[polly][ScheduleOptimizer] Fix long compile time(hang) reported in polly

[kartcq]

[polly][ScheduleOptimizer] There is no upper cap set on current Schedule Optimizer to compute schedule. In some cases a very long compile time taken to compute the schedule resulting in hang kind of behavior. This patch introduces a flag 'polly-schedule-computeout' to pass the cap which is initialized to 300000. This patch handles the compute out cases by bailing out and exiting gracefully.

This patch fixes the bug reported under polly : #69090

[efriedma-quic]

The isl_options_set_on_error thing still seems like an issue; there's a path to restore on_error, but it doesn't run if the quota is hit.

Do we actually need to explicitly check hasQuotaExceeded() at all? If there's an error, the schedule should be null, and there's already a check for if (Schedule.is_null()).

[kartcq]

Thanks for your comments @efriedma-quic

> The isl_options_set_on_error thing still seems like an issue; there's a path to restore on_error, but it doesn't run if the quota is hit.
Your concern makes sense. I have removed the early return there.

> Do we actually need to explicitly check hasQuotaExceeded() at all? If there's an error, the schedule should be null, and there's already a check for if (Schedule.is_null()).
I will still choose to keep hasQuotaExceeded() function to add a debug print indicating the reason for bailout as quota exceeded.

[kartcq]

ping @efriedma-quic @xgupta

[efriedma-quic]

LGTM

[avillega]

I think this change might be breaking some of our builds, please revert if possible.
This is the error I am getting:

******************** TEST 'Polly :: ScheduleOptimizer/schedule_computeout.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 1: /b/s/w/ir/x/w/llvm_build/tools/clang/stage2-bins/bin/opt -S -polly-optree -polly-delicm  -polly-opt-isl -polly-schedule-computeout=100000 -debug-only="polly-opt-isl" < /b/s/w/ir/x/w/llvm-llvm-project/polly/test/ScheduleOptimizer/schedule_computeout.ll 2>&1 | /b/s/w/ir/x/w/llvm_build/tools/clang/stage2-bins/bin/FileCheck /b/s/w/ir/x/w/llvm-llvm-project/polly/test/ScheduleOptimizer/schedule_computeout.ll
+ /b/s/w/ir/x/w/llvm_build/tools/clang/stage2-bins/bin/opt -S -polly-optree -polly-delicm -polly-opt-isl -polly-schedule-computeout=100000 -debug-only=polly-opt-isl
+ /b/s/w/ir/x/w/llvm_build/tools/clang/stage2-bins/bin/FileCheck /b/s/w/ir/x/w/llvm-llvm-project/polly/test/ScheduleOptimizer/schedule_computeout.ll
/b/s/w/ir/x/w/llvm-llvm-project/polly/test/ScheduleOptimizer/schedule_computeout.ll:94:10: error: CHECK: expected string not found in input
; CHECK: Schedule optimizer calculation exceeds ISL quota
         ^
<stdin>:1:1: note: scanning from here
opt: Unknown command line argument '-debug-only=polly-opt-isl'. Try: '/b/s/w/ir/x/w/llvm_build/tools/clang/stage2-bins/bin/opt --help'
^
<stdin>:2:20: note: possible intended match here
opt: Did you mean '--debug-pass=polly-opt-isl'?
                   ^

Input file: <stdin>
Check file: /b/s/w/ir/x/w/llvm-llvm-project/polly/test/ScheduleOptimizer/schedule_computeout.ll

-dump-input=help explains the following input dump.

Input was:
<<<<<<
            1: opt: Unknown command line argument '-debug-only=polly-opt-isl'. Try: '/b/s/w/ir/x/w/llvm_build/tools/clang/stage2-bins/bin/opt --help' 
check:94'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
            2: opt: Did you mean '--debug-pass=polly-opt-isl'? 
check:94'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
check:94'1                        ?                             possible intended match
>>>>>>

--

********************

[efriedma-quic]

Pushed revert.

@kartcq please fix the test so it either doesn't depend on DEBUG output, or uses REQUIRES: asserts.