Use constant length for memcpy on A64 simulator.

src/a64/simulator-a64.h

Index: src/a64/simulator-a64.h
diff --git a/src/a64/simulator-a64.h b/src/a64/simulator-a64.h
index 959644b773e21bec17eea32c840ebd413fc799c2..eaff71c20d669c88a8aa502c362488a18ce2ec6e 100644
--- a/src/a64/simulator-a64.h
+++ b/src/a64/simulator-a64.h
@@ -168,8 +168,14 @@ class SimRegisterBase {
     ASSERT(size <= sizeof(new_value));
     // All AArch64 registers are zero-extending; Writing a W register clears the
     // top bits of the corresponding X register.
-    memset(value_, 0, kSizeInBytes);
-    memcpy(value_, &new_value, size);
+    if (size == kXRegSize) {

[Rodolph Perfetta, 2014/03/20 11:33:57]

STATIC_ASSERT(kXRegSize == kDRegSize);

This is more to document the fact this is also used for S and D registers

same below with W and S

[Fritz, 2014/03/20 19:37:01]

Done.

+      memcpy(value_, &new_value, kXRegSize);
+    } else if (size == kWRegSize) {
+      memset(value_, 0, kSizeInBytes);
+      memcpy(value_, &new_value, kWRegSize);
+    } else {
+      UNREACHABLE();
+    }
   }
 
   // Copy 'size' bytes of the register to the result, and zero-extend to fill
@@ -179,7 +185,13 @@ class SimRegisterBase {
     ASSERT(size <= kSizeInBytes);
     T result;
     memset(&result, 0, sizeof(result));

[Sven Panne, 2014/03/20 10:22:38]

I think this could be moved into the 2nd case, just like Set.

[Fritz, 2014/03/20 19:37:01]

Done.

-    memcpy(&result, value_, size);
+    if (size == kXRegSize) {
+      memcpy(&result, value_, kXRegSize);
+    } else if (size == kWRegSize) {
+      memcpy(&result, value_, kWRegSize);
+    } else {
+      UNREACHABLE();
+    }
     return result;
   }