Hi Suwa-san,
On Mon, Jan 23, 2023 at 7:43 PM Takayuki 'January June' Suwa
<[email protected]> 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
