[LLVMdev] Bug in optimization pass related to strcmp and bigendian back-ends

[Nick Lewycky]

Stripf, Timo wrote:
> I thought the LLVM IR is target independent

Yes.

  and that "llvm-gcc -c -emit-llvm -O2" produces target independent code.

No.

> I'm working on a back-end and use llvm-gcc to first generate the bc file. Afterwards I use llc including the new back-end to produce the assembler file.

LLVM IR contains a target-information line but is otherwise target 
independent. This does *not* mean that you can convert C to LLVM IR in a 
target independent way.

C code may contain "#ifdef __ppc__". Now what? Or how about "switch (x) 
{ case sizeof(int): ... }". This question is a FAQ: 
http://llvm.org/docs/FAQ.html#platformindependent

LLVM IR is portable in the sense that it will run the same on any 
platform. C is portable in the sense that you can detect things about 
the platform so you may correct for them. It turns out that these are 
two fundamentally incompatible paradigms.

Some LLVM optimizations take advantage of the information in the target 
info line which could change the behaviour of the program if your target 
system doesn't match the one described in the info line.

Nick