = [...]opInfo{
 		name:    "Copy",
 		generic: true,
 	},
+	{
+		name:    "Convert",
+		generic: true,
+	},
 	{
 		name:    "ConstBool",
 		generic: true,

src/cmd/compile/internal/ssa/rewriteAMD64.go

@@ -1670,6 +1670,24 @@ func rewriteValueAMD64(v *Value, config *Config) bool {
 		goto endc395c0a53eeccf597e225a07b53047d1
 	endc395c0a53eeccf597e225a07b53047d1:
 		;
+	case OpConvert:
+		// match: (Convert <t> x)
+		// cond:
+		// result: (LEAQ <t> x)
+		{
+			t := v.Type
+			x := v.Args[0]
+			v.Op = OpAMD64LEAQ
+			v.AuxInt = 0
+			v.Aux = nil
+			v.resetArgs()
+			v.Type = t
+			v.AddArg(x)
+			return true
+		}
+		goto end1cac40a6074914d6ae3d4aa039a625ed
+	end1cac40a6074914d6ae3d4aa039a625ed:
+		;
 	case OpCvt32Fto32:
 		// match: (Cvt32Fto32 x)
 		// cond:

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

@@ -54,8 +54,12 @@ func tighten(f *Func) {
 		for _, b := range f.Blocks {
 			for i := 0; i < len(b.Values); i++ {
 				v := b.Values[i]
-				if v.Op == OpPhi || v.Op == OpGetClosurePtr {
-					// GetClosurePtr must stay in entry block
+				if v.Op == OpPhi || v.Op == OpGetClosurePtr || v.Op == OpConvert {
+					// GetClosurePtr must stay in entry block.
+					// OpConvert must not float over call sites.
+					// TODO do we instead need a dependence edge of some sort for OpConvert?
+					// Would memory do the trick, or do we need something else that relates
+					// to safe point operations?
 					continue
 				}
 				if len(v.Args) > 0 && v.Args[len(v.Args)-1].Type.IsMemory() {

src/cmd/dist/test.go

@@ -278,11 +278,6 @@ func (t *tester) registerStdTest(pkg string) {
 
 // TODO: Remove when SSA codegen is used by default.
 func (t *tester) registerSSATest(pkg string) {
-	switch pkg {
-	// known failures
-	case "runtime":
-		return
-	}
 	t.tests = append(t.tests, distTest{
 		name:    "go_test_ssa:" + pkg,
 		heading: "Testing packages with SSA codegen.",

src/cmd/internal/obj/stack.go

@@ -41,7 +41,7 @@ const (
 	STACKSYSTEM = 0
 	StackSystem = STACKSYSTEM
 	StackBig    = 4096
-	StackGuard  = 640*stackGuardMultiplier + StackSystem
+	StackGuard  = 1024*stackGuardMultiplier + StackSystem
 	StackSmall  = 128
 	StackLimit  = StackGuard - StackSystem - StackSmall
 )

src/cmd/internal/obj/util.go

@@ -385,6 +385,9 @@ func Dconv(p *Prog, a *Addr) string {
 		if a.Index != REG_NONE {
 			str += fmt.Sprintf("(%v*%d)", Rconv(int(a.Index)), int(a.Scale))
 		}
+		if p.As == ATYPE && a.Gotype != nil {
+			str += fmt.Sprintf("%s", a.Gotype.Name)
+		}
 
 	case TYPE_CONST:
 		if a.Reg != 0 {

src/runtime/stack.go

@@ -86,7 +86,7 @@ const (
 
 	// The stack guard is a pointer this many bytes above the
 	// bottom of the stack.
-	_StackGuard = 640*stackGuardMultiplier + _StackSystem
+	_StackGuard = 1024*stackGuardMultiplier + _StackSystem
 
 	// After a stack split check the SP is allowed to be this
 	// many bytes below the stack guard.  This saves an instruction

test/nosplit.go

@@ -9,6 +9,7 @@ package main
 
 import (
 	"bytes"
+	"cmd/internal/obj"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -285,12 +286,13 @@ TestCases:
 				// Instead of rewriting the test cases above, adjust
 				// the first stack frame to use up the extra bytes.
 				if i == 0 {
-					size += 512 - 128
+					size += (obj.StackGuard - 128) - 128
 					// Noopt builds have a larger stackguard.
-					// See ../cmd/dist/buildruntime.go:stackGuardMultiplier
+					// See ../src/cmd/dist/buildruntime.go:stackGuardMultiplier
+					// This increase is included in obj.StackGuard
 					for _, s := range strings.Split(os.Getenv("GO_GCFLAGS"), " ") {
 						if s == "-N" {
-							size += 640
+							size += obj.StackGuard
 						}
 					}
 				}