Hi,
On Tue, Sep 05, 2017 at 11:27:25PM +0200, Jakub Jelinek wrote:
> On powerpc with sysv4 -fPIC we emit something like
> .LCL0:
> .long .LCTOC1-.LCF0
> before we start emitting the function, and in the prologue we emit
> .LCF0:
> and some code. This fails to assemble if the prologue is emitted in a
> different partition from the start of the function, as e.g. the following
> testcase, where the start of the function is hot, i.e. in .text section,
> but the shrink-wrapped prologue is cold, emitted in .text.unlikely section.
> .LCL0 is still emitted in the section the function starts, thus .text, and
> there is no relocation for subtraction of two symbols in other sections
> (the second - operand has to be in the current section so that a PC-relative
> relocation can be used). This probably never worked, but is now more
> severe, as we enable hot/cold partitioning in GCC 8, where it
> has been previously only enabled for -fprofile-use.
I wonder if that helps performance at all, for rs6000 anyway... It's is
a never-ending source of ICEs though :-(
> --- gcc/config/rs6000/rs6000.c.jj 2017-09-04 09:55:28.000000000 +0200
> +++ gcc/config/rs6000/rs6000.c 2017-09-04 16:36:49.033213325 +0200
> @@ -25248,12 +25248,15 @@ get_TOC_alias_set (void)
>
> /* This returns nonzero if the current function uses the TOC. This is
> determined by the presence of (use (unspec ... UNSPEC_TOC)), which
> - is generated by the ABI_V4 load_toc_* patterns. */
> + is generated by the ABI_V4 load_toc_* patterns.
> + Return 2 instead of 1 if the load_toc_* pattern is in the function
> + partition that doesn't start the function. */
> #if TARGET_ELF
> static int
> uses_TOC (void)
> {
> rtx_insn *insn;
> + int ret = 1;
>
> for (insn = get_insns (); insn; insn = NEXT_INSN (insn))
{
> if (INSN_P (insn))
> @@ -25270,10 +25273,14 @@ uses_TOC (void)
> sub = XEXP (sub, 0);
> if (GET_CODE (sub) == UNSPEC
> && XINT (sub, 1) == UNSPEC_TOC)
> - return 1;
> + return ret;
> }
> }
> }
> + else if (crtl->has_bb_partition
> + && NOTE_P (insn)
> + && NOTE_KIND (insn) == NOTE_INSN_SWITCH_TEXT_SECTIONS)
> + ret = 2;
}
> return 0;
> }
> #endif
> @@ -33304,14 +33311,20 @@ rs6000_elf_declare_function_name (FILE *
> return;
> }
>
> + int uses_toc;
> if (DEFAULT_ABI == ABI_V4
> && (TARGET_RELOCATABLE || flag_pic > 1)
> && !TARGET_SECURE_PLT
> && (!constant_pool_empty_p () || crtl->profile)
> - && uses_TOC ())
> + && (uses_toc = uses_TOC ()))
> {
> char buf[256];
>
> + if (uses_toc == 2)
> + {
> + in_cold_section_p = !in_cold_section_p;
> + switch_to_section (current_function_section ());
> + }
> (*targetm.asm_out.internal_label) (file, "LCL", rs6000_pic_labelno);
>
> fprintf (file, "\t.long ");
> @@ -33321,6 +33334,11 @@ rs6000_elf_declare_function_name (FILE *
> ASM_GENERATE_INTERNAL_LABEL (buf, "LCF", rs6000_pic_labelno);
> assemble_name (file, buf);
> putc ('\n', file);
> + if (uses_toc == 2)
> + {
> + in_cold_section_p = !in_cold_section_p;
> + switch_to_section (current_function_section ());
> + }
> }
Hrm, does that work if not hot/cold partitioning? Oh, that cannot happen
because uses_toc==2. Tricky.
Maybe this "switch to the other section" thing should be abstracted out?
Messing with in_cold_section_p is a bit dirty.
Otherwise looks okay; please add the {} in the first fragment.
Thanks,
Segher
