[asan] Remove special case mapping on Android/AArch64.

ASan shadow on Android starts at address 0 for both historic and
performance reasons. This is possible because the platform mandates
-pie, which makes lower memory region always available.

This is not such a good idea on 64-bit platforms because of MAP_32BIT
incompatibility.

This patch changes Android/AArch64 mapping to be the same as that of
Linux/AAarch64.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243548 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -340,12 +340,12 @@ static ShadowMapping getShadowMapping(Triple &TargetTriple, int LongSize,
 
   ShadowMapping Mapping;
 
-  if (IsAndroid) {
+  if (LongSize == 32) {
     // Android is always PIE, which means that the beginning of the address
     // space is always available.
-    Mapping.Offset = 0;
-  } else if (LongSize == 32) {
-    if (IsMIPS32)
+    if (IsAndroid)
+      Mapping.Offset = 0;
+    else if (IsMIPS32)
       Mapping.Offset = kMIPS32_ShadowOffset32;
     else if (IsFreeBSD)
       Mapping.Offset = kFreeBSD_ShadowOffset32;