unsafe fn probe_index(
        &mut self,
        builder: LLVMBuilderRef,
        value: LLVMValueRef,
        capacity: LLVMValueRef,
    ) -> LLVMValueRef {
        let tmp = LLVMBuildSub(builder, capacity, self.i64(1), c_str!(""));
        LLVMBuildAnd(builder, value, tmp, c_str!(""))
    }
Returns the probe index for an index value by computing the mod.

For a power-of-2 hash table, this is `value & (capacity - 1)`.
weld/src/codegen/llvm2/dict.rs