I have a question about GCC's handling of the condition codes (specifically the CF, ZF, NF, OF, PF bits in bits in EFLAGS) on the i386 that will hopefully be trivial to anyone familiar with the implementation of the i386 target. My impression is that GCC generally treats the i386 condition codes as a single pseudo-register, which some instructions change (e.g., ADD) and others don't (e.g., MOV). But some i386 instructions change only some condition code bits while leaving other bits unchanged (e.g., INC/DEC, which leave CF unchanged).
My question: does GCC-generated code ever actually depend on this aspect of the x86 architecture - i.e., on instructions that architecturally change some but not all condition codes _not_ changing those bits that they're not supposed to change? In other words, if the i386 architecture were suddenly to be modified so that all instructions that traditionally affect only some of the condition code bits suddenly instead affect _all_ condition code flags, would GCC-generated code care at all? Would the i386 backend have to be changed? My impression is the answer is no, but I'm not deeply familiar with the i386 backend enough to be sure. Thanks very much! Bryan
