MIPS32: Refactor implicit null checks in array/field get/set.

Rationale: on MIPS32 64-bit loads and stores may be performed
as pairs of 32-bit loads/stores. Implicit null checks must be
associated with the first 32-bit load/store in a pair and not
the last. This change ensures proper association of said checks
(a few were done after the last 32-bit load/store in a pair)
and lays ground for further improvements in array/field get/set.

Test: booted MIPS32 in QEMU
Test: test-art-host-gtest
Test: test-art-target-run-test-optimizing in QEMU

Change-Id: I3674947c00bb17930790a7a47c9b7aadc0c030b8
diff --git a/test/551-implicit-null-checks/src/Main.java b/test/551-implicit-null-checks/src/Main.java
index 677e8d3..3586a29 100644
--- a/test/551-implicit-null-checks/src/Main.java
+++ b/test/551-implicit-null-checks/src/Main.java
@@ -18,6 +18,7 @@
 
   private class Inner {
     private long i1;
+    private double i2;
   }
   private Inner inst;
 
@@ -26,12 +27,22 @@
     try {
       m.$opt$noinline$testGetLong();
     } catch (NullPointerException ex) {
-      // good
+      System.out.println("NPE from GetLong");
     }
     try {
       m.$opt$noinline$testPutLong(778899112233L);
     } catch (NullPointerException ex) {
-      // good
+      System.out.println("NPE from PutLong");
+    }
+    try {
+      m.$opt$noinline$testGetDouble();
+    } catch (NullPointerException ex) {
+      System.out.println("NPE from GetDouble");
+    }
+    try {
+      m.$opt$noinline$testPutDouble(1.0);
+    } catch (NullPointerException ex) {
+      System.out.println("NPE from PutDouble");
     }
   }
 
@@ -44,4 +55,14 @@
     inst.i1 = a;
     throw new Exception();  // prevent inline
   }
+
+  public void $opt$noinline$testGetDouble() throws Exception {
+    double result = inst.i2;
+    throw new Exception();  // prevent inline
+  }
+
+  public void $opt$noinline$testPutDouble(double a) throws Exception {
+    inst.i2 = a;
+    throw new Exception();  // prevent inline
+  }
 }