[PATCH, i386]: Some further movstrict cleanups

[Uros Bizjak <ubizjak at gmail dot com>]

Attached patch allows only SUBREGs as output operands to movstrict
expander and further allows only register operand outputs in various
corresponding splitters. This enforces the restriction, as documented
for STRICT_LOW_PART RTX:

     This expression code is used in only one context: as the
     destination operand of a 'set' expression.  In addition, the
     operand of this expression must be a non-paradoxical 'subreg'
     expression.

Additionally, the patch removes post-reload calls to movstrict
expander and consequently constructs RTXes involving STRICT_LOW_PART
with hard registers "by hand".

2019-07-30  Uroš Bizjak  <ubizjak@gmail.com>

    * config/i386/i386.md (movstrict<mode>): Use register_operand
    predicate for operand 0.  Add expander condition.  Assert that
    operand 0 is a SUBREG RTX.
    (*movstrict<mode>_1): Use register_operand predicate for operand 0.
    Update operand constraints and insn condition.
    (zero_extend<mode>si2_and): Do not call gen_movstrict<mode>.
    (zero_extendqihi2_and): Do not call gen_movstrictqi.
    (*setcc_qi_slp): Use register_operand predicate for operand 0.
    Update operand 0 constraints.
    (setcc_qi_slp splitters): Use register_operand predicate for operand 0.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Committed to mainline SVN.

Uros.

Attachment: p.diff.txt
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