LLVM xray profiling

[raphdev]

This PR adds required flags to compile debug builds with LLVM Xray to allow profiling, controlled similarly to sanitizers in #35. With xray instrumentation, we can capture traces and use the llvm-xray tool to convert the output to different formats. See Agoric/agoric-sdk#7068 for context.

To use (from agoric-sdk):

cd packages/xsnap
SANITIZER=xray yarn build
# enable instrumentation via env var
XRAY_OPTIONS="xray_mode=xray-basic prepatch_main=true verbosity=1" yarn test

Each run of xsnap will print its PID and output:

==51498==XRay: Log file in 'xray-log.xsnap-worker.zUy3ve'

We can parse xray-log.xsnap-worker.zUy3ve with llvm-xray:

llvm-xray account xray-log.xsnap-worker.zUy3ve --instr_map ./xsnap-native/xsnap/build/bin/lin/debug/xsnap-worker --top=3 --sort=sum --sortorder=dsc
Functions with latencies: 218
   funcid      count [      min,       med,       90p,       99p,       max]       sum  function    
     1434          2 [ 3.126452,  3.129465,  3.129465,  3.129465,  3.129465]  6.255916  xsRun.c:0:0: fxRunID
       97          1 [ 3.129466,  3.129466,  3.129466,  3.129466,  3.129466]  3.129466  xsAPI.c:0:0: fxRunCount
      946          1 [ 3.129462,  3.129462,  3.129462,  3.129462,  3.129462]  3.129462  xsGlobal.c:0:0: fx_eval

llvm-xray stack xray-log.xsnap-worker.zUy3ve --instr_map ./xsnap-native/xsnap/build/bin/lin/debug/xsnap-worker --aggregate-threads 

Unique Stacks: 280
Top 10 Stacks by leaf sum:

Sum: 1696600127
lvl   function                                                            count              sum
#0    main                                                                    0                0
#1    fxRunCount                                                              1       3129466209
#2    fxRunID                                                                 1       3129464668
#3    fx_eval                                                                 1       3129461960
#4    fxRunScript                                                             1       3126494793
#5    fxRunID                                                                 1       3126451793
#6    fxOrdinarySetProperty                                               58649       1696600127

Sum: 1553126385
lvl   function                                                            count              sum
#0    main                                                                    0                0
#1    fxRunCount                                                              1       3129466209
#2    fxRunID                                                                 1       3129464668
#3    fx_eval                                                                 1       3129461960
#4    fxRunScript                                                             1       3126494793
#5    fxRunID                                                                 1       3126451793
#6    fxRunIn                                                             62350       2306815599
#7    fxHasAt                                                             58246       2011622143
#8    fxHasAll                                                            56539       1735811985
#9    fxOrdinaryHasProperty                                               55809       1639403023
#10   fxOrdinaryGetProperty                                               55809       1553126385

We can also output formats compatible with various tools, like Chrome Event Viewer/Perfetto (chrome://tracing) to visualize as flame graphs:

llvm-xray convert xray-log.xsnap-worker.zUy3ve --instr_map ./xsnap-native/xsnap/build/bin/lin/debug/xsnap-worker --symbolize --output-format=trace_event | gzip > xsnap-test-trace.json.gz

[raphdev]

Reverted back to draft. I'm working on an alternative.