Incorrect transformation of (sub,neg) to (sub) for fp

A pair (sub,neg) should not be transformed to (sub) for
floating point operations, otherwise we can lose the sign of
zero for instructions like this:
  - (A - B) != B - A if B == A

Change-Id: I4d612612d4dc0a067fac5721ad206f74168bcd36
Signed-off-by: Serguei Katkov <serguei.i.katkov@intel.com>

4 files changed, 55 insertions, 1 deletions

diff --git a/compiler/optimizing/instruction_simplifier.cc b/compiler/optimizing/instruction_simplifier.cc
index afbc490..180bdc9 100644
--- a/compiler/optimizing/instruction_simplifier.cc
+++ b/compiler/optimizing/instruction_simplifier.cc
@@ -424,7 +424,8 @@ void InstructionSimplifierVisitor::VisitNeg(HNeg* instruction) {
     return;
   }
 
-  if (input->IsSub() && input->HasOnlyOneNonEnvironmentUse()) {
+  if (input->IsSub() && input->HasOnlyOneNonEnvironmentUse() &&
+      !Primitive::IsFloatingPointType(input->GetType())) {
     // Replace code looking like
     //    SUB tmp, a, b
     //    NEG dst, tmp
@@ -435,6 +436,7 @@ void InstructionSimplifierVisitor::VisitNeg(HNeg* instruction) {
     // worse code. In particular, we do not want the live ranges of `a` and `b`
     // to be extended if we are not sure the initial 'SUB' instruction can be
     // removed.
+    // We do not perform optimization for fp because we could lose the sign of zero.
     HSub* sub = input->AsSub();
     HSub* new_sub =
         new (GetGraph()->GetArena()) HSub(instruction->GetType(), sub->GetRight(), sub->GetLeft());
diff --git a/test/474-fp-sub-neg/expected.txt b/test/474-fp-sub-neg/expected.txt
new file mode 100644
index 0000000..e6ffe0d
--- /dev/null
+++ b/test/474-fp-sub-neg/expected.txt
@@ -0,0 +1,2 @@
+-0.0
+-0.0
diff --git a/test/474-fp-sub-neg/info.txt b/test/474-fp-sub-neg/info.txt
new file mode 100644
index 0000000..eced93f
--- /dev/null
+++ b/test/474-fp-sub-neg/info.txt
@@ -0,0 +1,5 @@
+Regression check for optimizing simplify instruction pass.
+A pair (sub, neg) should not be transforemd to (sub) for
+fp calculation because we can lose the sign of zero for
+the following expression:
+  - ( A - B ) != B - A ; if B == A
diff --git a/test/474-fp-sub-neg/src/Main.java b/test/474-fp-sub-neg/src/Main.java
new file mode 100644
index 0000000..e6bce67
--- /dev/null
+++ b/test/474-fp-sub-neg/src/Main.java
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2015 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 {
+    public static void floatTest() {
+      float f = 0;
+      float fc = 1f;
+      for (int i = 0; i < 2; i++) {
+        f -= fc;
+        f = -f;
+      }
+
+      System.out.println(f);
+    }
+
+    public static void doubleTest() {
+      double d = 0;
+      double dc = 1f;
+      for (int i = 0; i < 2; i++) {
+        d -= dc;
+        d = -d;
+      }
+
+      System.out.println(d);
+    }
+
+    public static void main(String[] args) {
+        doubleTest();
+        floatTest();
+    }
+
+}