[dev.ssa] cmd/compile/ssa: don't perform nilcheck on OpAddr/OpAddPtr values

Don't nilcheck values that were constructed as a result of OpAddr or
OpAddPtr.

Change-Id: I38053e905d1b76a2a64e77f84e444d38a5217108
Reviewed-on: https://go-review.googlesource.com/13256Reviewed-by: David Chase <drchase@google.com>

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

@@ -53,6 +53,19 @@ func nilcheckelim(f *Func) {
 		var pushRecPtr bool
 		switch node.op {
 		case Work:
+			// a value resulting from taking the address of a
+			// value, or a value constructed from an offset of a
+			// non-nil ptr (OpAddPtr) implies it is non-nil
+			for _, v := range node.block.Values {
+				if v.Op == OpAddr || v.Op == OpAddPtr {
+					// set this immediately instead of
+					// using SetPtr so we can potentially
+					// remove an OpIsNonNil check in the
+					// current work block
+					nonNilValues[v.ID] = true
+				}
+			}
+
 			if node.ptr != nil {
 				// already have a nilcheck in the dominator path
 				if nonNilValues[node.ptr.ID] {

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

@@ -134,9 +134,8 @@ func TestNilcheckDomOrder(t *testing.T) {
 	}
 }
 
-//TODO: Disabled until we track OpAddr constructed values
 // TestNilcheckAddr verifies that nilchecks of OpAddr constructed values are removed.
-func DISABLETestNilcheckAddr(t *testing.T) {
+func TestNilcheckAddr(t *testing.T) {
 	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
 	c := NewConfig("amd64", DummyFrontend{t})
 	fun := Fun(c, "entry",
@@ -168,6 +167,39 @@ func DISABLETestNilcheckAddr(t *testing.T) {
 	}
 }
 
+// TestNilcheckAddPtr verifies that nilchecks of OpAddPtr constructed values are removed.
+func TestNilcheckAddPtr(t *testing.T) {
+	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
+	c := NewConfig("amd64", DummyFrontend{t})
+	fun := Fun(c, "entry",
+		Bloc("entry",
+			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("sb", OpSB, TypeInvalid, 0, nil),
+			Goto("checkPtr")),
+		Bloc("checkPtr",
+			Valu("ptr1", OpAddPtr, ptrType, 0, nil, "sb"),
+			Valu("bool1", OpIsNonNil, TypeBool, 0, nil, "ptr1"),
+			If("bool1", "extra", "exit")),
+		Bloc("extra",
+			Goto("exit")),
+		Bloc("exit",
+			Exit("mem")))
+
+	CheckFunc(fun.f)
+	nilcheckelim(fun.f)
+
+	// clean up the removed nil check
+	fuse(fun.f)
+	deadcode(fun.f)
+
+	CheckFunc(fun.f)
+	for _, b := range fun.f.Blocks {
+		if b == fun.blocks["checkPtr"] && isNilCheck(b) {
+			t.Errorf("checkPtr was not eliminated")
+		}
+	}
+}
+
 // TestNilcheckKeepRemove verifies that dupliate checks of the same pointer
 // are removed, but checks of different pointers are not.
 func TestNilcheckKeepRemove(t *testing.T) {