On Wed, Nov 25, 2015 at 12:59 AM, Jan Hubicka <hubi...@ucw.cz> wrote:
> Hi,
> PR 67548 is about LTO not supporting incremental linking. I never really
> considered our current incremental linking very useful, because it triggers
> code generation at the incremental link time basically nullifying any
> benefits of whole program optimization and in fact I think it is harmful,
> because it sort of works and w/o any warning produce not very optimized code.
>
> --- gcc/lto/lto-lang.c (revision 230847)
> +++ gcc/lto/lto-lang.c (working copy)
> @@ -819,6 +819,56 @@ lto_post_options (const char **pfilename
> if (flag_wpa)
> flag_generate_lto = 1;
>
> + /* Initialize the codegen flags according to the output type. */
> + switch (flag_lto_linker_output)
> + {
> + case LTO_LINKER_OUTPUT_REL: /* .o: incremental link producing LTO IL */
> + /* Configure compiler same way as normal frontend would do with -flto:
> + this way we read the trees (declarations & types), symbol table,
> + optimization summaries and link them. Subsequently we output new LTO
> + file. */
> + flag_lto = "";
> + flag_incremental_link = 2;
> + flag_whole_program = 0;
> + flag_wpa = 0;
> + flag_generate_lto = 1;
> + /* It would be cool to produce .o file directly, but our current
> + simple objects does not contain the lto symbol markers. Go the slow
> + way through the asm file. */
> + lang_hooks.lto.begin_section = lhd_begin_section;
> + lang_hooks.lto.append_data = lhd_append_data;
> + lang_hooks.lto.end_section = lhd_end_section;
> + if (flag_ltrans)
> + error ("-flinker-output=rel and -fltrans are mutually exclussive");
> + break;
> +
> + case LTO_LINKER_OUTPUT_NOLTOREL: /* .o: incremental link producing asm
> */
> + flag_whole_program = 0;
> + flag_incremental_link = 1;
> + break;
> +
> + case LTO_LINKER_OUTPUT_DYN: /* .so: PID library */
> + /* On some targets, like i386 it makes sense to build PIC library
> wihout
> + -fpic for performance reasons. So no need to adjust flags. */
> + break;
> +
> + case LTO_LINKER_OUTPUT_PIE: /* PIE binary */
> + /* If -fPIC or -fPIE was used at compile time, be sure that
> + flag_pie is 2. */
> + if (!flag_pie && flag_pic)
> + flag_pie = flag_pic;
> + flag_pic = 0;
^^^^^^^^^^^^^^^^ This is wrong since PIE implies PIC.
This caused:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70258
> + break;
> +
>
