[dev.typeparams] cmd/compile: fix small -G=3 issues for tests disabled in run.go

 - set correct position for closure capture variable in (*irgen).use()
   (issue20250.go) Also, evaluate rhs, lhs in that order in assignment
   statements to match noder1 (affects ordering of closure variables).

 - make sure to set Assign flag properly in (*irgen).forStmt() for range
   variables which are map accesses (issue9691.go)

 - make sure CheckSize() is call on the base type for top-level types
   converted by (*irgen).typ() that are pointer types (issue20174.go and
   issue37837.go)

 - deal with parentheses properly in validation function
   (*irgen).validate() (issue17270.go)

 - avoid HasNil call on type TTYPEPARAM - types2 typechecker will have
   already checked validity of the typeparam having nil value (new test
   issue39755.go)

Change-Id: Ie68004d964698aea047e19e7dcd79b297e9d47ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/334733
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

7 files changed, 58 insertions, 11 deletions

diff --git a/src/cmd/compile/internal/noder/object.go b/src/cmd/compile/internal/noder/object.go
index 581a3652ec..40c0b9cf42 100644
--- a/src/cmd/compile/internal/noder/object.go
+++ b/src/cmd/compile/internal/noder/object.go
@@ -29,7 +29,7 @@ func (g *irgen) use(name *syntax.Name) *ir.Name {
 	if !ok {
 		base.FatalfAt(g.pos(name), "unknown name %v", name)
 	}
-	obj := ir.CaptureName(g.pos(obj2), ir.CurFunc, g.obj(obj2))
+	obj := ir.CaptureName(g.pos(name), ir.CurFunc, g.obj(obj2))
 	if obj.Defn != nil && obj.Defn.Op() == ir.ONAME {
 		// If CaptureName created a closure variable, then transfer the
 		// type of the captured name to the new closure variable.
diff --git a/src/cmd/compile/internal/noder/stmt.go b/src/cmd/compile/internal/noder/stmt.go
index 672a732187..b7085c4776 100644
--- a/src/cmd/compile/internal/noder/stmt.go
+++ b/src/cmd/compile/internal/noder/stmt.go
@@ -57,7 +57,10 @@ func (g *irgen) stmt(stmt syntax.Stmt) ir.Node {
 			if stmt.Rhs == nil {
 				n = IncDec(g.pos(stmt), op, g.expr(stmt.Lhs))
 			} else {
-				n = ir.NewAssignOpStmt(g.pos(stmt), op, g.expr(stmt.Lhs), g.expr(stmt.Rhs))
+				// Eval rhs before lhs, for compatibility with noder1
+				rhs := g.expr(stmt.Rhs)
+				lhs := g.expr(stmt.Lhs)
+				n = ir.NewAssignOpStmt(g.pos(stmt), op, lhs, rhs)
 			}
 			if n.X.Typecheck() == 3 {
 				n.SetTypecheck(3)
@@ -68,8 +71,9 @@ func (g *irgen) stmt(stmt syntax.Stmt) ir.Node {
 			return n
 		}
 
-		names, lhs := g.assignList(stmt.Lhs, stmt.Op == syntax.Def)
+		// Eval rhs before lhs, for compatibility with noder1
 		rhs := g.exprList(stmt.Rhs)
+		names, lhs := g.assignList(stmt.Lhs, stmt.Op == syntax.Def)
 
 		// We must delay transforming the assign statement if any of the
 		// lhs or rhs nodes are also delayed, since transformAssign needs
@@ -262,6 +266,12 @@ func (g *irgen) forStmt(stmt *syntax.ForStmt) ir.Node {
 		key, value := unpackTwo(lhs)
 		n := ir.NewRangeStmt(g.pos(r), key, value, g.expr(r.X), g.blockStmt(stmt.Body))
 		n.Def = initDefn(n, names)
+		if key != nil {
+			transformCheckAssign(n, key)
+		}
+		if value != nil {
+			transformCheckAssign(n, value)
+		}
 		return n
 	}
 
diff --git a/src/cmd/compile/internal/noder/types.go b/src/cmd/compile/internal/noder/types.go
index d925f991c8..c18ae3a1fc 100644
--- a/src/cmd/compile/internal/noder/types.go
+++ b/src/cmd/compile/internal/noder/types.go
@@ -39,6 +39,11 @@ func (g *irgen) typ(typ types2.Type) *types.Type {
 	// recursive types have been fully constructed before we call CheckSize.
 	if res != nil && !res.IsUntyped() && !res.IsFuncArgStruct() && !res.HasTParam() {
 		types.CheckSize(res)
+		if res.IsPtr() {
+			// Pointers always have their size set, even though their element
+			// may not have its size set.
+			types.CheckSize(res.Elem())
+		}
 	}
 	return res
 }
diff --git a/src/cmd/compile/internal/noder/validate.go b/src/cmd/compile/internal/noder/validate.go
index b926222c89..68a059b96f 100644
--- a/src/cmd/compile/internal/noder/validate.go
+++ b/src/cmd/compile/internal/noder/validate.go
@@ -55,7 +55,15 @@ func (g *irgen) validate(n syntax.Node) {
 	case *syntax.CallExpr:
 		tv := g.info.Types[n.Fun]
 		if tv.IsBuiltin() {
-			switch builtin := n.Fun.(type) {
+			fun := n.Fun
+			for {
+				builtin, ok := fun.(*syntax.ParenExpr)
+				if !ok {
+					break
+				}
+				fun = builtin.X
+			}
+			switch builtin := fun.(type) {
 			case *syntax.Name:
 				g.validateBuiltin(builtin.Value, n)
 			case *syntax.SelectorExpr:
diff --git a/src/cmd/compile/internal/typecheck/iexport.go b/src/cmd/compile/internal/typecheck/iexport.go
index 4fbc48f17b..b054c73ad8 100644
--- a/src/cmd/compile/internal/typecheck/iexport.go
+++ b/src/cmd/compile/internal/typecheck/iexport.go
@@ -1636,7 +1636,9 @@ func (w *exportWriter) expr(n ir.Node) {
 	// (somewhat closely following the structure of exprfmt in fmt.go)
 	case ir.ONIL:
 		n := n.(*ir.NilExpr)
-		if !n.Type().HasNil() {
+		// If n is a typeparam, it will have already been checked
+		// for proper use by the types2 typechecker.
+		if !n.Type().IsTypeParam() && !n.Type().HasNil() {
 			base.Fatalf("unexpected type for nil: %v", n.Type())
 		}
 		w.op(ir.ONIL)
diff --git a/test/run.go b/test/run.go
index 82d49270f2..3ccf1046ce 100644
--- a/test/run.go
+++ b/test/run.go
@@ -2167,12 +2167,7 @@ var types2Failures32Bit = setOf(
 )
 
 var g3Failures = setOf(
-	"writebarrier.go",         // correct diagnostics, but different lines (probably irgen's fault)
-	"fixedbugs/issue17270.go", // ICE in irgen
-	"fixedbugs/issue20174.go", // ICE due to width not calculated (probably irgen's fault)
-	"fixedbugs/issue20250.go", // correct diagnostics, but different lines (probably irgen's fault)
-	"fixedbugs/issue37837.go", // ICE due to width not calculated
-	"fixedbugs/issue9691.go",  // "cannot assign to int(.autotmp_4)" (probably irgen's fault)
+	"writebarrier.go", // correct diagnostics, but different lines (probably irgen's fault)
 
 	"typeparam/nested.go", // -G=3 doesn't support function-local types with generics
 
diff --git a/test/typeparam/issue39755.go b/test/typeparam/issue39755.go
new file mode 100644
index 0000000000..13a575d16f
--- /dev/null
+++ b/test/typeparam/issue39755.go
@@ -0,0 +1,27 @@
+// compile -G=3
+
+// Copyright 2020 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.
+
+// copied from cmd/compile/internal/types2/testdata/fixedbugs/issue39755.go
+
+package p
+
+func _[T interface{~map[string]int}](x T) {
+	_ = x == nil
+}
+
+// simplified test case from issue
+
+type PathParamsConstraint interface {
+        ~map[string]string | ~[]struct{key, value string}
+}
+
+type PathParams[T PathParamsConstraint] struct {
+	t T
+}
+
+func (pp *PathParams[T]) IsNil() bool {
+	return pp.t == nil // this must succeed
+}