Hi Suwa-san, On Mon, Jan 23, 2023 at 7:43 PM Takayuki 'January June' Suwa <jjsuwa_sys3...@yahoo.co.jp> wrote: > > In the case of the CALL0 ABI, values that must be retained before and > after function calls are placed in the callee-saved registers (A12 > through A15) and referenced later. However, it is often the case that > the save and the reference are each only once and a simple register- > register move (with two exceptions; i. the register saved to/restored > from is the stack pointer, ii. the function needs an additional stack > pointer adjustment to grow the stack). > > e.g. in the following example, if there are no other occurrences of > register A14: > > ;; before > ; prologue { > ... > s32i.n a14, sp, 16 > ... ;; no frame pointer needed > ;; no additional stack growth > ; } prologue > ... > mov.n a14, a6 ;; A6 is not SP > ... > call0 foo > ... > mov.n a8, a14 ;; A8 is not SP > ... > ; epilogue { > ... > l32i.n a14, sp, 16 > ... > ; } epilogue > > It can be possible like this: > > ;; after > ; prologue { > ... > (no save needed) > ... > ; } prologue > ... > s32i.n a6, sp, 16 ;; replaced with A14's slot > ... > call0 foo > ... > l32i.n a8, sp, 16 ;; through SP > ... > ; epilogue { > ... > (no restoration needed) > ... > ; } epilogue > > This patch adds the abovementioned logic to the function prologue/epilogue > RTL expander code. > > gcc/ChangeLog: > > * config/xtensa/xtensa.cc (machine_function): Add new member > 'eliminated_callee_saved_bmp'. > (xtensa_can_eliminate_callee_saved_reg_p): New function to > determine whether the register can be eliminated or not. > (xtensa_expand_prologue): Add invoking the above function and > elimination the use of callee-saved register by using its stack > slot through the stack pointer (or the frame pointer if needed) > directly. > (xtensa_expand_prologue): Modify to not emit register restoration > insn from its stack slot if the register is already eliminated. > > gcc/testsuite/ChangeLog: > > * gcc.target/xtensa/elim_callee_saved.c: New. > --- > gcc/config/xtensa/xtensa.cc | 130 ++++++++++++++---- > .../gcc.target/xtensa/elim_callee_saved.c | 32 +++++ > 2 files changed, 137 insertions(+), 25 deletions(-) > create mode 100644 gcc/testsuite/gcc.target/xtensa/elim_callee_saved.c
This version results in multiple ICEs with the following stack traces: gcc/testsuite/gcc.c-torture/compile/20000127-1.c:7:1: error: could not split insn (insn 7 6 8 2 (set (mem/c:SI (plus:SI (reg/f:SI 15 a15) (const_int 24 [0x18])) [3 S4 A32]) (reg:DF 2 a2)) "gcc/testsuite/gcc.c-torture/compile/20000127-1.c":4:10 61 {movdf_internal} (nil)) during RTL pass: final gcc/testsuite/gcc.c-torture/compile/20000127-1.c:7:1: internal compiler error: in final_scan_insn_1, at final.cc:2808 0x6cb090 _fatal_insn(char const*, rtx_def const*, char const*, int, char const*) gcc/rtl-error.cc:108 0x639b17 final_scan_insn_1 gcc/final.cc:2808 0xb1817b final_scan_insn(rtx_insn*, _IO_FILE*, int, int, int*) gcc/final.cc:2887 0xb18266 final_1 gcc/final.cc:1979 0xb18f94 rest_of_handle_final gcc/final.cc:4240 0xb18f94 execute gcc/final.cc:4318 -------- gcc/testsuite/gcc.c-torture/compile/950729-1.c:39:1: error: could not split insn (insn 91 93 228 13 (set (reg:DI 4 a4) (mem/c:SI (plus:SI (reg/f:SI 15 a15) (const_int 72 [0x48])) [5 S4 A32])) "gcc/testsuite/gcc.c-torture/compile/950729-1.c":28:55 52 {movdi_internal} (nil)) during RTL pass: final gcc/testsuite/gcc.c-torture/compile/950729-1.c:39:1: internal compiler error: in final_scan_insn_1, at final.cc:2808 0x6cb090 _fatal_insn(char const*, rtx_def const*, char const*, int, char const*) gcc/rtl-error.cc:108 0x639b17 final_scan_insn_1 gcc/final.cc:2808 0xb1817b final_scan_insn(rtx_insn*, _IO_FILE*, int, int, int*) gcc/final.cc:2887 0xb18266 final_1 gcc/final.cc:1979 0xb18f94 rest_of_handle_final gcc/final.cc:4240 0xb18f94 execute gcc/final.cc:4318 -- Thanks. -- Max