On 11/07/2025 02:21, Alexandre Oliva wrote:
>
> When a function call uses up all argument registers, and needs IP for
> the static chain, there isn't any call-clobbered register left for
> reload to assign as the sibcall target, when -mlong-calls is enabled.
> Use the same logic that does the job for indirect calls to prevent
> tail calls in this case.
>
> With this change, it is possible to bootstrap armv7a-linux-gnu with
> both -O3 and lto, but only with both -mlong-calls and
> -ffunction-sections.
>
> Without -mlong-calls, linker veneer thunks may clobber the static
> chain register set up by callers in one lto unit, preventing them from
> reaching the callee in a separate lto unit. -ffunction-sections is
> required for -mlong-calls to be effective, because both caller and
> callee are in the same section, and that disables long-calls when
> !flag_reorder_blocks_and_partition.
>
> Regstrapped on armv7a-linux-gnu with the caveats above. Ok to install?
>
>
> for gcc/ChangeLog
>
> PR target/119430
> * gcc/config/arm.cc (arm_function_ok_for_sibcall): Disable
> sibcalls for long-calls that use all call-clobbered
> general-purpose registers, including the static chain.
I just noticed that this never got reviewed. Sorry about that.
I tweaked the comment above this section and fixed the commit message before
pushing it
Thanks for the patch.
R.
> ---
> gcc/config/arm/arm.cc | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/config/arm/arm.cc b/gcc/config/arm/arm.cc
> index bde06f3fa8664..8956b8a645f2c 100644
> --- a/gcc/config/arm/arm.cc
> +++ b/gcc/config/arm/arm.cc
> @@ -7946,9 +7946,12 @@ arm_function_ok_for_sibcall (tree decl, tree exp)
> function arguments, then we can only use IP. But IP may be needed in
> the
> epilogue (for PAC validation), or for passing the static chain. We have
> to disable the tail call if nothing is available. */
> - if (!decl
> - && ((CALL_EXPR_BY_DESCRIPTOR (exp) && !flag_trampolines)
> - || arm_current_function_pac_enabled_p()))
> + if ((!decl
> + && ((CALL_EXPR_BY_DESCRIPTOR (exp) && !flag_trampolines)
> + || arm_current_function_pac_enabled_p ()))
> + || (decl && arm_is_long_call_p (decl)
> + && (CALL_EXPR_STATIC_CHAIN (exp)
> + || arm_current_function_pac_enabled_p ())))
> {
> tree fntype = TREE_TYPE (TREE_TYPE (CALL_EXPR_FN (exp)));
> CUMULATIVE_ARGS cum;
>
>
