[llvm] r291529 - [XRay] Implement `llvm-xray convert` -- trace file conversion

[Frédéric Riss via llvm-commits]

> On Feb 14, 2017, at 2:18 PM, Dimitry Andric <dimitry at andric.com> wrote:
> 
> On 14 Feb 2017, at 22:12, Dimitry Andric <dimitry at andric.com> wrote:
>> 
>> On 14 Feb 2017, at 21:40, Dean Michael Berris <dberris at google.com> wrote:
>>> 
>>> On Tue, Feb 14, 2017 at 12:33 PM Dimitry Andric <dimitry at andric.com> wrote:
> ...
>>> What happens here is that the test/tools/llvm-xray/X86/convert-with-debug-syms.txt test case has the following CHECK-NEXT lines:
>>> 
>>> ; CHECK-NEXT:   - { type: 0, func-id: 2, function: {{.*foo.*}}, cpu: 37, thread: 84697, kind: function-enter,
>>> ; CHECK-NEXT:       tsc: 3315356841454542 }
>>> 
>>> However, on my FreeBSD-based systems, the output for the 'foo' and 'bar' lines is formatted slightly differently, wrapping at the 'kind' key instead of the 'tsc' key:
>>> 
>>> - { type: 0, func-id: 2, function: 'foo(void)', cpu: 37, thread: 84697,
>>>     kind: function-enter, tsc: 3315356841454542 }
>>> 
>>> Any idea what causes this?  Maybe the yaml outputter is retrieving the terminal size differently somehow, and thus wrapping it at another margin?
>>> 
>>> If so, maybe there is some way of ensuring the output either never wraps, or always wraps at the same margin?
>>> 
>>> 
>>> Interesting. I've not found this before. We're currently just using the defaults for the yaml printer. There could be a way to not pretty-print, but I haven't explored that specifically.
>> 
>> I was just reading include/llvm/Support/YAMLTraits.h, and there it has:
>> 
>> Output(llvm::raw_ostream &, void *Ctxt = nullptr, int WrapColumn = 70);
>> 
>> and xray-converter.cc instantiates an Output object with only the raw_ostream specified, so it should indeed use the default WrapColumn.
>> 
>> However, when I just ran this on Ubuntu, it *didn't* wrap at 70 columns.  The output was this, instead:
>> 
>> ---
>> header:
>> version:         1
>> type:            0
>> constant-tsc:    true
>> nonstop-tsc:     true
>> cycle-frequency: 2601000000
>> records:
>> - { type: 0, func-id: 3, function: main, cpu: 37, thread: 84697, kind: function-enter,
>>     tsc: 3315356841453914 }
>> - { type: 0, func-id: 2, function: 'foo()', cpu: 37, thread: 84697, kind: function-enter,
>>     tsc: 3315356841454542 }
>> - { type: 0, func-id: 2, function: 'foo()', cpu: 37, thread: 84697, kind: function-exit,
>>     tsc: 3315356841454670 }
>> - { type: 0, func-id: 1, function: 'bar()', cpu: 37, thread: 84697, kind: function-enter,
>>     tsc: 3315356841454762 }
>> - { type: 0, func-id: 1, function: 'bar()', cpu: 37, thread: 84697, kind: function-exit,
>>     tsc: 3315356841454802 }
>> - { type: 0, func-id: 3, function: main, cpu: 37, thread: 84697, kind: function-exit,
>>     tsc: 3315356841494828 }
>> ...
>> 
>> It turns out this is apparently influenced by the LANG setting, which is en_US.UTF-8 on Ubuntu, and then the column counting in the YAML Output traits don't work as expected?  With LANG=C, it properly wraps at 70 chars.
> 
> I've been reading lib/Support/YAMLTraits.cpp, but I don't completely understand the wrapping logic.  The wrap column is only checked in a few specific instances, and not in every output() method.  Frederic Riss originally implemented this, so maybe he can enlighten us?

Wow I didn’t have any recollection of this… Anyway, I didn’t implement the line-wrapping, I just made it conditional.

Fred

> 
> In any case, I think it is better to make the llvm-xray output independent of wrapping columns, so setting WrapColumn to 0 explicitly.  I have submitted https://reviews.llvm.org/D29962 for this.
> 
> -Dimitry
>