r266605 - in /trunk/gcc: ChangeLog config.in co...

[amodra@gcc.gnu.org]

Author: amodra
Date: Thu Nov 29 04:53:49 2018
New Revision: 266605

URL: https://gcc.gnu.org/viewcvs?rev=266605&root=gcc&view=rev
Log:
[RS6000] inline plt call sequences

Finally, the point of the previous patches in this series, support for
inline PLT calls, keyed off -fno-plt.  This emits code using new
relocations that tie all insns in the sequence together, so that the
linker can edit the sequence back to a direct call should the call
target turn out to be local.  An example of ELFv2 code to call puts is
as follows:

     .reloc .,R_PPC64_PLTSEQ,puts
        std 2,24(1)
     .reloc .,R_PPC64_PLT16_HA,puts
        addis 12,2,0
     .reloc .,R_PPC64_PLT16_LO_DS,puts
        ld 12,0(12)
     .reloc .,R_PPC64_PLTSEQ,puts
        mtctr 12
     .reloc .,R_PPC64_PLTCALL,puts
        bctrl
        ld 2,24(1)

"addis 12,2,puts@plt@ha" and "ld 12,puts@plt@l(12)" are also supported
by the assembler.  gcc instead uses the explicit R_PPC64_PLT16_HA and
R_PPC64_PLT16_LO_DS relocs because when the call is to __tls_get_addr
an extra reloc is emitted at every place where one is shown above, to
specify the __tls_get_addr arg.  The linker expects the extra reloc to
come first.  .reloc enforces that ordering.

The patch also changes code emitted for longcalls if the assembler
supports the new marker relocs, so that these too can be edited.  One
side effect of longcalls using PLT16 relocs is that they can now be
resolved lazily by ld.so.

I don't support lazy inline PLT calls for ELFv1, because ELFv1 would
need barriers to reliably load both the function address and toc
pointer from the PLT.  ELFv1 -fno-plt uses the longcall sequence
instead, which isn't edited by GNU ld.

	* config.in (HAVE_AS_PLTSEQ): Add.
	* config/rs6000/predicates.md (indirect_call_operand): New.
	* config/rs6000/rs6000-protos.h (rs6000_pltseq_template),
	(rs6000_sibcall_sysv): Declare.
	* config/rs6000/rs6000.c (init_cumulative_args): Set cookie
	CALL_LONG for -fno-plt.
	(print_operand <T, z, 0>): Handle UNSPEC_PLTSEQ.
	(rs6000_indirect_call_template_1): Emit .reloc directives for
	UNSPEC_PLTSEQ calls.
	(rs6000_pltseq_template): New function.
	(rs6000_longcall_ref): Add arg parameter.  Use PLT16 insns if
	relocs supported by assembler.  Move SYMBOL_REF test to callers.
	(rs6000_call_aix): Adjust rs6000_longcall_ref call.  Package
	insns in UNSPEC_PLTSEQ, preserving original func_desc.
	(rs6000_call_sysv): Likewise.
	(rs6000_sibcall_sysv): New function.
	* config/rs6000/rs6000.h (HAVE_AS_PLTSEQ): Provide default.
	* config/rs6000/rs6000.md (UNSPEC_PLTSEQ, UNSPEC_PLT16_HA,
	UNSPEC_PLT16_LO): New.
	(pltseq_tocsave, pltseq_plt16_ha, pltseq_plt16_lo, pltseq_mtctr): New.
	(call_indirect_nonlocal_sysv): Don't differentiate zero from non-zero
	cookie in constraints.  Test explicitly for flags in length attr.
	Handle unspec operand 1.
	(call_value_indirect_nonlocal_sysv): Likewise.
	(call_indirect_aix, call_value_indirect_aix): Handle unspec operand 1.
	(call_indirect_elfv2, call_value_indirect_elfv2): Likewise.
	(sibcall, sibcall_value): Use rs6000_sibcall_sysv.
	(sibcall_indirect_nonlocal_sysv): New pattern.
	(sibcall_value_indirect_nonlocal_sysv): Likewise.
	(sibcall_nonlocal_sysv, sibcall_value_nonlocal_sysv): Remove indirect
	call alternatives.
	* configure.ac: Check for gas plt sequence marker support.
	* configure: Regenerate.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config.in
    trunk/gcc/config/rs6000/predicates.md
    trunk/gcc/config/rs6000/rs6000-protos.h
    trunk/gcc/config/rs6000/rs6000.c
    trunk/gcc/config/rs6000/rs6000.h
    trunk/gcc/config/rs6000/rs6000.md
    trunk/gcc/configure
    trunk/gcc/configure.ac