Eliminate redundant bitwise operations when using a llvm/ADT/PointerUnion.

Eliminate redundant bitwise operations when using a llvm/ADT/PointerUnion.

For comparison, with this code sample:

PointerUnion<int *, char *> Data;
PointerUnion<int *, char *> foo1() {
	Data = new int;
	return new int;
}
PointerUnion<int *, char *> foo2() {
	Data = new char;
	return new char;
}

Before this patch we would get:

define i64 @_Z4foo1v() uwtable ssp {
  %1 = tail call noalias i8* @_Znwm(i64 4)
  %2 = ptrtoint i8* %1 to i64
  %3 = load i64* getelementptr inbounds (%"class.llvm::PointerUnion"* @Data, i64 0, i32 0, i32 0), align 8
  %4 = and i64 %3, 1
  %.masked.i = and i64 %2, -3
  %5 = or i64 %4, %.masked.i
  store i64 %5, i64* getelementptr inbounds (%"class.llvm::PointerUnion"* @Data, i64 0, i32 0, i32 0), align 8
  %6 = tail call noalias i8* @_Znwm(i64 4)
  %7 = ptrtoint i8* %6 to i64
  %8 = and i64 %7, -3
  ret i64 %8
}

define i64 @_Z4foo2v() uwtable ssp {
  %1 = tail call noalias i8* @_Znwm(i64 1)
  %2 = ptrtoint i8* %1 to i64
  %3 = load i64* getelementptr inbounds (%"class.llvm::PointerUnion"* @Data, i64 0, i32 0, i32 0), align 8
  %4 = and i64 %3, 1
  %5 = or i64 %2, %4
  %6 = or i64 %5, 2
  store i64 %6, i64* getelementptr inbounds (%"class.llvm::PointerUnion"* @Data, i64 0, i32 0, i32 0), align 8
  %7 = tail call noalias i8* @_Znwm(i64 1)
  %8 = ptrtoint i8* %7 to i64
  %9 = or i64 %8, 2
  ret i64 %9
}

After the patch:

define i64 @_Z4foo1v() uwtable ssp {
  %1 = tail call noalias i8* @_Znwm(i64 4)
  %2 = ptrtoint i8* %1 to i64
  store i64 %2, i64* getelementptr inbounds (%"class.llvm::PointerUnion"* @Data, i64 0, i32 0, i32 0), align 8
  %3 = tail call noalias i8* @_Znwm(i64 4)
  %4 = ptrtoint i8* %3 to i64
  ret i64 %4
}

declare noalias i8* @_Znwm(i64)

define i64 @_Z4foo2v() uwtable ssp {
  %1 = tail call noalias i8* @_Znwm(i64 1)
  %2 = ptrtoint i8* %1 to i64
  %3 = or i64 %2, 2
  store i64 %3, i64* getelementptr inbounds (%"class.llvm::PointerUnion"* @Data, i64 0, i32 0, i32 0), align 8
  %4 = tail call noalias i8* @_Znwm(i64 1)
  %5 = ptrtoint i8* %4 to i64
  %6 = or i64 %5, 2
  ret i64 %6
}

llvm-svn: 169147