singlepath: singlepath crashes when divide is used and compiled from bitcode

[Emoun]

When I compile a program that includes a divide operation to bitcode (using patmos-clang -S) and then try to further compile it to assembly with patmos-llc, using the singlepath flag, it crashes.

Take this minimal code (we will refer to this as main.c):

volatile int _1 = 1;
volatile int _2 = 2;
int main(){
	return _2 / _1;
}

We compile it to LLVM bitcode using the command patmos-clang -S main.c -O2 without issue.
We then try to compile it to assembly using the command patmos-llc main.s -mpatmos-singlepath=main -O2. This fails with the following error:

[Single-path] Cannot rewrite call in main (indirect call?)
0  libLLVMSupport.so       0x00007f2c15841762 llvm::sys::PrintStackTrace(_IO_FILE*) + 50
1  libLLVMSupport.so       0x00007f2c15840f4c
2  libc.so.6               0x00007f2c1503ef20
3  libc.so.6               0x00007f2c1503ee97 gsignal + 199
4  libc.so.6               0x00007f2c15040801 abort + 321
5  libLLVMPatmosCodeGen.so 0x00007f2c175a5875
6  libLLVMCore.so          0x00007f2c15e50d09 llvm::legacy::PassManagerImpl::run(llvm::Module&) + 761
7  patmos-llc              0x00007f2c18008294
8  patmos-llc              0x00007f2c18006ec0
9  libc.so.6               0x00007f2c15021b97 __libc_start_main + 231
10 patmos-llc              0x00007f2c18006f3a
Stack dump:
0.      Program arguments: patmos-llc main.s -mpatmos-singlepath=main -O2
1.      Running pass 'Patmos Single-Path Mark (machine code)' on module 'main.s'.

Note that we are using -O2, but all other optimization levels result in the same issue. The issue is only present with the divide operator, changing it to a multiply makes the code compile successfully.
Additionally, the issue is only present when first compiling to bitcode and then using patmos-llc on it. If we instead use the command patmos-clang main.c the code compiles successfully. So the issue is caused by patmos-llc having to read bitcode.

[schoeberl]

Divide is different form mul, as there is no divide instruction available on Patmos and a library routine needs to be linked in. Maybe this is a linking issue?

[Emoun]

I have investigated further, and divide only causes errors if its used in a function that is converted to singlepath. E.g. this code works fine with the command patmos-llc main.s -mpatmos-singlepath=init_func:

volatile int _1 = 1;
volatile int _2 = 2;

int init_func(){
	return _1 + _2;
}

int main(){
	int x = init_func();
	return x / _1;
}

This is because singlepath cannot handle external functions like printf and, apparently, the divide function provided by llvm. I don't know if there are any plans to remedy this in the future, but I am not planning to solve this. I will try to see if a better error message can be thrown instead of the current one.

[schoeberl]

Agree that you move on with other work. Let's just leave this issue open for now.

However, as a notice: this is not a single path generation issue, but a linking issue, as it works with patmos-clang.

That printf cannot be converted into single-path code is a different issue. Same issue as printf cannot be analyzed for a WCET bound.