> Add -mfunction-return= option to convert function return to call and
> return thunks. The default is 'keep', which keeps function return
> unmodified. 'thunk' converts function return to call and return thunk.
> 'thunk-inline' converts function return to inlined call and return thunk.
> 'thunk-extern' converts function return to external call and return
> thunk provided in a separate object file. You can control this behavior
> for a specific function by using the function attribute function_return.
>
> Function return thunk is the same as memory thunk for -mindirect-branch=
> where the return address is at the top of the stack:
>
> __x86_return_thunk:
> call L2
> L1:
> pause
> jmp L1
> L2:
> lea 8(%rsp), %rsp|lea 4(%esp), %esp
> ret
>
> and function return becomes
>
> jmp __x86_return_thunk
>
> -mindirect-branch= tests are updated with -mfunction-return=keep to
> avoid false test failures when -mfunction-return=thunk is added to
> RUNTESTFLAGS for "make check".
>
> gcc/
>
> * config/i386/i386-protos.h (ix86_output_function_return): New.
> * config/i386/i386.c (ix86_set_indirect_branch_type): Also
> set function_return_type.
> (indirect_thunk_name): Add ret_p to indicate thunk for function
> return.
> (output_indirect_thunk_function): Pass false to
> indirect_thunk_name.
> (ix86_output_indirect_branch): Likewise.
> (output_indirect_thunk_function): Create alias for function
> return thunk if regno < 0.
> (ix86_output_function_return): New function.
> (ix86_handle_fndecl_attribute): Handle function_return.
> (ix86_attribute_table): Add function_return.
> * config/i386/i386.h (machine_function): Add
> function_return_type.
> * config/i386/i386.md (simple_return_internal): Use
> ix86_output_function_return.
> (simple_return_internal_long): Likewise.
> * config/i386/i386.opt (mfunction-return=): New option.
> (indirect_branch): Mention -mfunction-return=.
> * doc/extend.texi: Document function_return function attribute.
> * doc/invoke.texi: Document -mfunction-return= option.
>
> gcc/testsuite/
>
> * gcc.target/i386/indirect-thunk-1.c (dg-options): Add
> -mfunction-return=keep.
> * gcc.target/i386/indirect-thunk-2.c: Likewise.
> * gcc.target/i386/indirect-thunk-3.c: Likewise.
> * gcc.target/i386/indirect-thunk-4.c: Likewise.
> * gcc.target/i386/indirect-thunk-5.c: Likewise.
> * gcc.target/i386/indirect-thunk-6.c: Likewise.
> * gcc.target/i386/indirect-thunk-7.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-1.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-2.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-3.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-4.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-5.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-6.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-7.c: Likewise.
> * gcc.target/i386/indirect-thunk-attr-8.c: Likewise.
> * gcc.target/i386/indirect-thunk-bnd-1.c: Likewise.
> * gcc.target/i386/indirect-thunk-bnd-2.c: Likewise.
> * gcc.target/i386/indirect-thunk-bnd-3.c: Likewise.
> * gcc.target/i386/indirect-thunk-bnd-4.c: Likewise.
> * gcc.target/i386/indirect-thunk-extern-1.c: Likewise.
> * gcc.target/i386/indirect-thunk-extern-2.c: Likewise.
> * gcc.target/i386/indirect-thunk-extern-3.c: Likewise.
> * gcc.target/i386/indirect-thunk-extern-4.c: Likewise.
> * gcc.target/i386/indirect-thunk-extern-5.c: Likewise.
> * gcc.target/i386/indirect-thunk-extern-6.c: Likewise.
> * gcc.target/i386/indirect-thunk-extern-7.c: Likewise.
> * gcc.target/i386/indirect-thunk-inline-1.c: Likewise.
> * gcc.target/i386/indirect-thunk-inline-2.c: Likewise.
> * gcc.target/i386/indirect-thunk-inline-3.c: Likewise.
> * gcc.target/i386/indirect-thunk-inline-4.c: Likewise.
> * gcc.target/i386/indirect-thunk-inline-5.c: Likewise.
> * gcc.target/i386/indirect-thunk-inline-6.c: Likewise.
> * gcc.target/i386/indirect-thunk-inline-7.c: Likewise.
> * gcc.target/i386/ret-thunk-1.c: New test.
> * gcc.target/i386/ret-thunk-10.c: Likewise.
> * gcc.target/i386/ret-thunk-11.c: Likewise.
> * gcc.target/i386/ret-thunk-12.c: Likewise.
> * gcc.target/i386/ret-thunk-13.c: Likewise.
> * gcc.target/i386/ret-thunk-14.c: Likewise.
> * gcc.target/i386/ret-thunk-15.c: Likewise.
> * gcc.target/i386/ret-thunk-16.c: Likewise.
> * gcc.target/i386/ret-thunk-2.c: Likewise.
> * gcc.target/i386/ret-thunk-3.c: Likewise.
> * gcc.target/i386/ret-thunk-4.c: Likewise.
> * gcc.target/i386/ret-thunk-5.c: Likewise.
> * gcc.target/i386/ret-thunk-6.c: Likewise.
> * gcc.target/i386/ret-thunk-7.c: Likewise.
> * gcc.target/i386/ret-thunk-8.c: Likewise.
> * gcc.target/i386/ret-thunk-9.c: Likewise.
>
> @@ -10846,6 +10888,35 @@ output_indirect_thunk_function (bool need_bnd_p, int
> regno)
> ASM_OUTPUT_LABEL (asm_out_file, name);
> }
>
> + if (regno < 0)
> + {
> + /* Create alias for __x86.return_thunk/__x86.return_thunk_bnd. */
> + char alias[32];
> +
> + indirect_thunk_name (alias, regno, need_bnd_p, true);
> + ASM_OUTPUT_DEF (asm_out_file, alias, name);
> +#if TARGET_MACHO
> + if (TARGET_MACHO)
> + {
> + fputs ("\t.weak_definition\t", asm_out_file);
> + assemble_name (asm_out_file, alias);
> + fputs ("\n\t.private_extern\t", asm_out_file);
> + assemble_name (asm_out_file, alias);
> + putc ('\n', asm_out_file);
> + }
> +#else
> + if (USE_HIDDEN_LINKONCE)
> + {
> + fputs ("\t.globl\t", asm_out_file);
> + assemble_name (asm_out_file, alias);
> + putc ('\n', asm_out_file);
> + fputs ("\t.hidden\t", asm_out_file);
> + assemble_name (asm_out_file, alias);
> + putc ('\n', asm_out_file);
> + }
> +#endif
Again, I would hope that using generic function output machinery will avoid
dependency on used assembler here.
> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> index 59e5cc8e7e4..7b17773592b 100644
> --- a/gcc/config/i386/i386.opt
> +++ b/gcc/config/i386/i386.opt
> @@ -1026,9 +1026,13 @@ mindirect-branch=
> Target Report RejectNegative Joined Enum(indirect_branch)
> Var(ix86_indirect_branch) Init(indirect_branch_keep)
> Convert indirect call and jump to call and return thunks.
>
> +mfunction-return=
> +Target Report RejectNegative Joined Enum(indirect_branch)
> Var(ix86_function_return) Init(indirect_branch_keep)
> +Convert function return to call and return thunk.
I suppose you also want ix86_can_inline_p to check that caller&callee agree
about thunk usage
for calls/indirect jumps. For returns we do not care as optimized out return is
safe?
>
> +@item function_return("@var{choice}")
> +@cindex @code{function_return} function attribute, x86
> +On x86 targets, the @code{function_return} attribute causes the compiler
> +to convert function return with @var{choice}. @samp{keep} keeps function
> +return unmodified. @samp{thunk} converts function return to call and
> +return thunk. @samp{thunk-inline} converts function return to inlined
> +call and return thunk. @samp{thunk-extern} converts function return to
> +external call and return thunk provided in a separate object file.
Again please extend both documentation hunks so it is clear what is purpose
of this hack.
Honza
