On Mon, 13 Oct 2025 at 21:00, Matt Parks <[email protected]> wrote:
>
> This patch fixes PR117468:
> ARM thumb1 compilation using -ffixed-reg with r4-r7, without -Os (which
> prohibits use of high registers), produces bad high register restoration
> code that clobbers the fixed register.
>
> gcc/ChangeLog:
> PR target/117468
> * arm.cc (thumb1_prologue_unused_call_clobbered_lo_regs): Take fixed
> regs into account.
> * arm.cc (thumb1_epilogue_unused_call_clobbered_lo_regs): Take fixed
> regs into account.
>
Thanks for the update.
I think Richard has some worries / comments?
Christophe
>
> ---
> gcc/config/arm/arm.cc | 6 ++++--
> gcc/testsuite/gcc.target/arm/pr117468.c | 13 +++++++++++++
> 2 files changed, 17 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/arm/pr117468.c
>
> diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
> index bde06f3fa86..de911981a5c 100644
> --- a/gcc/config/arm/arm.cc
> +++ b/gcc/config/arm/arm.cc
> @@ -8274,7 +8274,8 @@ thumb1_prologue_unused_call_clobbered_lo_regs (void)
> bitmap prologue_live_out = df_get_live_out (ENTRY_BLOCK_PTR_FOR_FN (cfun));
>
> for (int reg = FIRST_LO_REGNUM; reg <= LAST_LO_REGNUM; reg++)
> - if (!callee_saved_reg_p (reg) && !REGNO_REG_SET_P (prologue_live_out,
> reg))
> + if (!callee_saved_reg_p (reg) && !REGNO_REG_SET_P (prologue_live_out,
> reg)
> + && !fixed_regs[reg])
> mask |= 1 << (reg - FIRST_LO_REGNUM);
> return mask;
> }
> @@ -8287,7 +8288,8 @@ thumb1_epilogue_unused_call_clobbered_lo_regs (void)
> bitmap epilogue_live_in = df_get_live_in (EXIT_BLOCK_PTR_FOR_FN (cfun));
>
> for (int reg = FIRST_LO_REGNUM; reg <= LAST_LO_REGNUM; reg++)
> - if (!callee_saved_reg_p (reg) && !REGNO_REG_SET_P (epilogue_live_in,
> reg))
> + if (!callee_saved_reg_p (reg) && !REGNO_REG_SET_P (epilogue_live_in, reg)
> + && !fixed_regs[reg])
> mask |= 1 << (reg - FIRST_LO_REGNUM);
> return mask;
> }
> diff --git a/gcc/testsuite/gcc.target/arm/pr117468.c
> b/gcc/testsuite/gcc.target/arm/pr117468.c
> new file mode 100644
> index 00000000000..dc2dd9720ec
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/arm/pr117468.c
> @@ -0,0 +1,13 @@
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -ffixed-r7" } */
> +/* { dg-require-effective-target arm_arch_v5t_thumb_ok } */
> +/* { dg-add-options arm_arch_v5t_thumb } */
> +void ext_func(int e1, int e2, int e3, int e4);
> +
> +int bad_func(int p1, int p2, int p3, int p4) {
> + ext_func(p4, p3, p2, p1);
> + return p1 + p2 + p3 + p4;
> +}
> +
> +/* { dg-final { scan-assembler-not "pop.*r7" } } */
> --
> 2.34.1
