Thanks a lot for your comments. I figured that the IRA was spilling to lo as adding a functional unit led to additional register pressure. On Wed, Sep 17, 2014 at 7:13 PM, Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Sep 17, 2014 at 04:59:38PM -0700, Cherry Vanc wrote: >> I added a functional unit to the MIPS 5kc backend for memory >> operations and noticed that a function started getting mtlo / mflo >> instructions in the prologue/epilogue. The function does not have any >> mult/div instructions. >> >> When I debug the source of these instructions, I can only tap into the >> code path when GCC is looking for the instruction suiting the RTL >> pattern (final.c). >> >> Why are these instructions being generated when I simply just added a >> functional unit to the pipeline description ? How can I debug why they >> are being generated in the first place ? > > Add -dap to your gcc command line. Also use -S, not -c. > > Cheers, > > > Segher
