higaski / GccVsClang_uC

GCC vs Clang Cortex-M4 benchmarks

GccVsClang_uC

GccVsClang_uC is a test project for the STM32F4Discovery board which compares binary sizes of usual optimization levels for embedded software (O2, Os and Clang's Oz) between GCC and Clang.

Test cases

GccVsClang_uC currently contains 6 different test cases I copied from other unrelated projects of mine. The macro BUILD inside main.cpp is used to choose the test case.

1. BLINKY

BLINKY toggles all 4 LEDs on the board in an intervall of 1s.

2. HELLO_WORLD

HELLO_WORLD uses SEMIHOSTING to print a "Hello World\n" message to the debugger console.

3. I2C_SLAVE

I2C_SLAVE utilizes the first I2C peripheral (I2C1) of the board to slave transmit some bytes. Each transmission is started by resetting Pin7 of GPIOC.

4. ENCODER

ENCODER initializes TIM3 to run in encoder mode. Pin6 and 7 of GPIOA are used as encoder inputs. The current value of TIM3 is output to the debugger console with SEMIHOSTING.

5. TYPE_TREE_MENU

TYPE_TREE_MENU uses a binary tree made with std::pair to create a browsable menu. The user input is continuously red from serial port USART3 and allows browsing the menu by sending the following characters

• '4' left node
• '6' right node
• '8' previous node
• '0' exit

The current position in the binary tree is sent back on the serial port.

6. LUA

LUA embedds Lua 5.3.4 and runs some Lua code...

Caveats

Code which contains the libstdc++ version of std::variant currently won't compile with Clang 6.0.1 because of some issue with friend template functions.

Results

BLINKY

Compiler	Optimizations	Text	Data
GCC 7.3.0	-O2	4316	20
GCC 7.3.0	-Os	4036	20
GCC 7.3.0	-O2 -flto	2520	12
GCC 7.3.0	-Os -flto	2480	12
GCC 8.2.0	-O2	4320	20
GCC 8.2.0	-Os	4044	20
GCC 8.2.0	-O2 -flto	2524	12
GCC 8.2.0	-Os -flto	2480	12
Clang 6.0.1	-O2	4208	20
Clang 6.0.1	-Os	4160	20
Clang 6.0.1	-Oz	4008	20
Clang 6.0.1	-O2 -flto	2784	12
Clang 6.0.1	-Os -flto	2504	12
Clang 6.0.1	-Oz -flto	2412	12

HELLO_WORLD

Compiler	Optimizations	Text	Data
GCC 7.3.0	-O2	6984	120
GCC 7.3.0	-Os	6696	120
GCC 7.3.0	-O2 -flto	5196	112
GCC 7.3.0	-Os -flto	5140	112
GCC 8.2.0	-O2	6996	120
GCC 8.2.0	-Os	6712	120
GCC 8.2.0	-O2 -flto	5208	112
GCC 8.2.0	-Os -flto	5148	112
Clang 6.0.1	-O2	6892	120
Clang 6.0.1	-Os	6840	120
Clang 6.0.1	-Oz	6668	120
Clang 6.0.1	-O2 -flto	5444	112
Clang 6.0.1	-Os -flto	5164	112
Clang 6.0.1	-Oz -flto	5060	112

I2C_SLAVE

Compiler	Optimizations	Text	Data
GCC 7.3.0	-O2	8080	120
GCC 7.3.0	-Os	7736	120
GCC 7.3.0	-O2 -flto	6552	112
GCC 7.3.0	-Os -flto	6360	112
GCC 8.2.0	-O2	8092	120
GCC 8.2.0	-Os	7760	120
GCC 8.2.0	-O2 -flto	6568	112
GCC 8.2.0	-Os -flto	6368	112
Clang 6.0.1	-O2	8232	120
Clang 6.0.1	-Os	8140	120
Clang 6.0.1	-Oz	7904	120
Clang 6.0.1	-O2 -flto	6880	112
Clang 6.0.1	-Os -flto	6404	112
Clang 6.0.1	-Oz -flto	6432	112

ENCODER

Compiler	Optimizations	Text	Data
GCC 7.3.0	-O2	7624	120
GCC 7.3.0	-Os	7296	120
GCC 7.3.0	-O2 -flto	5504	112
GCC 7.3.0	-Os -flto	5444	112
GCC 8.2.0	-O2	7600	120
GCC 8.2.0	-Os	7312	120
GCC 8.2.0	-O2 -flto	5520	112
GCC 8.2.0	-Os -flto	5448	112
Clang 6.0.1	-O2	7584	120
Clang 6.0.1	-Os	7516	120
Clang 6.0.1	-Oz	7264	120
Clang 6.0.1	-O2 -flto	6040	112
Clang 6.0.1	-Os -flto	5740	112
Clang 6.0.1	-Oz -flto	5596	112

TYPE_TREE_MENU

Compiler	Optimizations	Text	Data
GCC 7.3.0	-O2	10552	124
GCC 7.3.0	-Os	10332	124
GCC 7.3.0	-O2 -flto	8128	116
GCC 7.3.0	-Os -flto	8112	116
GCC 8.2.0	-O2	10676	124
GCC 8.2.0	-Os	10344	124
GCC 8.2.0	-O2 -flto	8108	116
GCC 8.2.0	-Os -flto	8068	116
Clang 6.0.1	-O2	10456	124
Clang 6.0.1	-Os	10292	124
Clang 6.0.1	-Oz	10116	124
Clang 6.0.1	-O2 -flto	8932	116
Clang 6.0.1	-Os -flto	8424	116
Clang 6.0.1	-Oz -flto	8240	116

LUA

Compiler	Optimizations	Text	Data
GCC 7.3.0	-O2	139344	584
GCC 7.3.0	-Os	127704	584
GCC 7.3.0	-O2 -flto	137824	580
GCC 7.3.0	-Os -flto	125768	580
GCC 8.2.0	-O2	140156	576
GCC 8.2.0	-Os	128460	576
GCC 8.2.0	-O2 -flto	138444	580
GCC 8.2.0	-Os -flto	126612	580
Clang 6.0.1	-O2	169728	580
Clang 6.0.1	-Os	137184	580
Clang 6.0.1	-Oz	132208	580
Clang 6.0.1	-O2 -flto	255728	576
Clang 6.0.1	-Os -flto	144600	576
Clang 6.0.1	-Oz -flto	132084	576

Building

Prerequisites

The following packages must be installed in order to build the examples:

• arm-none-eabi-gcc 7.3.0.1 8.2.0
• arm-none-eabi-newlib 3.0.0.1 3.0.0.2
• arm-none-eabi-binutils 2.31.1
• clang 6.0.1-1

In case your installation of arm-none-eabi does not default to /usr/arm-none-eabi please make sure to adjust the paths in mk/gcc-arm.mk and mk/clang-arm.mk. The toolchains can be switched by passing the additional symbol CLANG to make.

So this runs the GCC build:

make

And this runs the Clang build:

make CLANG=1

Both, GCC and Clang, make use of the libstdc++ implementation from the arm_none_eabi package.