LLVM + Boehm GC
2016-11-23
TechThough LLVM itself does not have a GC algorithm, it is not so difficult to use existing GC library, especially conservatice GCs like Boehm GC.
- Link Boehm GC
- Call GC_malloc instead of malloc
Prerequisites
- LLVM (eg.
brew install llvm) - Boehm GC (eg.
brew install boehmgc)
Example
declare void @GC_init()
declare i8* @GC_malloc(i64) ; Use i32 if you are using 32bit OS
; A function that allocates some memory
define i8* @foo(){
%reg1 = call i8* @GC_malloc(i64 8)
ret i8* %reg1
}
define i32 @main(){
; 0. Init BoehmGC
call void @GC_init()
; 1. Allocate some memory
%reg1 = call i8* @foo()
; 2. Write some data(123)
store i8 123, i8* %reg1
; 3. Read it
%reg2 = load i8, i8* %reg1
; 4. Return it
%reg3 = zext i8 %reg2 to i32
ret i32 %reg3
}
Save this as bgc.ll and you can run it like this.
$ llc bgc.ll
$ cc -I/usr/local/Cellar/bdw-gc/7.6.0/include/ \
-L/usr/local/Cellar/bdw-gc/7.6.0/lib/ -lgc \
-o bgc bgc.s
$ ./bgc
$ echo $?
123
