ARM] Improve robustness of -mslow-flash-data

ARM] Improve robustness of -mslow-flash-data

Current code to handle -mslow-flash-data in machine description files
suffers from a number of issues which this patch fixes:

1) The insn_and_split in vfp.md to load a generic floating-point
constant via GPR first and move it to VFP register are guarded by
!reload_completed which is forbidden explicitely in the GCC internals
documentation section 17.2 point 3;

2) A number of testcase in the testsuite ICEs under -mslow-flash-data
when targeting the hardfloat ABI [1];

3) Instructions performing load from literal pool are not disabled.

These problems are addressed by 2 separate actions:

1) Making the splitters take a clobber and changing the expanders
accordingly to generate a mov with clobber in cases where a literal
pool would be used. The splitter can thus be enabled after reload since
it does not call gen_reg_rtx anymore;

2) Adding new predicates and constraints to disable literal pool loads
in existing instructions when -mslow-flash-data is in effect.

The patch also rework the splitter for DFmode slightly to generate an
intermediate DI load instead of 2 intermediate SI loads, thus relying on
the existing DI splitters instead of redoing their job. At last, the
patch adds some missing arm_fp_ok effective target to some of the
slow-flash-data testcases.

[1]
c-c++-common/Wunused-var-3.c
gcc.c-torture/compile/pr72771.c
gcc.c-torture/compile/vector-5.c
gcc.c-torture/compile/vector-6.c
gcc.c-torture/execute/20030914-1.c
gcc.c-torture/execute/20050316-1.c
gcc.c-torture/execute/pr59643.c
gcc.dg/builtin-tgmath-1.c
gcc.dg/debug/pr55730.c
gcc.dg/graphite/interchange-7.c
gcc.dg/pr56890-2.c
gcc.dg/pr68474.c
gcc.dg/pr80286.c
gcc.dg/torture/pr35227.c
gcc.dg/torture/pr65077.c
gcc.dg/torture/pr86363.c
g++.dg/torture/pr81112.C
g++.dg/torture/pr82985.C
g++.dg/warn/Wunused-var-7.C
and a lot more in libstdc++ in special_functions/*_comp_ellint_* and
special_functions/*_ellint_* directories.

2018-12-14  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    gcc/
    * config/arm/arm.md (arm_movdi): Split if -mslow-flash-data and
    source is a constant that would be loaded by literal pool.
    (movsf expander): Generate a no_literal_pool_sf_immediate insn if
    -mslow-flash-data is present, targeting hardfloat ABI and source is a
    float constant that cannot be loaded via vmov.
    (movdf expander): Likewise but generate a no_literal_pool_df_immediate
    insn.
    (arm_movsf_soft_insn): Split if -mslow-flash-data and source is a
    float constant that would be loaded by literal pool.
    (softfloat constant movsf splitter): Splitter for the above case.
    (movdf_soft_insn): Split if -mslow-flash-data and source is a float
    constant that would be loaded by literal pool.
    (softfloat constant movdf splitter): Splitter for the above case.
    * config/arm/constraints.md (Pz): Document existing constraint.
    (Ha): Define constraint.
    (Tu): Likewise.
    * config/arm/predicates.md (hard_sf_operand): New predicate.
    (hard_df_operand): Likewise.
    * config/arm/thumb2.md (thumb2_movsi_insn): Split if
    -mslow-flash-data and constant would be loaded by literal pool.
    * constant/arm/vfp.md (thumb2_movsi_vfp): Likewise and disable constant
    load in VFP register.
    (movdi_vfp): Likewise.
    (thumb2_movsf_vfp): Use hard_sf_operand as predicate for source to
    prevent match for a constant load if -mslow-flash-data and constant
    cannot be loaded via vmov.  Adapt constraint accordingly by
    using Ha instead of E for generic floating-point constant load.
    (thumb2_movdf_vfp): Likewise using hard_df_operand predicate instead.
    (no_literal_pool_df_immediate): Add a clobber to use as the
    intermediate general purpose register and also enable it after reload
    but disable it constant is a valid FP constant.  Add constraints and
    generate a DI intermediate load rather than 2 SI loads.
    (no_literal_pool_sf_immediate): Add a clobber to use as the
    intermediate general purpose register and also enable it after
    reload.

2018-11-14  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    gcc/testsuite/
    * gcc.target/arm/thumb2-slow-flash-data-2.c: Require arm_fp_ok
    effective target.
    * gcc.target/arm/thumb2-slow-flash-data-3.c: Likewise.
    * gcc.target/arm/thumb2-slow-flash-data-4.c: Likewise.
    * gcc.target/arm/thumb2-slow-flash-data-5.c: Likewise.

From-SVN: r267141