Hi, > > I'm working on decompiling x86-64 binary programs, using branches to rebuild > > a control-flow graph and looking for loops. I've found a significant number > > of irreducible loops in gcc-produced code (irreducible loops are loops with > > more than one entry point), especially in -O3 optimized binaries, even when > > the source code is "well" structured. My experiments are done mainly on the > > SPEC CPU-2006 benchmarks. > > > > My question is: where do these irreducible loops come from? Which > > optimization pass leads to irreducible regions? Thanks in advance for any > > pointer. > > Questions right back at you: What compiler version are you using? Got > a specific exampe (test case)? > > In older releases of GCC4, jump threading sometimes resulted in > irreducible regions, but more recent GCCs carefully try to avoid them.
I am not sure that is actually true. Afaik, we only avoid this on gimple, while rtl jump threading does not care, Zdenek
