https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81550
--- Comment #3 from Michael Meissner <meissner at gcc dot gnu.org> --- It isn't actually subversion id 250482 that causes the problem. I've built 250481 and 250483 compilers and there is no difference in code. I had 252844, and it shows the problem. The difference between the two is 250481 generates code that allows PRE_INC, PRE_DEC, and PRE_MODIFY on DFmode values for power7. Now, in theory it should not allow PRE_* on DFmode, since power7 supports DFmode in both traditional FPR registers and altivec registers. The traditional FPR loads and store support PRE_* forms of the instruction, but the VSX loads used for the Altivec registers don't support PRE_* (the original form of the instructions supported it, but it was removed the hardware shipped). The debug code (-mdebug=reg) shows that in theory the PRE_* support was turned off, but somewhere it getting turned back on and the lfdu is generated. If you compile the code with -mno-update, it generates the same code.
