[LLVMdev] llvm-stress for fuzzing llvm

[Rotem, Nadav]

Hi, 

Compiling lots of 'junk' helps in catching bugs.  I added a new tool (located under llvm/tools/llvm-stress) for generating random LL files.  The tool can be used to test different llvm components using various compilation flags.  Until now, I only found bugs in the codegen, and not in general llvm optimizations. This probably means that the generated tests are currently too simple for the higher-level optimizations. 

The command line below generates a random ll file, and llc compiles this file. It often crashes. 

./llvm-stress -seed $RANDOM -o tmp.ll -size 1000 ; ./llc tmp.ll -mcpu=corei7-avx -mattr=+avx -o /dev/null 

The "-seed" flag sets the initial seed to be used by the random function.  I implemented a simple portable 'random' function so that the result should be identical on all platforms. The initial seed also appears in the name of the generated function.  The "-size" parameter sets the size of the generated random file. 

Nadav
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