$ cat $LLVM_HOME/tools/clang/lib/Basic/Targets.cpp
...
    ARCompactTargetInfo(const std::string& triple) : TargetInfo(triple) {
      // Set the default information variables.
      // Mostly taken from ARC GCC manual, some guessed from other targets.

      BigEndian = false;
      TLSSupported = false;
      NoAsmVariants = false;

      PointerWidth = PointerAlign = 32;
      BoolWidth = BoolAlign = 8;
      IntWidth = IntAlign = 32;
      LongWidth = LongAlign = 32;
      LongLongWidth = 64; LongLongAlign = 32;
      // TODO: Check this. I believe Suitable Align is an align for anything, so 32 should do.
      SuitableAlign = 32;
      HalfWidth = HalfAlign = 16;
      FloatWidth = FloatAlign = 32;
      DoubleWidth = 64; DoubleAlign = 32;
      LongDoubleWidth = 64; LongDoubleAlign = 32;

      // Most of this stuff is probably unsupported.
      LargeArrayMinWidth = 0;
      LargeArrayAlign = 0;
      MaxAtomicPromoteWidth = MaxAtomicInlineWidth = 0;

      // Type information.
      SizeType = UnsignedInt;
      PtrDiffType = SignedInt;
      IntMaxType = SignedLongLong;
      UIntMaxType = UnsignedLongLong;
      IntPtrType = SignedInt;
      WCharType = SignedInt; // Not sure if correct.
      WIntType = SignedInt; // Not sure if correct.
      Char16Type = UnsignedShort;
      Char32Type = UnsignedInt;
      Int64Type = SignedLongLong; // Not sure if correct.
      SigAtomicType = SignedInt; // Not sure if correct.

      DescriptionString = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-"
                          "i64:32:32:32-f32:32:32:32-f64:32:32:32-n32";
      UserLabelPrefix = "_"; // TODO: Check.
    }
...
$ cat test.c
int main() {
  double x = 5.5;
  return 0;
}
$ clang -ccc-host-triple arcompact -O0 test.c -emit-llvm -S -o test.ll
$ cat test.ll
; ModuleID = 'test.c'
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:32:32-f32:32:32:32-f64:32:32:32-n32"
target triple = "arcompact"

define i32 @main() nounwind {
entry:
  %retval = alloca i32, align 4
  %x = alloca double, align 8  <---- why does this happen?
  store i32 0, i32* %retval
  store double 5.500000e+00, double* %x, align 8  <---- why does this happen?
  ret i32 0
}