[PATCH] [arm] Implement Armv8.1-M low overhead loops

[Andrea Corallo]

Hi all,

This patch enables the Armv8.1-M Mainline LOB (low overhead branch) extension
low overhead loops (LOL) feature by using the loop-doloop pass
that it shares with the Swing Modulo Scheduler.

bootstrapped arm-none-linux-gnueabihf, does not introduce testsuite regressions.

Andrea

gcc/ChangeLog:

2020-??-??  Andrea Corallo  <andrea.corallo@arm.com>
2020-??-??  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>
2020-??-??  Iain Apreotesei  <iain.apreotesei@arm.com>

        * config/arm/arm.c (TARGET_INVALID_WITHIN_DOLOOP):
        (arm_invalid_within_doloop): Implement invalid_within_doloop hook.
        * config/arm/arm.h (TARGET_HAVE_LOB): Add new macro.
        * config/arm/thumb2.md (*doloop_end, doloop_begin, dls_insn):
        Add new patterns.
        * config/arm/unspecs.md: Add new unspec.

gcc/testsuite/ChangeLog:

2020-??-??  Andrea Corallo  <andrea.corallo@arm.com>
2020-??-??  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>
2020-??-??  Iain Apreotesei  <iain.apreotesei@arm.com>

        * gcc.target/arm/lob.h: New header.
        * gcc.target/arm/lob1.c: New testcase.
        * gcc.target/arm/lob2.c: Likewise.
        * gcc.target/arm/lob3.c: Likewise.
        * gcc.target/arm/lob4.c: Likewise.
        * gcc.target/arm/lob5.c: Likewise.
        * gcc.target/arm/lob6.c: Likewise.

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