builds with sanitize+NDEBUG+unittests are painfully slow (esp. with gcc 7.x)

[westram]

Several modules compile incredibly slow with the above settings:

module	buildtime	buildmem
gb_aci.cxx	450s	6 Gb (1.3 Gb with 5.5)
insdel.cxx	350s
date.cxx	250s
arb_probe.cxx	170s
PT_buildtree.cxx	140s
ad_cb.cxx	140s
adquery.cxx	100s
Location.cxx	90s

(buildmem for other modules between 1-3 Gb, measured with gcc 7.2)

Functions were marked with comments by [16637]:

• all affected functions are in unittest code!
• eliminating these functions does also eliminate the problem

Build times for gcc6.3 are approx. 50-60% of 7.x times.

overall build time:

gcc	affected+UT	all-UT	affected-UT
5.5	9m40s	5m20s	1m
6.3	9m30s	5m20s	1m
7.x	16m30s	6m10s	1m

(UT=unittests, rebuilded affected or all modules)

---

Problem is caused by optimization.

I tried to disable several optimizations on file- and function-basis using one/some/all of

-fno-var-tracking
-fno-var-tracking-assignments
-fno-gcse
-fno-tree-pta 
-fno-tree-pre
-fno-tree-vectorize
-fno-unit-at-a-time 
-fno-expensive-optimizations

Several did perform slightly better, while overall speed remained more or less the same.

I've also tried to split long test functions into several smaller ones - also no real gain.

[westram]

by [16649]

Changed optimization of several test functions:

• disable var-tracking
• optimize for size instead of speed
• (some function only) disable GCSE