how to use llvm intrinsics @llvm.read_register?

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I noticed that llvm.read_register() could read the value of stack pointer, as well as llvm.write_register() could set the value of stack pointer. I add main function to the stackpointer.ll which could be found in the llvm src:

;stackpointer.ll  
 define i32 @get_stack() nounwind {  
 　%sp = call i32 @llvm.read_register.i32(metadata !0)  
 　ret i32 %sp  
}

declare i32 @llvm.read_register.i32(metadata) nounwind  
!0 = metadata !{metadata !"sp\00"}

define i32 @main() {  
　%1 = call i32 @get_stack()  
　ret i32 %1  
}

I tested on an armv7 board running ubuntu 11.04:

lli stackpointer.ll

then, I get a stack dump:

ARMCodeEmitter::emitPseudoInstruction  
UNREACHABLE executed at ARMCodeEmitter.cpp:847! 
Stack dump:  
0.　　Program arguments: lli stackpointer.ll  
1.　　Running pass 'ARM Machine Code Emitter' on function '@main'  
Aborted

I also tried llc:

llc stackpointer.ll -o stackpointer.s

The error messege:

Can't get register for value!  
UNREACHABLE executed at ARMCodeEmitter.cpp:1183!   
Stack dump:  
0.　　Program arguments: llc stackpointer.ll -o stackpointer.s  
1.　　Running pass 'Function Pass Manager' on moulude 'stackpointer.ll'  
2.　　Running pass 'ARM Instruction Selection' on function '@get_stack'  
Aborted  

I also tried on x86-64 platform, it didn't work. What is the correct way to use these intrinsics?

asked 1 min ago

winter333

15

how to use llvm intrinsics @llvm.read_register?