[Bug middle-end/49310] [4.7 Regression] Compile time hog in var-tracking emit

[Joost.VandeVondele at pci dot uzh.ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49310

--- Comment #4 from Joost VandeVondele <Joost.VandeVondele at pci dot uzh.ch> 2011-06-08 13:23:00 UTC ---
(In reply to comment #3)
> Using -g -O2 -fbounds-check instead of -g -O1 -fbounds-check cures it,
> or e.g. -g -O1 -fbounds-check --param max-vartrack-expr-depth=5
> speeds it up.  The programming style is very weird, and combined with
> -fbounds-check which results in huge number of bbs doesn't help it,
> plus the expression chains for the debug vars really seem to be very long (and
> at the points where bounds checking failures are reported the relevant
> registers
> holding the expressions are reused for something else).

Not so sure if I agree with your statement about my programming style ;-). 

sure timings explode with increasing max-vartrack-expr-depth, maybe the table
below can help to pick a good default ?

max-vartrack-expr-depth=2: var-tracking emit     :  32.66 (33%) usr
max-vartrack-expr-depth=3: var-tracking emit     :  33.03 (34%) usr
max-vartrack-expr-depth=4: var-tracking emit     :  33.66 (34%) usr
max-vartrack-expr-depth=5: var-tracking emit     :  33.64 (34%) usr
max-vartrack-expr-depth=6: var-tracking emit     :  34.34 (35%) usr
max-vartrack-expr-depth=7: var-tracking emit     :  35.98 (35%) usr
max-vartrack-expr-depth=8: var-tracking emit     :  42.52 (37%) usr
max-vartrack-expr-depth=9: var-tracking emit     :  48.79 (39%) usr
max-vartrack-expr-depth=10: var-tracking emit     :  53.09 (42%) usr
max-vartrack-expr-depth=12: var-tracking emit     :  74.52 (46%) usr
max-vartrack-expr-depth=14: var-tracking emit     : 118.90 (63%) usr
max-vartrack-expr-depth=16: var-tracking emit     : 313.50 (81%) usr
max-vartrack-expr-depth=18: var-tracking emit     : 833.84 (91%) usr
max-vartrack-expr-depth=20: var-tracking emit     :2527.38 (97%) usr