Failed to deduce type of memset with optimization level > 0

Hi team,

I get the following error as long as I set a non-zero optimization level:

```
/root/.freetensor/BDqwP0/run.cpp:83:48: error: Enzyme: failed to deduce type of memset call void @llvm.memset.p0i8.i64(i8* nonnull align 16 dereferenceable(40000) getelementptr inbounds ([304640 x i8], [304640 x i8]* @_ZZ3runE13__sharedStack, i64 0, i64 160384), i8 0, i64 40000, i1 false) #12, !dbg !1710
_y__4[((_i__31 * 5) + _i__32)] = 0;
^
```

Here, `_y__4` is defined as `auto &&_y__4 = ((double*)(&__sharedStack[160384]));`, and `__sharedStack` is a raw buffer, which is always cast to pointer-to-double to use.

This zeroing statement is in a loop. I guess it is optimized to be a integer `memset` with optimization levels, and Enzyme failed to recognize it.

The full error message is attached, because it has reached the limit of GitHub comments. [log.txt](https://github.com/EnzymeAD/Enzyme/files/11620723/log.txt)

Sorry I don't have a minimal reproduction. I can attach `/tmp/run-11a9c9.cpp` and `/tmp/run-11a9c9.sh` prepared by Clang if you need.

Tested with Enzyme 0.0.66 and Clang 12, with ClangEnzyme.

Thanks in advance.