tree-loop-vectorization of gcc-6.x doesnt work with arb

[westram]

Effects:

• several unittests using ptserver fail (namely: MULTI_PROBE arb_test AWTC arb_probe) fixed by [15590]
• (AISC_ERRORs reported earlier were bogus-errors; caused by ptserver-crash or -malfunction?)
• calling probe design from arb fails with same error fixed by [15532]

---

Errors disappear by changing any single of the following conditions:

• use DEBUG=1
• use SANITIZE=all
• use -O2 (-O3 fails)
• use -fno-tree-loop-vectorize

Behaves wrong with gcc

• 6.1.0
• 6.2.0
• 6.3.0

Vectorization has been disabled for these versions:

• [15228] disable global
• [15532] disable PROBE only
• [15590] disable POS_TREE2::init_static() only

---

Notes:

• many vectorizations (which succeeded for gcc-versions < 6) fail now ⇒ try to fix (not fixed; only added checks with exclusions)
  • 6.1: no failures outside of PROBE
  • 6.3: fails in SL/CONSENSUS
• some new vectorizations succeed ⇒ need compiler-version-dependent vectorize-checks? by [16628]
• find code causing unittest-failures
  • attempt to disable vectorization only for single/some libs works if done in probe
  • disabled loop vectorizer only for the function causing the crash ; see [15590]
    (gcc 6.x optimization is broken for that code)

[westram]

• use -fno-tree-loop-vectorize

[14812] disables -ftree-loop-vectorize (which is triggered by -O3) for gcc 6.1.0 only, providing a workaround this problem.

It's unclear whether the wrong behavior is a in gcc or in arb:

• if unittests keep failing in subsequent gcc-versions (6.1.1, 6.2.x, ..) ⇒ most likely a in arb
• otherwise ⇒ in gcc 6.1.0

[westram]

test with gcc 6.2.0

[westram]

• fails for gcc 6.3.0 as well
• [15488] adds error for future gcc-versions including pointer to this ticket

[westram]

stop for now:

• main problem fixed in branch 'vectorize'
• checks for loop-optimization needs to get more fine-grained, because several optimizations fail with gcc 6.x and other optimizations succeed where they didn't with older gcc versions

[westram]

Replying to westram:

• checks for loop-optimization needs to get more fine-grained, because several optimizations fail with gcc 6.x and other optimizations succeed where they didn't with older gcc versions

fine grained loop-optimization-checks added with [16628]