Hi Andrew On Wed, Mar 25, 2009 at 12:41, Andrew Haley <a...@redhat.com> wrote: >> Since it hasn't been fixed maybe it's a bu..*ahem*..feature? > > It's a feature. Look up "earlyclobber" in the Fine Manual.
I tried that already and it does work but I actually thought the 'earlyclobber' modifier was for situations when the compiler couldn't otherwise know that a register would be, well, clobbered early. E.g., when using 'rdtsc' or other instructions that modify a specific set of registers. In my example the compiler should be able to figure out that the register is not available for output (because it is used as input in the following line), so if this behavior is not a bug, it should be. IMO. The wording in the description of digit constraints (like "0") lead me to believe that without such a constraint, the same register would not be used for both input and output... but OK, it doesn't say that explicitly. Anyway, thanks for you answer... On a side note, the assembler for your proposal is the following: 1: b8 00 00 00 00 mov $0x0,%eax 2: 8b 0c 84 mov (%esp,%eax,4),%ecx 3: 8d 14 84 lea (%esp,%eax,4),%edx 4: 89 c8 mov %ecx,%eax 5: 89 45 fc mov %eax,0xfffffffc(%ebp) 6: 89 55 f0 mov %edx,0xfffffff0(%ebp) What is the point of line 4? Why not just: 1: b8 00 00 00 00 mov $0x0,%eax 2: 8b 0c 84 mov (%esp,%eax,4),%ecx 3: 8d 14 84 lea (%esp,%eax,4),%edx 4: 89 45 fc mov %ecx,0xfffffffc(%ebp) 5: 89 55 f0 mov %edx,0xfffffff0(%ebp) So at least there is still room for optimizations. Best /Kasper
