On Mon, Jan 29, 2024 at 08:00:26AM -0800, H.J. Lu wrote:
> Attach REG_CFA_UNDEFINED notes for unsaved callee-saved registers which
> have been used in the function to an instruction in prologue.
>
> gcc/
>
> PR target/38534
> * dwarf2cfi.cc (add_cfi_undefined): New.
> (dwarf2out_frame_debug_cfa_undefined): Likewise.
> (dwarf2out_frame_debug): Handle REG_CFA_UNDEFINED.
> * reg-notes.def (REG_CFA_UNDEFINED): New.
> * config/i386/i386.cc (ix86_expand_prologue): Attach
> REG_CFA_UNDEFINED notes for unsaved callee-saved registers
> which have been used in the function to an instruction in
> prologue.
>
> gcc/testsuite/
>
> PR target/38534
> * gcc.target/i386/no-callee-saved-19.c: New test.
> * gcc.target/i386/no-callee-saved-20.c: Likewise.
> * gcc.target/i386/pr38534-7.c: Likewise.
> * gcc.target/i386/pr38534-8.c: Likewise.
> ---
> gcc/config/i386/i386.cc | 20 +++++++
> gcc/dwarf2cfi.cc | 55 +++++++++++++++++++
> gcc/reg-notes.def | 4 ++
> .../gcc.target/i386/no-callee-saved-19.c | 17 ++++++
> .../gcc.target/i386/no-callee-saved-20.c | 12 ++++
> gcc/testsuite/gcc.target/i386/pr38534-7.c | 18 ++++++
> gcc/testsuite/gcc.target/i386/pr38534-8.c | 13 +++++
> 7 files changed, 139 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-19.c
> create mode 100644 gcc/testsuite/gcc.target/i386/no-callee-saved-20.c
> create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-7.c
> create mode 100644 gcc/testsuite/gcc.target/i386/pr38534-8.c
>
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index b3e7c74846e..6ec87b6a16f 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -9304,6 +9304,26 @@ ix86_expand_prologue (void)
> combined with prologue modifications. */
> if (TARGET_SEH)
> emit_insn (gen_prologue_use (stack_pointer_rtx));
> +
> + if (cfun->machine->call_saved_registers
> + != TYPE_NO_CALLEE_SAVED_REGISTERS)
> + return;
> +
> + insn = get_insns ();
> + if (!insn)
> + return;
You can't attach the notes to a random instruction that happens to be first
in the function.
1) it needs to be a real instruction, not a note
2) it needs to be RTX_FRAME_RELATED_P
3) if it is RTX_FRAME_RELATED_P, but doesn't contain any previous REG_CFA_*
notes:
3a) if it has REG_FRAME_RELATED_EXPR note, then I believe just that
note argument is processed instead of the instruction pattern and
I think REG_CFA_* notes which precede REG_FRAME_RELATED_EXPR are
processed, but REG_CFA_* notes after it are not; so adding
REG_CFA_UNDEFINED notes at least if the adding is after the existing
notes instead of before them may be problematic
3b) if it has neither REG_CFA_* nor REG_FRAME_RELATED_EXPR notes, then
normally the pattern of the insn would be processed in dwarf2cfi.
But with the REG_CFA_* notes that part will be ignored.
> --- a/gcc/dwarf2cfi.cc
> +++ b/gcc/dwarf2cfi.cc
> @@ -517,6 +517,17 @@ add_cfi_restore (unsigned reg)
> add_cfi (cfi);
> }
>
Function comment missing.
> +static void
> +add_cfi_undefined (unsigned reg)
> +{
> + dw_cfi_ref cfi = new_cfi ();
> +
> + cfi->dw_cfi_opc = DW_CFA_undefined;
> + cfi->dw_cfi_oprnd1.dw_cfi_reg_num = reg;
> +
> + add_cfi (cfi);
> +}
> +
> /* Perform ROW->REG_SAVE[COLUMN] = CFI. CFI may be null, indicating
> that the register column is no longer saved. */
Jakub
