[PATCH][ARM] Restrict MAX_CONDITIONAL_EXECUTE when -mrestrict-it is in place

[Kyrill Tkachov]

Hi all,

When using the short Thumb2 IT blocks we want to also restrict ifcvt so that it will not end up generating a number of back-to-back cond_execs
that will later end up being back to back single-instruction IT blocks. Branching over them should be a better choice.

This patch implements that by setting max_insns_skipped to 1 when arm_restrict_it.

With this patch, I've seen GCC replace a number of sequences in places like SPEC2006 from:
     it    eq
     moveq    r1, r5
     it    ne
     movne    r1, r10
     it    eq
     moveq    r8, r4

to a branch over them.

Bootstrapped and tested on arm.
Ok for trunk?

Thanks,
Kyrill

2015-05-18  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * config/arm/arm.c (arm_option_params_internal): When optimising
     for speed set max_insns_skipped when arm_restrict_it.

2015-05-18  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

     * gcc.target/arm/short-it-ifcvt-1.c: New test.
     * gcc.target/arm/short-it-ifcvt-2.c: Likewise.
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