Optimizing: LoadString may not have any side effects.
LoadString does not have any side effects if the string is
known to be in the dex cache or it's a boot image string
referenced directly, as specified by the string load kind.
We need to clear the side effects for these cases to avoid
a DCHECK() failure when such LoadString instruction ends up
between a ClinitCheck and an instruction to which we want to
merge that ClinitCheck. This may happen as a consequence of
inlining, LICM and DCE as shown by a regression test.
Bug: 27929914
(cherry picked from commit ace7a000a433ce4ecf94f30adea39c01a76fa936)
Change-Id: Iaf9c63b6e58aae1e246b43ca52eea0b47a6ad565
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index 679c274..5f3cdcf 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -2399,6 +2399,7 @@
}
if (!NeedsEnvironment()) {
RemoveEnvironment();
+ SetSideEffects(SideEffects::None());
}
}
diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h
index 10a51d6..56d6a98 100644
--- a/compiler/optimizing/nodes.h
+++ b/compiler/optimizing/nodes.h
@@ -5549,6 +5549,7 @@
SetPackedFlag<kFlagIsInDexCache>(true);
DCHECK(!NeedsEnvironment());
RemoveEnvironment();
+ SetSideEffects(SideEffects::None());
}
size_t InputCount() const OVERRIDE {
diff --git a/test/594-load-string-regression/expected.txt b/test/594-load-string-regression/expected.txt
new file mode 100644
index 0000000..365b0e1
--- /dev/null
+++ b/test/594-load-string-regression/expected.txt
@@ -0,0 +1 @@
+String: ""
diff --git a/test/594-load-string-regression/info.txt b/test/594-load-string-regression/info.txt
new file mode 100644
index 0000000..6a07ace
--- /dev/null
+++ b/test/594-load-string-regression/info.txt
@@ -0,0 +1,2 @@
+Regression test for LoadString listing side effects when it doesn't have any
+and triggering a DCHECK() failure when merging ClinitCheck into NewInstance.
diff --git a/test/594-load-string-regression/src/Main.java b/test/594-load-string-regression/src/Main.java
new file mode 100644
index 0000000..0b9f7b5
--- /dev/null
+++ b/test/594-load-string-regression/src/Main.java
@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+public class Main {
+ static boolean doThrow = false;
+
+ // Note: We're not doing checker tests as we cannot do them specifically for a non-PIC
+ // configuration. The check here would be "prepare_for_register_allocation (before)"
+ // CHECK: LoadClass
+ // CHECK-NEXT: ClinitCheck
+ // CHECK-NEXT: LoadString load_kind:BootImageAddress
+ // CHECK-NEXT: NewInstance
+ // and "prepare_for_register_allocation (after)"
+ // CHECK: LoadString
+ // CHECK-NEXT: NewInstance
+ // but the order of instructions for non-PIC mode is different.
+ public static int $noinline$test() {
+ if (doThrow) { throw new Error(); }
+
+ int r = 0x12345678;
+ do {
+ // LICM pulls the LoadClass and ClinitCheck out of the loop, leaves NewInstance in the loop.
+ Helper h = new Helper();
+ // For non-PIC mode, LICM pulls the boot image LoadString out of the loop.
+ // (For PIC mode, the LoadString can throw and will not be moved out of the loop.)
+ String s = ""; // Empty string is known to be in the boot image.
+ r = r ^ (r >> 5);
+ h.$noinline$printString(s);
+ // During DCE after inlining, the loop back-edge disappears and the pre-header is
+ // merged with the body, leaving consecutive LoadClass, ClinitCheck, LoadString
+ // and NewInstance in non-PIC mode. The prepare_for_register_allocation pass
+ // merges the LoadClass and ClinitCheck with the NewInstance and checks that
+ // there are no instructions with side effects in between. This check used to
+ // fail because LoadString was always listing SideEffects::CanTriggerGC() even
+ // when it doesn't really have any side effects, i.e. for direct references to
+ // boot image Strings or for Strings known to be in the dex cache.
+ } while ($inline$shouldContinue());
+ return r;
+ }
+
+ static boolean $inline$shouldContinue() {
+ return false;
+ }
+
+ public static void main(String[] args) {
+ assertIntEquals(0x12345678 ^ (0x12345678 >> 5), $noinline$test());
+ }
+
+ public static void assertIntEquals(int expected, int result) {
+ if (expected != result) {
+ throw new Error("Expected: " + expected + ", found: " + result);
+ }
+ }
+}
+
+class Helper {
+ static boolean doThrow = false;
+
+ public void $noinline$printString(String s) {
+ if (doThrow) { throw new Error(); }
+
+ System.out.println("String: \"" + s + "\"");
+ }
+}
