52 lines
1.8 KiB
Markdown
52 lines
1.8 KiB
Markdown
|
# Checking the generated assembly #
|
||
|
|
|
||
|
|
## The test ##
|
||
|
|
In `asm_test.cpp` you can find a small program that asks the user for three
|
||
|
|
input floats. The program will add these values together and use the int result
|
||
|
|
as its return value. You can compile different versions of this program so you
|
||
|
|
can compare the binaries: with or without VectorWrapper (`-DWITH_VWR`) and
|
||
|
|
using `std::array` (`-DUSE_STD_ARRAY`) (which will force VectorWrapper's
|
||
|
|
implementation to go through the `get_at()` implementation rather than using
|
||
|
|
the offset-based one) or using just a plain struct. Please have a look at the
|
||
|
|
source code, it's very short.
|
||
|
|
|
||
|
|
## Compiling ##
|
||
|
|
You can compile four different binaries with the following commands:
|
||
|
|
|
||
|
|
```
|
||
|
|
g++ -o bin_vwr -O3 -std=gnu++14 asm_test.cpp -DWITH_VWR
|
||
|
|
g++ -o bin_vwr_array -O3 -std=gnu++14 asm_test.cpp -DWITH_VWR -DUSE_STD_ARRAY
|
||
|
|
g++ -o bin_plain -O3 -std=gnu++14 asm_test.cpp
|
||
|
|
g++ -o bin_plain_array -O3 -std=gnu++14 asm_test.cpp -DUSE_STD_ARRAY
|
||
|
|
```
|
||
|
|
|
||
|
|
* bin_vwr will use VectorWrapper and the custom struct (offset based accessors)
|
||
|
|
* bin_vwr_array will use VectorWrapper and `std::array` (`get_at()` method
|
||
|
|
based accessors)
|
||
|
|
* bin_plain will use the custom struct directly, without VectorWrapper
|
||
|
|
* bin_plain_array will use `std::array` directly, without VectorWrapper
|
||
|
|
|
||
|
|
## Running ##
|
||
|
|
An input file is provided for convenience. You can run each binary like:
|
||
|
|
|
||
|
|
```
|
||
|
|
./bin_vwr < sample_input.txt
|
||
|
|
```
|
||
|
|
|
||
|
|
but of course using a debugger will give you some insight:
|
||
|
|
|
||
|
|
```
|
||
|
|
gdb ./bin_vwr
|
||
|
|
break main
|
||
|
|
layout asm
|
||
|
|
run < sample_input.txt
|
||
|
|
ni
|
||
|
|
...
|
||
|
|
```
|
||
|
|
|
||
|
|
## Results ##
|
||
|
|
On my system (amd64, g++ 8.3.0) this generates four identical binaries (you can
|
||
|
|
check their hash). Feel free to insert bad syntax in the code to make sure that
|
||
|
|
you're indeed compiling different ifdef branches. This is enough to say that at
|
||
|
|
least in this simple case VectorWrapper has no overhead.
|