Puzzle about macro MIPS_PROLOGUE_TEMP_REGNUM
Hi : I found the temp register used for saving registers when expanding prologue is defined by macro MIPS_PROLOGUE_TEMP_REGNUM on mips target, like: #define MIPS_PROLOGUE_TEMP_REGNUM \ (cfun->machine->interrupt_handler_p ? K0_REG_NUM : GP_REG_FIRST + 3) I don't understand why using registers starting from $3? in my application, I have to save DFmode fpu regs through gpr regs, that is $3,$4 in this case, just like : mfc1 $3, $fpr sw $3, addr mfc1 $4, $fpr+1 sw $4, addr+4 apparently this would crush the argument in $4. Here is question, why don't use $8 for MIPS_PROLOGUE_TEMP_REGNUM like EPILOGUE_TEMP? Or have I done something wrong? So, any clarification? Thanks in advance. -- Best Regards.
Re: Puzzle about macro MIPS_PROLOGUE_TEMP_REGNUM
"Amker.Cheng" writes: >I found the temp register used for saving registers when expanding > prologue is defined by > macro MIPS_PROLOGUE_TEMP_REGNUM on mips target, like: > > #define MIPS_PROLOGUE_TEMP_REGNUM \ > (cfun->machine->interrupt_handler_p ? K0_REG_NUM : GP_REG_FIRST + 3) > > I don't understand why using registers starting from $3? > in my application, I have to save DFmode fpu regs through gpr regs, > that is $3,$4 in this case, > just like : > mfc1 $3, $fpr > sw $3, addr > mfc1 $4, $fpr+1 > sw $4, addr+4 > > apparently this would crush the argument in $4. Why not use $3 in all cases? Why switch to $4? > why don't use $8 for MIPS_PROLOGUE_TEMP_REGNUM like EPILOGUE_TEMP? $8 can hold an argument value. I think $13 would be a possibility, but I don't see anything wrong with $3. Ian
Re: Puzzle about macro MIPS_PROLOGUE_TEMP_REGNUM
"Amker.Cheng" writes: > Hi : >I found the temp register used for saving registers when expanding > prologue is defined by > macro MIPS_PROLOGUE_TEMP_REGNUM on mips target, like: > > #define MIPS_PROLOGUE_TEMP_REGNUM \ > (cfun->machine->interrupt_handler_p ? K0_REG_NUM : GP_REG_FIRST + 3) > > I don't understand why using registers starting from $3? It's not "starting from $3". It's $3 and nothing else ;-) It's not intended to be used as (MIPS_PROLOGUE_TEMP_REGNUM + N). $3 was chosen because it's a MIPS16 register, and can therefore be used for both MIPS16 and normal-mode code. $2 used to be the static chain register, which left $3 as the only free call-clobbered MIPS16 register. I changed the static chain register to $15 to avoid a clash with the MIPS16 gp-load sequence: http://gcc.gnu.org/ml/gcc-patches/2008-08/msg00622.html so $2 is probably free now too. Richard
Re: Puzzle about macro MIPS_PROLOGUE_TEMP_REGNUM
> > It's not "starting from $3". It's $3 and nothing else ;-) It's not > intended to be used as (MIPS_PROLOGUE_TEMP_REGNUM + N). > > $3 was chosen because it's a MIPS16 register, and can therefore > be used for both MIPS16 and normal-mode code. $2 used to be the > static chain register, which left $3 as the only free call-clobbered Thank all of you for explanation. > MIPS16 register. I changed the static chain register to $15 to avoid > a clash with the MIPS16 gp-load sequence: > > http://gcc.gnu.org/ml/gcc-patches/2008-08/msg00622.html > > so $2 is probably free now too. Seems $2 is used for gp load in MIPS16 defined by MIPS16_PIC_TEMP_REGNUM, which should not conflict with MIPS_PROLOGUE_TEMP_REGNUM either. Mips target uses mips_split_doubleword_move in mips_save_reg to implement double float reg saving. Seems I have to provide a special pattern using exactly the only (MIPS_PROLOGUE_TEMP_REGNUM) register, rather than paired registers starting from it. But, more patterns might result in consuming more memory, time. Since my application is some kinda very unique(o32 abi and no MIPS16), maybe I could use some paired temporary register in this purpose, like $8-$15, $24-$25. Thanks. -- Best Regards.
