On Mon, Aug 27, 2007 at 06:11:04AM +0100, Darryl L. Miles wrote: > > [1] This issue is in the way %edx is zero'ed, I would think zeroing out > registers/memory/whatever would be a special optimization case in this > code its clear that there is no useful value in the CPU condition flags, > so "xorl %edx,%edx" would make most sense, instead of having to find > another register to load with zero before then copying. Interestingly > enough -O generates a "mov $0,%r8d", while -O2 generates a "xor %r8d,%r8d". Peephole optimization isn't performed at -O. It is usually better to post asm output from "gcc -S -dp" than "objdump --disassemble" output because the former shows which instruction pattern GCC is using. -- Rask Ingemann Lambertsen
